Endoscope-assisted trigeminal schwannoma resection without extensive skull-base drilling 

Endoscope-assisted trigeminal schwannoma resection without extensive skull-base drilling | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Endoscope-assisted trigeminal schwannoma resection without extensive skull-base drilling Berk Burak Berker, Abuzer Güngör, Yücel Doğruel, Serdar Rahmanov, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5211321/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract OBJECTIVE The objective of this study was to demonstrate that trigeminal schwannomas located in different cranial fossae can be resected entirely through Meckel’s cave without extensive skull-base drilling by taking either an endoscope-assisted pterional epidural approach (EA-PEA) or an endoscope-assisted lateral suboccipital retrosigmoid approach (EA-LSRA). Additionally, we describe a modified classification based on Jefferson’s system to determine the surgical approach. METHODS This is a retrospective study of 19 patients with trigeminal schwannomas in different cranial fossae who underwent EA-PEA or EA-LSRA .According to the proposed system, lesions in the middle fossa are classified as type A, those in the posterior fossa are type B, and lesions in both fossae are type C, the same as in Jefferson’s classification. Our modifications begin by classifying lesions extending into different fossae. Those located primarily in the middle cranial fossa are denoted type C1, whereas one predominantly occupying the posterior cranial fossa is type C2. Lesions with extracranial extensions are classified as type D. Patients with type A, type C1, and type D lesions underwent EA-PEA, while those with type B and C2 lesions were treated through EA-LSRA. RESULTS Thirteen patients (68.4%) underwent EA-PEA and 6 (31.6%) underwent EA-LSRA. Gross total resection was accomplished in 16 patients (84.2%). No surgery-related complications were observed. CONCLUSION Our study demonstrates that EA-PEA and EA-LSRA can lead to gross total resection in patients with complex trigeminal schwannomas. Endoscope assistance helps avoid the extensive skull-base approaches. The proposed classification system is a guide for determining the surgical approach. endoscope assistance skull base trigeminal schwannoma Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 INTRODUCTION Trigeminal schwannoma (TSch) is a rare lesion and usually considered to be benign. These tumors comprise 0.07–0.36% of intracranial tumors and 0.8–8% of intracranial schwannomas.[1–5] Surgical resection is the optimal treatment and these tumors can be cured with total resection.[6–8] As a TSch can originate from the trigeminal root, ganglion, or peripheral division of the nerve, these tumors have the potential to expand into different compartments: the posterior fossa (cerebellopontine angle), intradural space (Meckel’s cave), or extracranial spaces such as the orbita, pterygopalatine fossa, or infratemporal fossa.[9–12]However, surgery for these lesions is challenging because of their complicated incursion into different fossae and their close relations with vital structures.[13–15] Several surgical strategies for the complete removal of these tumors have been described.[8, 9, 14, 16, 17] Since the first case describing resection of a lesion in Meckel’s cave, total resection rates have increased while complication rates have decreased with the development of microsurgical skull-base techniques.[8, 18, 19] In addition to the use of microsurgical techniques, successful resection rates have been reported for a TSch located in intra- and extradural spaces because of improvements in endoscopic techniques. However, purely endoscopic approaches are not as successful as microscopic techniques for lesions located in or spreading to the posterior fossa.[20, 21]To resect a TSch that extends into multiple fossae with skull-base approaches, extensive bone removal or dissection of vascular structures is necessary to obtain adequate exposure.[8, 9, 22] However, serious complications can result from these complex approaches.[23, 24] In this study, we show that successful resection of a TSch is possible with the endoscope-assisted pterional epidural approach (EA-PEA) and the endoscope-assisted lateral suboccipital retrosigmoid approach (EA-LSRA). With endoscope assistance, we can harness the advantages of both microsurgical and endoscopic techniques, addressing the problems related to intraoperative visualization in the microsurgical procedures and effectively removing any tumor remnants noticed during endoscopy. Moreover, this technique allows total resection without additional bone removal or a petrosectomy through the natural pathway created by Meckel’s cave between the middle and posterior fossae. Additionally, we describe a modified classification for these lesions based on Jefferson’s classification system for trigeminal schwannomas. MATERIAL AND METHODS Patient Data and Outcome Assessment A series of 19 patients with TSch in different cerebral fossae were operated on via the EA-PEA or EA-LSRA in our institution by the senior author (UT) from April 2007 through May 2023. These cases were retrospectively evaluated. Among these patients, 13 underwent EA-PEA and 6 underwent EA-LSRA. Of these 6 patients, 3 underwent EA-LSRA in the lateral position and the remaining 3 in the semi-lateral position. Eighteen patients underwent surgery for the first time. However, one of these patients had gamma knife radiosurgery at another clinic but experienced progressive trigeminal neuralgia and was admitted to our clinic for microsurgical resection. The nineteenth had partial removal of the lesion at another institution. This patient was admitted to our clinic because of regrowth and associated symptoms. Neuroradiological evaluation included preoperative CT scanning, and preoperative, early postoperative (< 24 hours), and 3-month postoperative evaluations were done with magnetic resonance imaging (MRI) according to standard imaging protocols. Intraoperative MRI was introduced into our institution in January 2018. After this timepoint, this modality was used routinely. All patients underwent detailed neurological examinations at admission, after surgery, at discharge, and at follow-up. Electromyographic recordings from the seventh and eighth cranial nerves, motor evoked potentials, and somatosensory evoked potentials were obtained for patients with lesions compressing the brain stem. Table 1 shows our modified classification system, which is based on Jefferson’s trigeminal schwannoma classification. In both systems, lesions in the middle fossa are classified as type A. Lesions located in the posterior fossa are type B, and those extending into both fossae are type C. In our modification, lesions predominantly occupying the middle fossa are type C1. Conversely, tumors primarily occupying the posterior fossa are defined as type C2. Those with extracranial components are classified as type D regardless of which fossa they predominantly occupy. The surgical approach for each patient was chosen according to this modified classification. Table 1 Comparison of Jefferson’s classification and our modified classification Jefferson Classification Authors’ Modified Classification Approach Group A: Lesion occupies the middle fossa Type A: Lesion occupies the middle fossa Group B: Lesion occupies the posterior fossa Type B: Lesion occupies the posterior fossa Group C: Lesion occupies both cerebral fossae Type C1: Lesion occupies both fossae but lies predominantly in the middle fossa Type C2: Lesion occupies both fossae but lies predominantly in the posterior fossa Type D: Lesion has various extracranial expansions The volume of each tumor in each fossa was measured in cubic centimeters (cm 3 ) with the Osirix software (Pixmeo, Geneva, Switzerland), and the surgical approach was chosen according to the lesion volume in different fossae. Patients with type A and C1 lesions underwent an EA-PEA, while those with type B and C2 lesions were treated with an EA-LSRA. For patients with type D lesions, the surgical approach was determined based on the tumor volume in the respective fossae. If the tumor volume was higher in the extracranial and middle fossae together, an EA-PEA approach was done. Conversely, if the volume was higher in the posterior fossa, the EA-LSRA was chosen. Resection rates were evaluated as Samii and colleagues carried out in their study.[25] Total removal of the tumor was considered gross total resection. If less than 5% of the tumor remained after surgery, it was considered near total resection. Tumor of greater than 5% remaining was designated subtotal resection. Written informed consent was obtained from all patients, and the study was approved by our institutional review committee. Surgical Techniques Endoscope-Assisted Pterional Epidural Approach For the endoscope-assisted pterional epidural approach (EA-PEA), lumbar drainage is done preoperatively to release cerebrospinal fluid (CSF), which allows the temporal pole to be retracted with minimal risk of damage to brain tissue and to achieve adequate exposure of the tumor. A pterional craniotomy is done and the sphenoid ridge drilled and flattened. The dura is dissected away from both the frontal and temporal sides of the sphenoid ridge. The meningo-orbital band connecting the outer border of the superior orbital fossa and the frontotemporal dura is dissected and incised. The cavernous sinus is exposed extradurally, and the outer layer of the lateral wall of the cavernous sinus is separated from the inner layer, as performed by Dolenc.[8] The outer dural layer is mobilized, providing good exposure without retracting the brain, which is well protected by the preserved outer layer of the dura. Subsequently, the outer dural layer is fixed with tacking sutures without the need for a rigid retractor. Once the tumor is visualized in the intradural space, an arachnoid layer is seen surrounding the tumor.[26, 27] Preserving this layer allows tumor removal without opening the cavernous sinus and minimizes the risk of injury to the third, fourth, and sixth cranial nerves located in the lateral wall of the cavernous sinus. After the tumor is accessed and debulked in piecemeal fashion, a micro-Doppler ultrasound (Mizuho America, Inc.) is used to locate the cavernous segment of the internal carotid artery to preserve it. The posterior fossa component of a type C1 and D TSch can be totally removed through Meckel’s cave without extensive bone drilling including an anterior clinoidectomy or petrosectomy. Moreover, it can be accomplished without enlarging the foramen ovale and rotundum, reducing the risk of CSF leakage postoperatively. The tumor is removed without bipolar coagulation to preserve the integrity of adjacent structures. After excision, which is visualized through the microscope, straight (0-degree angle) and angled (30 and 45 degrees, if needed) endoscopes are used to visualize parts of Meckel’s cave and the posterior fossa that may not be visible through the microscope. If any tumor remnants are observed in Meckel’s cave or the posterior fossa at this time, they are excised either with a microscope or under endoscopic visualization without dissecting the tentorium. This approach preserves the third, fourth, and sixth cranial nerves, the superior petrosal sinus, and the petrosal vein, while ensuring complete removal of the tumor (Fig. 1 ). After the tumor bed is irrigated, Meckel’s cave is filled with an absorbable hemostatic gelatin sponge coated with polypeptides (Spongostan; Ethicon, Inc., Somerville, New Jersey) to prevent small venous bleeding from the cavernous sinus. The gelatin sponge also prevents meningocerebral adhesions and does not generate postoperative artifacts on MRI, unlike fat tissue.[28] Before closing, a small incision is made in the dura and normal saline is re-injected into the subdural space to return the dura to its normal state. The incision is then closed and the lumbar drain removed. ESM.1 Radical removal of a right-sided type C1 trigeminal schwannoma (case 13). An EA- PEA was carried out. The operation was uneventful and total resection was achieved. Endoscope-Assisted Lateral Suboccipital Retrosigmoid Approach A lateral suboccipital craniotomy with the retrosigmoid approach was done for six patients, with three in a lateral position and three in a semi-lateral position. After January 2018, the semi-lateral position has been used to accommodate intraoperative MRI. A linear lateral occipital incision is made, followed by a lateral suboccipital craniotomy. Two openings are then created in the dura. The first is placed over the lower aspect of the craniotomy to release CSF from the cisterna magna, relaxing the posterior fossa. The second incision is made 15 mm below the transverse sinus after the exact location of the transverse and sigmoid sinuses are confirmed. Then, the two openings are connected with a curvilinear incision parallel to the sigmoid sinus. When the patient is in the lateral or semi-lateral position, adequate exposure is obtained without rigid retractors through gravitational retraction of the cerebellum. Afterwards, the petrous vein, and the seventh and eighth nerves are identified. Subsequently, the arachnoid layer surrounding the tumor is identified.[26, 27] Preserving this layer allows tumor resection without injury to the roots of the fifth cranial nerve and surrounding structures. After the tumor is debulked, the fourth and fifth nerves are identified. The trigeminal nerve appears as separated fibers and is flattened due to mass effect of the lesion. For types C2 and D, the portion of tumor in the middle fossa is removed through Meckel’s cave. As some parts of the tumor in Meckel’s cave and the middle fossa are not visualized with the microscope, a 30-degree angled endoscope (or 45 degrees, if needed) is used, and any tumor remnants are removed under the microscope or endoscope visualization, if required, without tentorial dissection or additional bone drilling. This approach preserves hearing and, by preserving the arachnoid layer over the tumor, minimizes the risk of injury to the fourth, fifth, seventh, and eighth cranial nerves as well as the superior petrosal sinus and the petrosal vein, while ensuring complete removal of the tumor (Fig. 2 ). Once the tumor is resected, the tumor bed is irrigated, and Meckel’s cave is filled with hemostatic gelatin sponge to prevent small venous bleeding from the cavernous sinus and postoperative adhesions. ESM.2 Radical removal of a right-sided type C2 trigeminal schwannoma (case 18). An EA-LSRA was done. The operation was uneventful and total resection was achieved. RESULTS Our study included 19 patients, one of whom had a previous surgery and one who underwent radiosurgery at another clinic. Of these, 13 (68.4%) were female and 6 (31.6%) were male. The mean age was 37.5 years (range 15–77 years). Thirteen (68.4%) underwent the EA-PEA and 6 (31.6%) had EA-LSRA. Five had a type A lesion, 1 a type B, 7 type C1, 5 type C2, and 1 type D. The location of the lesions, their volume in each fossa, and the selected surgical approaches are shown in Table 2 . Table 2 Characteristics of the patients Case no. Age, sex Cavernous sinus invasion Brainstem compression Tumor classification (type) Extracranial volume (cm 3 ) Middle fossa volume (cm 3 ) Posterior fossa volume (cm 3 ) Total volume (cm 3 ) Approach Resection after endoscopic visualization 1 39,F No Yes C1 - 9.77 3.01 12.78 EA-PEA GTR 2 29,F Yes Yes C1 - 27.15 19.59 46.74 EA-PEA GTR 3 54,M Yes No A - 16.78 - 16.78 EA-PEA GTR 4 56,F Yes Yes C2 - 11.56 20.86 32.42 EA-LSRA GTR 5 40,M Yes Yes C1 - 16.55 4.87 21.42 EA-PEA Near total 6 30,M Yes Yes D 19.20 15.38 3.41 37.99 EA-PEA Subtotal 7 38,F No Yes C1 - 4.43 1.05 5.48 EA-PEA GTR 8 31,F No No A 12.15 - 12.15 EA-PEA GTR 9 35,F No No A - 2.71 - 2.71 EA-PEA GTR 10 33,F Yes No C1 - 4.92 0.40 5.32 EA-PEA GTR 11 20,F No No A - 4.15 - 4.15 EA-PEA GTR 12 35,M No No A - 4.14 - 4.14 EA-PEA GTR 13 67,M Yes Yes C1 - 11.87 2.36 14.23 EA-PEA GTR 14 40,F Yes Yes C2 - 1.99 6.42 8.41 EA-RSA Near total 15 77,F Yes Yes C2 - 2.46 8.78 11.24 EA-LSRA GTR 16 30,F No Yes C2 - 4.11 14.81 18.92 EA-LSRA GTR 17 37,F No No C1 - 4.37 0.15 4.52 EA-PEA GTR 18 23,F No Yes C2 - 1.18 8.39 9.57 EA-LSRA GTR 19 15,M No Yes B - - 8.44 8.44 EA-LSRA GTR EA-PEA: endoscope-assisted pterional epidural approach, EA-LSRA: endoscope-assisted lateral suboccipital retrosigmoid approach, GTR: gross total resection Signs and Symptoms Eleven patients had facial numbness, three had facial paresthesia, and 1 had masticatory weakness. Three patients had facial pain but only 1 had a definite trigeminal neuralgia, which occurred after Gamma Knife radiosurgery. Two patients came to us with left hemiparesis, 1 of whom had left hemiparesis and facial numbness and the other who had left hemiparesis and progressive sensorineural hearing loss. One patient with peripheral facial paresis also had a swallowing disorder and diplopia. Two had cerebellar signs and 7 had lower cranial nerve deficits. The patient operated on at another institution had left facial hypoesthesia with a right deviated uvula. The most common sign among all patients was facial numbness (57.9%), followed by headache and nausea (31.6%). Table 3 lists the clinical findings of the patients. Table 3 Preoperative clinical findings Preoperative Findings Number of cases (N = 19) Percentage (%) Facial numbness 11 57.9 Headache, nausea 6 31.6 Facial pain 3 15.8 Facial paresthesia 3 15.8 Swallowing disorders 2 10.5 Cerebellar signs 2 10.5 Hemiparesis 2 (left) 10.5 Tinnitus 1 Hearing loss 1 5.3 Cranial nerve deficits 2 1 5.3 3 - 4 - 6 1 5.3 7/8 2 10.5 9–12 3 15.8 Surgical Outcomes Gross total resection was accomplished in 16 patients (84.2%). Near-total resection was achieved in 2 (10.5%), and subtotal resection in 1 (5.3%). During surgery in 5 patients, tumor remnants that were not visible through the microscope were detected with endoscope visualization. Once found, the tumor remnants were totally resected with the microscope or under endoscopic visualization. Using the endoscope after microsurgery, we increased the rate of gross total resection. Postoperative improvement was seen in the patients with hemiparesis, masticatory weakness, and a swallowing disorder. However, an increase in facial hypoesthesia was noted in all patients during the early postoperative period. Additionally, the patient experiencing trigeminal neuralgia after Gamma Knife radiosurgery found relief after the microsurgery. (See the EA-PEA technique for case 13 in Supplemental Video 1 and the EA-LSRA for case 18 in Supplemental Video 2.) No additional neurological deficits or CSF leakage were encountered in the postoperative period. During follow-up, there were no instances of tumor regrowth. In 2 patients with near total resection, tumor remnants not noticed even with the endoscope during surgery were seen on 3-T MRI in the early postoperative period. In one patient, the tumor was left in the infratemporal fossa. However, lesions that are not completely removed are not considered as limitations of the approach. If we had been using intraoperative MRI at that time, we believe we would have noticed the lesion in the infratemporal fossa and resected the residual. Three patients with residual lesions were not referred for postoperative adjuvant radiosurgery but only observed and no tumor regrowth occurred. The cranial nerves and petrosal vein were preserved in all patients. Illustrative cases for types A, B, C1, and C2 appear in Figs. 3 through 6 , respectively. DISCUSSION Comprehensive anatomical knowledge of the trigeminal nerve is needed to understand the clinical presentation of patients with trigeminal schwannomas. Usually, the trigeminal nerve is evaluated in four parts: its course along the brain stem, the cisternal segment (cerebellopontine cistern), the Meckel’s cave segment, and peripheral divisions.[10] Trigeminal schwannomas may arise from any nerve segment [2, 3, 8, 29] and these tumors are usually classified based on the location from which they originate. In 1936, Krayenbühl[30] divided these tumors into two categories: those that arise from the Gasserian ganglion and those that come from the nerve roots. In 1955, Jefferson[2] classified trigeminal schwannomas into three groups: Group A originated from the Gasserian ganglion and the tumor was located in the middle fossa, Group B originated from the root and the tumor was located in the posterior fossa, and Group C was located in both the middle and posterior fossae and was a dumbbell or hourglass shape. With the advancement of surgical techniques, pioneers have since modified and enhanced these traditional classifications to determine the best surgical strategy for total resection.[5, 6, 9, 25, 31] Because of the deep-seated location of the tumor and the relationship with neurovascular structures, approach-related complications can be encountered during surgery.[5, 13] The implementation of our classification system, which is based on the principles of the Jefferson classification, facilitates the choice of surgical approach for each type of lesion. These modifications present a simpler, more comprehensible, and practical classification system for determining the most suitable surgical approach based on the tumor's location. A TSch arises from a limited number of trigeminal nerve fibers and can be distinguished from normal fibers. Preserving the arachnoid layer surrounding the tumor during resection helps protect normal trigeminal nerve fibers and facilitates complete removal without injuring these normal fibers.[16, 26, 27] Achieving total resection is the primary objective, as the recurrence rate is relatively higher when residual tumor remains after surgery.[4, 6, 32] However, removing these tumors is challenging because of their deep-seated location and their extension into multiple cranial fossae. Several surgical approaches have been used to remove trigeminal schwannomas. Dolenc operated on 40 patients using frontotemporal epidural approaches.[8] In his approach, for tumors confined to the cavernous sinus, an orbitotomy is done followed by unroofing of the sphenoid wing and removing the anterior clinoid process. If the tumor extends to both sides of the petrous apex, the petrous apex is drilled off after the superior petrosal sinus is coagulated, thereby combining both fossae by dissecting the tentorium. For lesions with large extensions into the posterior fossa, extensive dural retraction may lead to geniculate ganglion injury, with 15% of cases not covered by bone.[33] We believe that using the EA-LSRA to preserve facial nerve function in patients with C2 lesions is more convenient. Fukaya and colleagues operated on 47 patients using an anterior transpetrosal approach with an anterior petrosectomy or a subtemporal intradural approach or their modifications, depending on the tumor location, including lesions in posterior fossa.[9] After a petrosectomy, they coagulated the superior petrosal sinus and cut the tentorium to combine the fossae. In addition, they carried out a zygomatic osteotomy if necessary to improve the exposure. Nevertheless, tumors with a large extension into the posterior fossa cannot be resected via the middle fossa through Meckel's cave, even when it is expanded.[14, 31] For lesions predominantly located in the posterior fossa (type B and C2) or for lesions equally distributed in the middle and posterior fossa, we believe that the EA-LSRA provides a safer working zone through Meckel's cave to resect lesions in the middle fossa. This approach offers early visualization of the cranial nerves and the brain stem, ensuring that the integrity of the fifth, seventh, and eighth cranial nerves is preserved, as well as the superior petrous sinus and petrous vein. Additionally, preserving the arachnoid layer surrounding the tumor protects the third and fourth cranial nerves and the cavernous sinus during resection in the middle fossa during the EA-LSRA and minimizes the risk of postoperative CSF leakage. Samii and associates[25] retrospectively evaluated 20 patients who underwent different approaches according to their proposed classification and operated on eight patients via the retrosigmoid approach with suprameatal drilling to enlarge the access to Meckel’s cave. In four patients, they used the endoscope to detect any residue. For lesions with middle fossa extensions beyond the posterior paracavernous region, they preferred the retrosigmoid intradural suprameatal approach combined with the subtemporal approach if needed. In our case series, endoscope assistance helps avoid the need for combined approaches or additional extensive bone drilling. Al-Mefty and colleagues[14] operated on 25 patients with trigeminal schwannomas. In 14, they used the zygomatic middle fossa approach. For the other 11, a variety of approaches was used. In the zygomatic middle fossa approach, they removed the posterior fossa extension of the tumor through Meckel’s cave with or without expanding it and without sectioning the tentorium or drilling the petrous apex. However, in patients with large caudal extensions under the seventh and eighth cranial nerves in the posterior fossa, a presigmoid transpetrosal approach was done. Our study included only two approaches (EA-PEA and EA-LSRA), which were chosen according to our modified Tsch classification, and the lesions were removed in a single approach. In addition, the endoscope was used in all patients. Recent advancements in pure endoscopic surgery have suggested a more minimally invasive approach for tumors in different fossae.[20, 34–36] However, tumors with posterior fossa involvement present significant limitations for pure endoscopic surgery compared to microsurgical approaches. The total resection rate is lower for tumors predominantly located in the posterior fossa.[20, 21, 37] Some reports suggest using microsurgical techniques for lesions located in the posterior fossa after endoscopic endonasal surgery because of inadequate surgical manipulation and exposure.[34, 35, 37, 38] Additionally, Wu and colleagues proposed using a single-staged endoscopic trans-Meckel approach combined with a transclival approach for tumors equally located in both middle and posterior fossae, but they recommend a transcranial approach for tumors predominantly in the posterior fossa.[39] Since complete resection is essential to prevent tumor regrowth,[4, 8, 22, 40] the microsurgical approach is considered superior for tumors predominantly located in the posterior fossa. In addition, complications associated with pure endoscopic approaches, such as postoperative CSF leakage,[39] corneal keratopathy,[35, 37] abducens injury,[35] or destruction of the normal nasal cavity, should be kept in mind.[21] However, in patients in whom the tumor is predominantly located in the posterior fossa with expansion into Meckel’s cave, gross total resection can be achieved through endoscope-assisted microsurgical posterior fossa approaches. The use of an endoscope can detect tumor residue that is not noticeable with a microscope and provides a larger field of vision and exposure, facilitating the use of different angled endoscopes through Meckel’s cave. However, failing to locate extracranial extensions of a lesion is still a limitation of endoscopic visualization, as we experienced in case 6. Besides microsurgery and endoscopic approaches, stereotactic radiosurgery has been advocated as a safe and effective treatment method.[41–43] However, tumor expansion and radiosurgery-related symptoms such as facial pain or trigeminal neuralgia may occur after radiosurgery,[31, 43] and complications can arise in patients who undergo surgery after Gamma Knife radiosurgery because of cranial nerve adhesions caused by the radiation.[9] The primary reason to operate on our one patient was not because of tumor size but because severe trigeminal neuralgia appeared after radiosurgery. Since trigeminal schwannomas are benign lesions that can be cured through complete resection, the initial treatment, especially for younger patients, should be surgical resection, as pointed out by Fukaya and colleagues.[9] In addition, patients with symptoms caused by mass effect on the brain stem should be relieved in a short period of time. We believe that Gamma Knife therapy can serve as an adjuvant, especially in older patients, if the residual tumor grows. For younger patients, we prefer additional microsurgical intervention for a growing residual tumor. For patients with asymptomatic or smaller tumors, follow-up without intervention can be considered. Our surgical philosophy for trigeminal schwannoma relies on avoiding extensive skull-base approaches. Instead, we make use of Meckel’s cave, which creates a natural pathway between the middle and posterior fossae when expanded by the lesion.[44] For lesions located predominantly in the middle fossa, we depend on Dolenc’s epidural approach.[8] However, we refrain from using an orbitotomy, clinoidectomy, or anterior petrosectomy and enlarging the foramen ovale or rotundum. Additionally, we do not visualize the greater superficial petrosal nerve or internal carotid artery in the petrous bone, thereby reducing the risk of complications caused by injury to these structures. If the tumor is predominantly in the posterior fossa, we take a conventional retrosigmoid approach with endoscope assistance and can excise any remaining tumor in the middle fossa through Meckel’s cave without suprameatal drilling or a petrosectomy. Using endoscopes with different angles allows us to achieve the goal of total resection without additional bone removal, helping to prevent complications associated with extensive skull-base drilling. None of our patients experienced postoperative hearing loss or CSF leakage. Furthermore, by avoiding dissection of the tentorium, we preserved the superior petrous sinus and did not coagulate the petrous vein in any of the patients. Consequently, complications related to vein coagulation were avoided. [45] CONCLUSION Our study demonstrates that the EA-PEA or EA-LSRA can be sufficient to achieve gross total resection of complex trigeminal schwannomas and enables surgery through Meckel's cave for tumors that have expanded into the middle and posterior fossae as well as those with extracranial extensions. The proposed classification system is helpful for determining the most appropriate approach to the lesion. Additionally, endoscope assistance helps avoid the extensive skull-base approach and complications related to a skull-base osteotomy and tentorial dissection. Using the endoscope after microsurgical resection helps to detect and resect residual tumor in blind spots and increases the total resection rate. Declarations ACKNOWLEGMENTS The authors thank Julie Yamamoto and Daniel Yamamoto for editing the text and Gökhan Canaz for artistic illustrations (Figures 1 and 2). CONFLICT OF INTEREST STATEMENT The authors have no personal, financial, or institutional interest in this article. AUTHOR CONTRIBUTIONS All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Berk Burak Berker, Abuzer Gungor, Yücel Doğruel and Serdar Rahmanov. The first draft of the manuscript was written by Berk Burak Berker, Abuzer Güngör, Yücel Doğruel, Uğur Türe and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Ethics approval and consent to participate This retrospective study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Yeditepe University review boards approved this study. Written informed consent was obtained from all individual participants included in the study and all enrolled patients or their families before conducting this clinical study. We followed the principle of confidentiality and respected any wishes of the patients. Funding No funding or financial support during the preparation of this study. References McCormick PC, Bello JA, Post KD. Trigeminal schwannoma. Surgical series of 14 cases with review of the literature. J Neurosurg 1988; 69: 850–860. JEFFERSON G. The trigeminal neurinomas with some remarks on malignant invasion of the gasserian ganglion. Clin Neurosurg 1953; 1: 11–54. Lesoin F, Rousseaux M, Villette L, et al. Neurinomas of the trigeminal nerve. Acta Neurochir (Wien) 1986; 82: 118–122. Pollack IF, Sekhar LN, Jannetta PJ, et al. Neurilemomas of the trigeminal nerve. J Neurosurg 1989; 70: 737–745. Samii M, Migliori MM, Tatagiba M, et al. Surgical treatment of trigeminal schwannomas. J Neurosurg 1995; 82: 711–718. Ramina R, Mattei TA, Sória MG, et al. Surgical management of trigeminal schwannomas. Neurosurg Focus 2008; 25: 1–9. Yasui T, Hakuba A, Kim SH, et al. Trigeminal neurinomas: Operative approach in eight cases. J Neurosurg 1989; 71: 506–511. Dolenc V V. : Acta Frontotemporal Epidural Approach to Trigeminal Neurinomas. 1994; 55–65. Fukaya R, Yoshida K, Ohira T, et al. Trigeminal schwannomas: Experience with 57 cases and a review of the literature. Neurosurg Rev 2011; 34: 159–171. Joo W, Yoshioka F, Funaki T, et al. Microsurgical anatomy of the trigeminal nerve. Clin Anat 2014; 27: 61–88. Sabanci PA, Batay F, Civelek E, et al. Meckel’s cave. World Neurosurg 2011; 76: 335–341. Bal J, Bruneau M, Berhouma M, et al. Management of non-vestibular schwannomas in adult patients: a systematic review and consensus statement on behalf of the EANS skull base section Part II: Trigeminal and facial nerve schwannomas (CN V, VII). Acta Neurochir (Wien) 2022; 164: 299–319. Yaşargil M. Microneurosurgery-Vol. IV B, Microsurgery of CNS Tumors Instrumentation and Equipment, Laboratory Training, Surgical Approaches, Strategies, Tactics and Techniques, Surgery and Results of Extrinsic and Intrinsic Tumors,Interventional Neuroradiology, Neuro . 1996. Al-Mefty O, Ayoubi S, Gaber E. Trigeminal schwannomas: Removal of dumbbell-shaped tumors through the expanded Meckel cave and outcomes of cranial nerve function. J Neurosurg 2002; 96: 453–463. Aftahy AK, Groll M, Barz M, et al. Surgical outcome of trigeminal schwannomas. Cancers (Basel) 2021; 13: 1–16. Goel A, Muzumdar D, Raman C, et al. Trigeminal neuroma: Analysis of surgical experience with 73 cases. Neurosurgery 2003; 52: 783–790. Wu EM, Sun MZ, Khan NR, et al. Combined Transcavernous and Anterior Petrosectomy [Kawase] Approach to a Trigeminal Schwannoma: 2-Dimensional Operative Video. Oper Neurosurg (Hagerstown, Md) 2023; 25: e150. Frazier CH. An operable tumor involving the gasserian ganglion. Am J Med Sci 1918; 156: 483–490. Schisano G, Olivecrona H. Neurinomas of the Gasserian ganglion and trigeminal root. J Neurosurg 1960; 17: 306–322. Raza SM, Amine MA, Anand V, et al. Endoscopic Endonasal Resection of Trigeminal Schwannomas. Neurosurg Clin N Am 2015; 26: 473–479. Park HH, Hong SD, Kim YH, et al. Endoscopic transorbital and endonasal approach for trigeminal schwannomas: a retrospective multicenter analysis (KOSEN-005. J Neurosurg 2020; 133: 467–476. Taha JM, Tew JM, Van Loveren HR, et al. Comparison of conventional and skull base surgical approaches for the excision of trigeminal neurinomas. J Neurosurg 1995; 82: 719–725. Tomio R, Horiguchi T, Borghei-Razavi H, et al. Anterior transpetrosal approach: experiences in 274 cases over 33 years. Technical variations, operated patients, and approach-related complications. J Neurosurg 2022; 136: 413–421. Giammattei L, Passeri T, Abbritti R, et al. Surgical morbidity of the extradural anterior petrosal approach: the Lariboisière experience. J Neurosurg 2023; 138: 276–286. Samii M, Alimohamadi M, Gerganov V. Endoscope-assisted retrosigmoid intradural suprameatal approach for surgical treatment of trigeminal schwannomas. Oper Neurosurg 2014; 10: 565–575. KEY, A.N., RETZIUS G. Studies in der Anatomic des Nerven Systems und des Bindegewebes, 2, Stockholm, Samson and Wallin, 102. 1876. Yaşargil MG. Microsurgical Anatomy of the Basal Cisterns and Vessels of the Brain, Diagnostic Studies, General Operative Techniques and Pathological Considerations of the Intracranial Aneurysms . thieme, 1984. Gonzalez-Lopez P, Harput M V, Türe H, et al. Efficacy of Placing a Thin Layer of Gelatin Sponge Over the Subdural Space During Dural Closure in Preventing Meningo-Cerebral Adhesion. World Neurosurg 2015; 83: 93–101. Nager GT. Neurinomas of the trigeminal nerve. Am J Otolaryngol 1984; 5: 301–333. KRAYENBÜHL H. PRIMARY TUMOURS OF THE ROOT OF THE FIFTH CRANIAL NERVE: THEIR DISTINCTION FROM TUMOURS OF THE GASSERIAN GANGLION1. Brain 1936; 59: 337–352. Wanibuchi M, Fukushima T, Zomordi AR, et al. Trigeminal schwannomas: skull base approaches and operative results in 105 patients. Neurosurgery 2012; 70: 132–144. Konovalov AN, Spallone A, Mukhamedjanov DJ, et al. Trigeminal neurinomas. A series of 111 surgical cases from a single institution. Acta Neurochir (Wien) 1996; 138: 1027–1035. Rhoton AL, Pulec JL, Hall GM, et al. Absence of bone over the geniculate ganglion. J Neurosurg 1968; 28: 48–53. Kassam AB, Prevedello DM, Carrau RL, et al. The front door to Meckel’s cave: An anteromedial corridor via expanded endoscopic endonasal approach-technical considerations and clinical series. Neurosurgery 2009; 64: 71–83. Raza SM, Donaldson AM, Mehta A, et al. Surgical management of trigeminal schwannomas: Defining the role for endoscopic endonasal approaches. Neurosurg Focus 2014; 37: 1–9. Agosti E, Alexander AY, Choby G, et al. Combined endoscopic endonasal transpterygoid and sublabial transmaxillary approaches for a large infratemporal fossa trigeminal schwannoma. Acta Neurochir (Wien) 2022; 164: 2525–2531. Shin SS, Gardner PA, Stefko ST, et al. Endoscopic endonasal approach for nonvestibular schwannomas. Neurosurgery 2011; 69: 1046–1057. Yang L, Hu L, Zhao W, et al. Endoscopic endonasal approach for trigeminal schwannomas: our experience of 39 patients in 10 years. Eur Arch Oto-Rhino-Laryngology 2018; 275: 735–741. Wu X, Xie SH, Tang B, et al. Single-stage endoscopic endonasal approach for the complete removal of trigeminal schwannomas occupying both the middle and posterior fossae. Neurosurg Rev 2021; 44: 607–616. Bloch DC, Oghalai JS, Jackler RK, et al. The fate of the tumor remnant after less-than-complete acoustic neuroma resection. Otolaryngol neck Surg Off J Am Acad Otolaryngol Neck Surg 2004; 130: 104–112. Hasegawa T, Kida Y, Yoshimoto M, et al. Trigeminal schwannomas: results of gamma knife surgery in 37 cases. J Neurosurg 2007; 106: 18–23. Phi JH, Paek SH, Chung H-T, et al. Gamma Knife surgery and trigeminal schwannoma: is it possible to preserve cranial nerve function? J Neurosurg 2007; 107: 727–732. Sheehan J, Yen CP, Arkha Y, et al. Gamma knife surgery for trigeminal schwannoma. J Neurosurg 2007; 106: 839–845. Malhotra A, Tu L, Kalra VB, et al. Neuroimaging of Meckel’s cave in normal and disease conditions. Insights Imaging 2018; 9: 499–510. Koerbel A, Gharabaghi A, Safavi-Abbasi S, et al. Venous complications following petrosal vein sectioning in surgery of petrous apex meningiomas. Eur J Surg Oncol 2009; 35: 773–779. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5211321","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":370947894,"identity":"78617252-aa57-4421-8433-69a2fc6b8f70","order_by":0,"name":"Berk Burak Berker","email":"","orcid":"","institution":"Hatay Training and Research Hospital","correspondingAuthor":false,"prefix":"","firstName":"Berk","middleName":"Burak","lastName":"Berker","suffix":""},{"id":370947895,"identity":"ffe7e58a-8159-4be4-a939-c6d49e8bce09","order_by":1,"name":"Abuzer Güngör","email":"","orcid":"","institution":"Istinye University","correspondingAuthor":false,"prefix":"","firstName":"Abuzer","middleName":"","lastName":"Güngör","suffix":""},{"id":370947896,"identity":"dbd0f7b0-89cd-41a2-baf7-b1af7850a217","order_by":2,"name":"Yücel Doğruel","email":"","orcid":"","institution":"Izmir Tepecik Eğitim ve Araştırma Hastanesi","correspondingAuthor":false,"prefix":"","firstName":"Yücel","middleName":"","lastName":"Doğruel","suffix":""},{"id":370947897,"identity":"517b465f-6ad0-4037-b8b8-ce9998ef824b","order_by":3,"name":"Serdar Rahmanov","email":"","orcid":"","institution":"Yeditepe University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Serdar","middleName":"","lastName":"Rahmanov","suffix":""},{"id":370947898,"identity":"55b2c51c-29d1-4750-b319-4ced1ccba70a","order_by":4,"name":"Hatice Türe","email":"","orcid":"","institution":"Yeditepe University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Hatice","middleName":"","lastName":"Türe","suffix":""},{"id":370947899,"identity":"9ab64ee9-6a88-44a1-a9e3-5058c61ba3fe","order_by":5,"name":"Ugur Türe","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAqklEQVRIiWNgGAWjYDCCA2DShoFBgngtzCAyjXQth0nQwnf7/DHpiorzif2zmw8+YKixiSaoRfJcMpvkmTO3E2fcOZZswHAsLbeBkBaDM8xsko1ttxMbbuSYSTA2HCZWy79zifNJ1NJwIHED0VokzzAbWzYcSzbeeCMt2SCBGL/wnWF8eLOhxk523o3kgw8+1NgQ1gIDjmCVCcQqBwF7UhSPglEwCkbBCAMAuXZBPCpynpIAAAAASUVORK5CYII=","orcid":"","institution":"Yeditepe University School of Medicine","correspondingAuthor":true,"prefix":"","firstName":"Ugur","middleName":"","lastName":"Türe","suffix":""}],"badges":[],"createdAt":"2024-10-06 05:23:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5211321/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5211321/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":70287695,"identity":"dc44293c-5fd1-48db-aaa8-1b1c0087c1c0","added_by":"auto","created_at":"2024-12-01 16:53:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":8815191,"visible":true,"origin":"","legend":"\u003cp\u003eAn illustration of the EA-PEA to resect a type C1 trigeminal schwannoma. \u003cstrong\u003eA:\u003c/strong\u003e The upper image shows the location of the lesion in both fossae as seen on an axial section from the top. The outer layer of the lateral wall of the cavernous sinus is separated from the inner layer and the tumor is located between these two layers. The lower image depicts this area after resection of the lesion in the middle fossa. The intact branches of the trigeminal nerve are seen. \u003cstrong\u003eB:\u003c/strong\u003e The perspective from the posterior fossa. The middle fossa and the outer layer of the dura, which is retracted with sutures not a rigid retractor, are shown in the blurred area. The * indicates Meckel’s cave. Part of the lesion in the posterior fossa was observed with an endoscope through this structure. \u003cstrong\u003eC:\u003c/strong\u003e The perspective from the posterior fossa after the resection of residual tumor in this space with endoscopic assistance. Resection was completed without expanding Meckel’s cave, a skull-base osteotomy, or tentorial dissection. The trigeminal nerve is flattened and seen as separate fibers due to the mass effect of the lesion. However, the integrity of the fibers is preserved.\u003c/p\u003e","description":"","filename":"figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/d7cb50da78b7a517ebacaa3b.png"},{"id":70287721,"identity":"7e1a78fe-5a3c-48f3-9308-0707960b571f","added_by":"auto","created_at":"2024-12-01 16:53:35","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":9294843,"visible":true,"origin":"","legend":"\u003cp\u003eAn illustration of the\u003cstrong\u003e \u003c/strong\u003eEA-LSRA to resect a type C2 trigeminal schwannoma. \u003cstrong\u003eA:\u003c/strong\u003e The upper image shows the location of the lesion from the top. The lower image shows the middle fossa part of the lesion, which was resected via endoscope assistance through Meckel’s cave. Note the mass effect of the lesion on the brain stem. \u003cstrong\u003eB: \u003c/strong\u003eThe perspective from the middle fossa. Residual tumor in the middle fossa was observed with the endoscope through Meckel’s cave after the lesion’s posterior fossa portion was resected. \u003cstrong\u003eC\u003c/strong\u003e: The perspective from the middle fossa after residual tumor in this structure was resected with endoscope assistance without expanding Meckel’s cave, suprameatal drilling, or tentorial dissection. As illustrated, the superior petrous sinus and petrous vein are preserved during the approach. The trigeminal nerve is flattened and appears as separate fibers due to the mass effect of the lesion. However, the integrity of the fibers is preserved.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/44ecb3f6f22fa003acea37fc.png"},{"id":70287696,"identity":"a8cdcdad-52eb-49a0-bb3a-44588d4bc4e5","added_by":"auto","created_at":"2024-12-01 16:53:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2544493,"visible":true,"origin":"","legend":"\u003cp\u003eA 31-year-old female (case 8) had been experiencing headaches and trigeminal neuralgia after Gamma Knife radiosurgery. \u003cstrong\u003eA:\u003c/strong\u003e Preoperative axial, coronal, and sagittal T1-weighted MRI with gadolinium revealed a lesion in the middle fossa and classified as a type A tumor. An EA-PEA was performed without complications, resulting in complete removal of the lesion. Histopathological examination confirmed the lesion as a trigeminal schwannoma. \u003cstrong\u003eB:\u003c/strong\u003ePostoperative axial, coronal, and sagittal T1-weighted images with gadolinium obtained 3 months after surgery showed gross total resection. The patient’s trigeminal neuralgia disappeared after resection. (L) represents the patient's left side.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/9e0a6abc703e27b402fe9000.png"},{"id":70287698,"identity":"efc63f37-5f69-4218-a7ce-94e967a0de76","added_by":"auto","created_at":"2024-12-01 16:53:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":4882656,"visible":true,"origin":"","legend":"\u003cp\u003eA 15-year-old male (case 19) had been experiencing headaches, facial numbness and nausea. \u003cstrong\u003eA: \u003c/strong\u003ePreoperative axial, coronal, and sagittal T1-weighted MRI with gadolinium revealed a lesion with components in the posterior fossa. The lesion caused major brainstem compression and was classified as a type B tumor. An EA-LSRA was done without complications, resulting in complete removal of the lesion. Histopathological examination confirmed the lesion as a trigeminal schwannoma. \u003cstrong\u003eB:\u003c/strong\u003ePostoperative axial, coronal, and sagittal T1-weighted images with gadolinium obtained 3 months after surgery showed gross total resection. (L) represents the patient's left side.\u003c/p\u003e","description":"","filename":"figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/7e8df93a66445e43e207fe14.png"},{"id":70287718,"identity":"e9719b0f-2c2d-40d3-a78e-0a7ee8ad15fc","added_by":"auto","created_at":"2024-12-01 16:53:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2464894,"visible":true,"origin":"","legend":"\u003cp\u003eA 29-year-old female (case 2) had been experiencing tinnitus, vertigo, and nausea. \u003cstrong\u003eA:\u003c/strong\u003e Preoperative axial, coronal, and sagittal T1-weighted MRI with gadolinium revealed a lesion in the middle and posterior fossae. The lesion caused compression of the brain stem and fourth ventricle and also infiltrated the cavernous sinus. It was classified as type C1. An EA-PEA was performed without complications, resulting in complete removal of the lesion. Histopathological examination confirmed the lesion as a trigeminal schwannoma. \u003cstrong\u003eB:\u003c/strong\u003ePostoperative axial, coronal, and sagittal T1-weighted images with gadolinium obtained 3 months after surgery showed gross total resection. (L) represents the patient's left side.\u003c/p\u003e","description":"","filename":"figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/2979c906f3f13e232d97737c.png"},{"id":70287829,"identity":"9fd20e7b-5fbd-4a2e-8d35-dacb2b45c160","added_by":"auto","created_at":"2024-12-01 17:01:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2867416,"visible":true,"origin":"","legend":"\u003cp\u003eA 30-year-old female (case 16) had been experiencing facial numbness and hypoesthesia. \u003cstrong\u003eA:\u003c/strong\u003ePreoperative axial, coronal, and sagittal T1-weighted MRI with gadolinium revealed a lesion with components in the middle and posterior fossae. The lesion caused major brainstem compression and was classified as type C2. An EA-LSRA was done without complications, resulting in complete removal of the lesion. Histopathological examination confirmed the lesion as a trigeminal schwannoma. \u003cstrong\u003eB:\u003c/strong\u003ePostoperative axial, coronal, and sagittal T1-weighted images with gadolinium obtained 3 months after surgery showed gross total resection. (L) represents the patient's left side.\u003c/p\u003e","description":"","filename":"figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/5af1431cf9befc13211be149.png"},{"id":74560620,"identity":"27261fc4-8c77-4cea-8204-42708054795b","added_by":"auto","created_at":"2025-01-23 12:47:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":29911171,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/5c7f9b98-729e-4d83-adc3-aa2a39c5e58f.pdf"},{"id":70287790,"identity":"3b138d83-c135-4ffa-9fe7-7c65654147f8","added_by":"auto","created_at":"2024-12-01 16:53:47","extension":"mp4","order_by":11,"title":"","display":"","copyAsset":false,"role":"supplement","size":967133089,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementalVideo1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/616f80f8b2a1b267ac4e5cfc.mp4"},{"id":70287791,"identity":"8efffa20-08e5-40ce-b5c9-ba258263fd05","added_by":"auto","created_at":"2024-12-01 16:53:53","extension":"mp4","order_by":12,"title":"","display":"","copyAsset":false,"role":"supplement","size":748894442,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementalVideo2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-5211321/v1/5b8315343f759ab9dc266b2e.mp4"}],"financialInterests":"No competing interests reported.","formattedTitle":"Endoscope-assisted trigeminal schwannoma resection without extensive skull-base drilling ","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eTrigeminal schwannoma (TSch) is a rare lesion and usually considered to be benign. These tumors comprise 0.07\u0026ndash;0.36% of intracranial tumors and 0.8\u0026ndash;8% of intracranial schwannomas.[1\u0026ndash;5] Surgical resection is the optimal treatment and these tumors can be cured with total resection.[6\u0026ndash;8] As a TSch can originate from the trigeminal root, ganglion, or peripheral division of the nerve, these tumors have the potential to expand into different compartments: the posterior fossa (cerebellopontine angle), intradural space (Meckel\u0026rsquo;s cave), or extracranial spaces such as the orbita, pterygopalatine fossa, or infratemporal fossa.[9\u0026ndash;12]However, surgery for these lesions is challenging because of their complicated incursion into different fossae and their close relations with vital structures.[13\u0026ndash;15]\u003c/p\u003e \u003cp\u003eSeveral surgical strategies for the complete removal of these tumors have been described.[8, 9, 14, 16, 17] Since the first case describing resection of a lesion in Meckel\u0026rsquo;s cave, total resection rates have increased while complication rates have decreased with the development of microsurgical skull-base techniques.[8, 18, 19] In addition to the use of microsurgical techniques, successful resection rates have been reported for a TSch located in intra- and extradural spaces because of improvements in endoscopic techniques. However, purely endoscopic approaches are not as successful as microscopic techniques for lesions located in or spreading to the posterior fossa.[20, 21]To resect a TSch that extends into multiple fossae with skull-base approaches, extensive bone removal or dissection of vascular structures is necessary to obtain adequate exposure.[8, 9, 22] However, serious complications can result from these complex approaches.[23, 24]\u003c/p\u003e \u003cp\u003eIn this study, we show that successful resection of a TSch is possible with the endoscope-assisted pterional epidural approach (EA-PEA) and the endoscope-assisted lateral suboccipital retrosigmoid approach (EA-LSRA). With endoscope assistance, we can harness the advantages of both microsurgical and endoscopic techniques, addressing the problems related to intraoperative visualization in the microsurgical procedures and effectively removing any tumor remnants noticed during endoscopy. Moreover, this technique allows total resection without additional bone removal or a petrosectomy through the natural pathway created by Meckel\u0026rsquo;s cave between the middle and posterior fossae. Additionally, we describe a modified classification for these lesions based on Jefferson\u0026rsquo;s classification system for trigeminal schwannomas.\u003c/p\u003e"},{"header":"MATERIAL AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ePatient Data and Outcome Assessment\u003c/h2\u003e \u003cp\u003eA series of 19 patients with TSch in different cerebral fossae were operated on via the EA-PEA or EA-LSRA in our institution by the senior author (UT) from April 2007 through May 2023. These cases were retrospectively evaluated. Among these patients, 13 underwent EA-PEA and 6 underwent EA-LSRA. Of these 6 patients, 3 underwent EA-LSRA in the lateral position and the remaining 3 in the semi-lateral position.\u003c/p\u003e \u003cp\u003eEighteen patients underwent surgery for the first time. However, one of these patients had gamma knife radiosurgery at another clinic but experienced progressive trigeminal neuralgia and was admitted to our clinic for microsurgical resection. The nineteenth had partial removal of the lesion at another institution. This patient was admitted to our clinic because of regrowth and associated symptoms.\u003c/p\u003e \u003cp\u003eNeuroradiological evaluation included preoperative CT scanning, and preoperative, early postoperative (\u0026lt;\u0026thinsp;24 hours), and 3-month postoperative evaluations were done with magnetic resonance imaging (MRI) according to standard imaging protocols. Intraoperative MRI was introduced into our institution in January 2018. After this timepoint, this modality was used routinely. All patients underwent detailed neurological examinations at admission, after surgery, at discharge, and at follow-up. Electromyographic recordings from the seventh and eighth cranial nerves, motor evoked potentials, and somatosensory evoked potentials were obtained for patients with lesions compressing the brain stem.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows our modified classification system, which is based on Jefferson\u0026rsquo;s trigeminal schwannoma classification. In both systems, lesions in the middle fossa are classified as type A. Lesions located in the posterior fossa are type B, and those extending into both fossae are type C. In our modification, lesions predominantly occupying the middle fossa are type C1. Conversely, tumors primarily occupying the posterior fossa are defined as type C2. Those with extracranial components are classified as type D regardless of which fossa they predominantly occupy. The surgical approach for each patient was chosen according to this modified classification.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of Jefferson\u0026rsquo;s classification and our modified classification\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eJefferson Classification\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAuthors\u0026rsquo; Modified Classification Approach\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup A: Lesion occupies the middle fossa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType A: Lesion occupies the middle fossa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup B: Lesion occupies the posterior fossa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType B: Lesion occupies the posterior fossa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eGroup C: Lesion occupies both cerebral fossae\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType C1: Lesion occupies both fossae but lies predominantly in the middle fossa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType C2: Lesion occupies both fossae but lies predominantly in the posterior fossa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType D: Lesion has various extracranial expansions\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe volume of each tumor in each fossa was measured in cubic centimeters (cm\u003csup\u003e3\u003c/sup\u003e) with the Osirix software (Pixmeo, Geneva, Switzerland), and the surgical approach was chosen according to the lesion volume in different fossae. Patients with type A and C1 lesions underwent an EA-PEA, while those with type B and C2 lesions were treated with an EA-LSRA. For patients with type D lesions, the surgical approach was determined based on the tumor volume in the respective fossae. If the tumor volume was higher in the extracranial and middle fossae together, an EA-PEA approach was done. Conversely, if the volume was higher in the posterior fossa, the EA-LSRA was chosen.\u003c/p\u003e \u003cp\u003eResection rates were evaluated as Samii and colleagues carried out in their study.[25] Total removal of the tumor was considered gross total resection. If less than 5% of the tumor remained after surgery, it was considered near total resection. Tumor of greater than 5% remaining was designated subtotal resection.\u003c/p\u003e \u003cp\u003e Written informed consent was obtained from all patients, and the study was approved by our institutional review committee.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSurgical Techniques\u003c/h3\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eEndoscope-Assisted Pterional Epidural Approach\u003c/h2\u003e \u003cp\u003eFor the endoscope-assisted pterional epidural approach (EA-PEA), lumbar drainage is done preoperatively to release cerebrospinal fluid (CSF), which allows the temporal pole to be retracted with minimal risk of damage to brain tissue and to achieve adequate exposure of the tumor. A pterional craniotomy is done and the sphenoid ridge drilled and flattened. The dura is dissected away from both the frontal and temporal sides of the sphenoid ridge. The meningo-orbital band connecting the outer border of the superior orbital fossa and the frontotemporal dura is dissected and incised. The cavernous sinus is exposed extradurally, and the outer layer of the lateral wall of the cavernous sinus is separated from the inner layer, as performed by Dolenc.[8] The outer dural layer is mobilized, providing good exposure without retracting the brain, which is well protected by the preserved outer layer of the dura. Subsequently, the outer dural layer is fixed with tacking sutures without the need for a rigid retractor.\u003c/p\u003e \u003cp\u003eOnce the tumor is visualized in the intradural space, an arachnoid layer is seen surrounding the tumor.[26, 27] Preserving this layer allows tumor removal without opening the cavernous sinus and minimizes the risk of injury to the third, fourth, and sixth cranial nerves located in the lateral wall of the cavernous sinus. After the tumor is accessed and debulked in piecemeal fashion, a micro-Doppler ultrasound (Mizuho America, Inc.) is used to locate the cavernous segment of the internal carotid artery to preserve it.\u003c/p\u003e \u003cp\u003eThe posterior fossa component of a type C1 and D TSch can be totally removed through Meckel\u0026rsquo;s cave without extensive bone drilling including an anterior clinoidectomy or petrosectomy. Moreover, it can be accomplished without enlarging the foramen ovale and rotundum, reducing the risk of CSF leakage postoperatively. The tumor is removed without bipolar coagulation to preserve the integrity of adjacent structures. After excision, which is visualized through the microscope, straight (0-degree angle) and angled (30 and 45 degrees, if needed) endoscopes are used to visualize parts of Meckel\u0026rsquo;s cave and the posterior fossa that may not be visible through the microscope. If any tumor remnants are observed in Meckel\u0026rsquo;s cave or the posterior fossa at this time, they are excised either with a microscope or under endoscopic visualization without dissecting the tentorium. This approach preserves the third, fourth, and sixth cranial nerves, the superior petrosal sinus, and the petrosal vein, while ensuring complete removal of the tumor (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). After the tumor bed is irrigated, Meckel\u0026rsquo;s cave is filled with an absorbable hemostatic gelatin sponge coated with polypeptides (Spongostan; Ethicon, Inc., Somerville, New Jersey) to prevent small venous bleeding from the cavernous sinus. The gelatin sponge also prevents meningocerebral adhesions and does not generate postoperative artifacts on MRI, unlike fat tissue.[28] Before closing, a small incision is made in the dura and normal saline is re-injected into the subdural space to return the dura to its normal state. The incision is then closed and the lumbar drain removed.\u003c/p\u003e \u003cp\u003e \u003cb\u003eESM.1\u003c/b\u003e Radical removal of a right-sided type C1 trigeminal schwannoma (case 13). An EA- PEA was carried out. The operation was uneventful and total resection was achieved.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEndoscope-Assisted Lateral Suboccipital Retrosigmoid Approach\u003c/h3\u003e\n\u003cp\u003eA lateral suboccipital craniotomy with the retrosigmoid approach was done for six patients, with three in a lateral position and three in a semi-lateral position. After January 2018, the semi-lateral position has been used to accommodate intraoperative MRI.\u003c/p\u003e \u003cp\u003eA linear lateral occipital incision is made, followed by a lateral suboccipital craniotomy. Two openings are then created in the dura. The first is placed over the lower aspect of the craniotomy to release CSF from the cisterna magna, relaxing the posterior fossa. The second incision is made 15 mm below the transverse sinus after the exact location of the transverse and sigmoid sinuses are confirmed. Then, the two openings are connected with a curvilinear incision parallel to the sigmoid sinus.\u003c/p\u003e \u003cp\u003eWhen the patient is in the lateral or semi-lateral position, adequate exposure is obtained without rigid retractors through gravitational retraction of the cerebellum. Afterwards, the petrous vein, and the seventh and eighth nerves are identified. Subsequently, the arachnoid layer surrounding the tumor is identified.[26, 27] Preserving this layer allows tumor resection without injury to the roots of the fifth cranial nerve and surrounding structures.\u003c/p\u003e \u003cp\u003eAfter the tumor is debulked, the fourth and fifth nerves are identified. The trigeminal nerve appears as separated fibers and is flattened due to mass effect of the lesion. For types C2 and D, the portion of tumor in the middle fossa is removed through Meckel\u0026rsquo;s cave. As some parts of the tumor in Meckel\u0026rsquo;s cave and the middle fossa are not visualized with the microscope, a 30-degree angled endoscope (or 45 degrees, if needed) is used, and any tumor remnants are removed under the microscope or endoscope visualization, if required, without tentorial dissection or additional bone drilling. This approach preserves hearing and, by preserving the arachnoid layer over the tumor, minimizes the risk of injury to the fourth, fifth, seventh, and eighth cranial nerves as well as the superior petrosal sinus and the petrosal vein, while ensuring complete removal of the tumor (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Once the tumor is resected, the tumor bed is irrigated, and Meckel\u0026rsquo;s cave is filled with hemostatic gelatin sponge to prevent small venous bleeding from the cavernous sinus and postoperative adhesions.\u003c/p\u003e \u003cp\u003e \u003cb\u003eESM.2\u003c/b\u003e Radical removal of a right-sided type C2 trigeminal schwannoma (case 18). An EA-LSRA was done. The operation was uneventful and total resection was achieved.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eOur study included 19 patients, one of whom had a previous surgery and one who underwent radiosurgery at another clinic. Of these, 13 (68.4%) were female and 6 (31.6%) were male. The mean age was 37.5 years (range 15\u0026ndash;77 years). Thirteen (68.4%) underwent the EA-PEA and 6 (31.6%) had EA-LSRA. Five had a type A lesion, 1 a type B, 7 type C1, 5 type C2, and 1 type D. The location of the lesions, their volume in each fossa, and the selected surgical approaches are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of the patients\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCase no.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAge, sex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCavernous sinus invasion\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBrainstem compression\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTumor classification (type)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eExtracranial volume\u003c/p\u003e \u003cp\u003e(cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eMiddle fossa volume (cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003ePosterior fossa volume (cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eTotal volume (cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eApproach\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eResection after endoscopic visualization\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e12.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e27.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e19.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e46.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e54,M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e16.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e16.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e56,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e20.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e32.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-LSRA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40,M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e16.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e21.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eNear total\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30,M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e19.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e15.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e37.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eSubtotal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e5.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e12.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e12.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e2.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e33,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e5.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35,M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e67,M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e14.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e8.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-RSA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eNear total\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e77,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e8.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e11.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-LSRA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e14.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e18.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-LSRA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-PEA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23,F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e8.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e9.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-LSRA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15,M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e8.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e8.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eEA-LSRA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eGTR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"11\"\u003eEA-PEA: endoscope-assisted pterional epidural approach, EA-LSRA: endoscope-assisted lateral suboccipital retrosigmoid approach, GTR: gross total resection\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eSigns and Symptoms\u003c/h2\u003e \u003cp\u003eEleven patients had facial numbness, three had facial paresthesia, and 1 had masticatory weakness. Three patients had facial pain but only 1 had a definite trigeminal neuralgia, which occurred after Gamma Knife radiosurgery. Two patients came to us with left hemiparesis, 1 of whom had left hemiparesis and facial numbness and the other who had left hemiparesis and progressive sensorineural hearing loss. One patient with peripheral facial paresis also had a swallowing disorder and diplopia. Two had cerebellar signs and 7 had lower cranial nerve deficits. The patient operated on at another institution had left facial hypoesthesia with a right deviated uvula. The most common sign among all patients was facial numbness (57.9%), followed by headache and nausea (31.6%). Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e lists the clinical findings of the patients.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePreoperative clinical findings\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreoperative Findings\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNumber of cases (N\u0026thinsp;=\u0026thinsp;19)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePercentage (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFacial numbness\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e57.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeadache, nausea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e31.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFacial pain\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFacial paresthesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSwallowing disorders\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCerebellar signs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHemiparesis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 (left)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTinnitus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHearing loss\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCranial nerve deficits\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7/8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u0026ndash;12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSurgical Outcomes\u003c/h3\u003e\n\u003cp\u003eGross total resection was accomplished in 16 patients (84.2%). Near-total resection was achieved in 2 (10.5%), and subtotal resection in 1 (5.3%). During surgery in 5 patients, tumor remnants that were not visible through the microscope were detected with endoscope visualization. Once found, the tumor remnants were totally resected with the microscope or under endoscopic visualization. Using the endoscope after microsurgery, we increased the rate of gross total resection. Postoperative improvement was seen in the patients with hemiparesis, masticatory weakness, and a swallowing disorder. However, an increase in facial hypoesthesia was noted in all patients during the early postoperative period. Additionally, the patient experiencing trigeminal neuralgia after Gamma Knife radiosurgery found relief after the microsurgery. (See the EA-PEA technique for case 13 in Supplemental Video 1 and the EA-LSRA for case 18 in Supplemental Video 2.)\u003c/p\u003e \u003cp\u003eNo additional neurological deficits or CSF leakage were encountered in the postoperative period. During follow-up, there were no instances of tumor regrowth. In 2 patients with near total resection, tumor remnants not noticed even with the endoscope during surgery were seen on 3-T MRI in the early postoperative period. In one patient, the tumor was left in the infratemporal fossa. However, lesions that are not completely removed are not considered as limitations of the approach. If we had been using intraoperative MRI at that time, we believe we would have noticed the lesion in the infratemporal fossa and resected the residual. Three patients with residual lesions were not referred for postoperative adjuvant radiosurgery but only observed and no tumor regrowth occurred. The cranial nerves and petrosal vein were preserved in all patients. Illustrative cases for types A, B, C1, and C2 appear in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e through \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eComprehensive anatomical knowledge of the trigeminal nerve is needed to understand the clinical presentation of patients with trigeminal schwannomas. Usually, the trigeminal nerve is evaluated in four parts: its course along the brain stem, the cisternal segment (cerebellopontine cistern), the Meckel\u0026rsquo;s cave segment, and peripheral divisions.[10] Trigeminal schwannomas may arise from any nerve segment [2, 3, 8, 29] and these tumors are usually classified based on the location from which they originate. In 1936, Krayenb\u0026uuml;hl[30] divided these tumors into two categories: those that arise from the Gasserian ganglion and those that come from the nerve roots. In 1955, Jefferson[2] classified trigeminal schwannomas into three groups: Group A originated from the Gasserian ganglion and the tumor was located in the middle fossa, Group B originated from the root and the tumor was located in the posterior fossa, and Group C was located in both the middle and posterior fossae and was a dumbbell or hourglass shape. With the advancement of surgical techniques, pioneers have since modified and enhanced these traditional classifications to determine the best surgical strategy for total resection.[5, 6, 9, 25, 31] Because of the deep-seated location of the tumor and the relationship with neurovascular structures, approach-related complications can be encountered during surgery.[5, 13] The implementation of our classification system, which is based on the principles of the Jefferson classification, facilitates the choice of surgical approach for each type of lesion. These modifications present a simpler, more comprehensible, and practical classification system for determining the most suitable surgical approach based on the tumor's location.\u003c/p\u003e \u003cp\u003eA TSch arises from a limited number of trigeminal nerve fibers and can be distinguished from normal fibers. Preserving the arachnoid layer surrounding the tumor during resection helps protect normal trigeminal nerve fibers and facilitates complete removal without injuring these normal fibers.[16, 26, 27] Achieving total resection is the primary objective, as the recurrence rate is relatively higher when residual tumor remains after surgery.[4, 6, 32] However, removing these tumors is challenging because of their deep-seated location and their extension into multiple cranial fossae.\u003c/p\u003e \u003cp\u003eSeveral surgical approaches have been used to remove trigeminal schwannomas. Dolenc operated on 40 patients using frontotemporal epidural approaches.[8] In his approach, for tumors confined to the cavernous sinus, an orbitotomy is done followed by unroofing of the sphenoid wing and removing the anterior clinoid process. If the tumor extends to both sides of the petrous apex, the petrous apex is drilled off after the superior petrosal sinus is coagulated, thereby combining both fossae by dissecting the tentorium. For lesions with large extensions into the posterior fossa, extensive dural retraction may lead to geniculate ganglion injury, with 15% of cases not covered by bone.[33] We believe that using the EA-LSRA to preserve facial nerve function in patients with C2 lesions is more convenient.\u003c/p\u003e \u003cp\u003eFukaya and colleagues operated on 47 patients using an anterior transpetrosal approach with an anterior petrosectomy or a subtemporal intradural approach or their modifications, depending on the tumor location, including lesions in posterior fossa.[9] After a petrosectomy, they coagulated the superior petrosal sinus and cut the tentorium to combine the fossae. In addition, they carried out a zygomatic osteotomy if necessary to improve the exposure. Nevertheless, tumors with a large extension into the posterior fossa cannot be resected via the middle fossa through Meckel's cave, even when it is expanded.[14, 31] For lesions predominantly located in the posterior fossa (type B and C2) or for lesions equally distributed in the middle and posterior fossa, we believe that the EA-LSRA provides a safer working zone through Meckel's cave to resect lesions in the middle fossa. This approach offers early visualization of the cranial nerves and the brain stem, ensuring that the integrity of the fifth, seventh, and eighth cranial nerves is preserved, as well as the superior petrous sinus and petrous vein. Additionally, preserving the arachnoid layer surrounding the tumor protects the third and fourth cranial nerves and the cavernous sinus during resection in the middle fossa during the EA-LSRA and minimizes the risk of postoperative CSF leakage.\u003c/p\u003e \u003cp\u003eSamii and associates[25] retrospectively evaluated 20 patients who underwent different approaches according to their proposed classification and operated on eight patients via the retrosigmoid approach with suprameatal drilling to enlarge the access to Meckel\u0026rsquo;s cave. In four patients, they used the endoscope to detect any residue. For lesions with middle fossa extensions beyond the posterior paracavernous region, they preferred the retrosigmoid intradural suprameatal approach combined with the subtemporal approach if needed. In our case series, endoscope assistance helps avoid the need for combined approaches or additional extensive bone drilling.\u003c/p\u003e \u003cp\u003eAl-Mefty and colleagues[14] operated on 25 patients with trigeminal schwannomas. In 14, they used the zygomatic middle fossa approach. For the other 11, a variety of approaches was used. In the zygomatic middle fossa approach, they removed the posterior fossa extension of the tumor through Meckel\u0026rsquo;s cave with or without expanding it and without sectioning the tentorium or drilling the petrous apex. However, in patients with large caudal extensions under the seventh and eighth cranial nerves in the posterior fossa, a presigmoid transpetrosal approach was done. Our study included only two approaches (EA-PEA and EA-LSRA), which were chosen according to our modified Tsch classification, and the lesions were removed in a single approach. In addition, the endoscope was used in all patients.\u003c/p\u003e \u003cp\u003eRecent advancements in pure endoscopic surgery have suggested a more minimally invasive approach for tumors in different fossae.[20, 34\u0026ndash;36] However, tumors with posterior fossa involvement present significant limitations for pure endoscopic surgery compared to microsurgical approaches. The total resection rate is lower for tumors predominantly located in the posterior fossa.[20, 21, 37] Some reports suggest using microsurgical techniques for lesions located in the posterior fossa after endoscopic endonasal surgery because of inadequate surgical manipulation and exposure.[34, 35, 37, 38] Additionally, Wu and colleagues proposed using a single-staged endoscopic trans-Meckel approach combined with a transclival approach for tumors equally located in both middle and posterior fossae, but they recommend a transcranial approach for tumors predominantly in the posterior fossa.[39] Since complete resection is essential to prevent tumor regrowth,[4, 8, 22, 40] the microsurgical approach is considered superior for tumors predominantly located in the posterior fossa. In addition, complications associated with pure endoscopic approaches, such as postoperative CSF leakage,[39] corneal keratopathy,[35, 37] abducens injury,[35] or destruction of the normal nasal cavity, should be kept in mind.[21] However, in patients in whom the tumor is predominantly located in the posterior fossa with expansion into Meckel\u0026rsquo;s cave, gross total resection can be achieved through endoscope-assisted microsurgical posterior fossa approaches. The use of an endoscope can detect tumor residue that is not noticeable with a microscope and provides a larger field of vision and exposure, facilitating the use of different angled endoscopes through Meckel\u0026rsquo;s cave. However, failing to locate extracranial extensions of a lesion is still a limitation of endoscopic visualization, as we experienced in case 6.\u003c/p\u003e \u003cp\u003eBesides microsurgery and endoscopic approaches, stereotactic radiosurgery has been advocated as a safe and effective treatment method.[41\u0026ndash;43] However, tumor expansion and radiosurgery-related symptoms such as facial pain or trigeminal neuralgia may occur after radiosurgery,[31, 43] and complications can arise in patients who undergo surgery after Gamma Knife radiosurgery because of cranial nerve adhesions caused by the radiation.[9] The primary reason to operate on our one patient was not because of tumor size but because severe trigeminal neuralgia appeared after radiosurgery. Since trigeminal schwannomas are benign lesions that can be cured through complete resection, the initial treatment, especially for younger patients, should be surgical resection, as pointed out by Fukaya and colleagues.[9] In addition, patients with symptoms caused by mass effect on the brain stem should be relieved in a short period of time. We believe that Gamma Knife therapy can serve as an adjuvant, especially in older patients, if the residual tumor grows. For younger patients, we prefer additional microsurgical intervention for a growing residual tumor. For patients with asymptomatic or smaller tumors, follow-up without intervention can be considered.\u003c/p\u003e \u003cp\u003eOur surgical philosophy for trigeminal schwannoma relies on avoiding extensive skull-base approaches. Instead, we make use of Meckel\u0026rsquo;s cave, which creates a natural pathway between the middle and posterior fossae when expanded by the lesion.[44] For lesions located predominantly in the middle fossa, we depend on Dolenc\u0026rsquo;s epidural approach.[8] However, we refrain from using an orbitotomy, clinoidectomy, or anterior petrosectomy and enlarging the foramen ovale or rotundum. Additionally, we do not visualize the greater superficial petrosal nerve or internal carotid artery in the petrous bone, thereby reducing the risk of complications caused by injury to these structures. If the tumor is predominantly in the posterior fossa, we take a conventional retrosigmoid approach with endoscope assistance and can excise any remaining tumor in the middle fossa through Meckel\u0026rsquo;s cave without suprameatal drilling or a petrosectomy. Using endoscopes with different angles allows us to achieve the goal of total resection without additional bone removal, helping to prevent complications associated with extensive skull-base drilling. None of our patients experienced postoperative hearing loss or CSF leakage. Furthermore, by avoiding dissection of the tentorium, we preserved the superior petrous sinus and did not coagulate the petrous vein in any of the patients. Consequently, complications related to vein coagulation were avoided. [45]\u003c/p\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eOur study demonstrates that the EA-PEA or EA-LSRA can be sufficient to achieve gross total resection of complex trigeminal schwannomas and enables surgery through Meckel's cave for tumors that have expanded into the middle and posterior fossae as well as those with extracranial extensions. The proposed classification system is helpful for determining the most appropriate approach to the lesion. Additionally, endoscope assistance helps avoid the extensive skull-base approach and complications related to a skull-base osteotomy and tentorial dissection. Using the endoscope after microsurgical resection helps to detect and resect residual tumor in blind spots and increases the total resection rate.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eACKNOWLEGMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;The authors thank Julie Yamamoto and Daniel Yamamoto for editing the text and G\u0026ouml;khan Canaz for artistic illustrations (Figures 1 and 2).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eCONFLICT OF INTEREST STATEMENT\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no personal, financial, or institutional interest in this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAUTHOR CONTRIBUTIONS\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Berk Burak Berker, Abuzer Gungor, Y\u0026uuml;cel Doğruel and Serdar Rahmanov. The first draft of the manuscript was written by Berk Burak Berker, Abuzer G\u0026uuml;ng\u0026ouml;r, Y\u0026uuml;cel Doğruel, Uğur T\u0026uuml;re and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis retrospective study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Yeditepe University review boards approved this study. Written informed consent was obtained from all individual participants included in the study and all enrolled patients or their families before conducting this clinical study. We followed the principle of confidentiality and respected any wishes of the patients.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding or financial support during the preparation of this study.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMcCormick PC, Bello JA, Post KD. Trigeminal schwannoma. Surgical series of 14 cases with review of the literature. \u003cem\u003eJ Neurosurg\u003c/em\u003e 1988; 69: 850\u0026ndash;860.\u003c/li\u003e\n\u003cli\u003eJEFFERSON G. The trigeminal neurinomas with some remarks on malignant invasion of the gasserian ganglion. \u003cem\u003eClin Neurosurg\u003c/em\u003e 1953; 1: 11\u0026ndash;54.\u003c/li\u003e\n\u003cli\u003eLesoin F, Rousseaux M, Villette L, et al. 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Neurinomas of the trigeminal nerve. \u003cem\u003eAm J Otolaryngol\u003c/em\u003e 1984; 5: 301\u0026ndash;333.\u003c/li\u003e\n\u003cli\u003eKRAYENB\u0026Uuml;HL H. PRIMARY TUMOURS OF THE ROOT OF THE FIFTH CRANIAL NERVE: THEIR DISTINCTION FROM TUMOURS OF THE GASSERIAN GANGLION1. \u003cem\u003eBrain\u003c/em\u003e 1936; 59: 337\u0026ndash;352.\u003c/li\u003e\n\u003cli\u003eWanibuchi M, Fukushima T, Zomordi AR, et al. Trigeminal schwannomas: skull base approaches and operative results in 105 patients. \u003cem\u003eNeurosurgery\u003c/em\u003e 2012; 70: 132\u0026ndash;144.\u003c/li\u003e\n\u003cli\u003eKonovalov AN, Spallone A, Mukhamedjanov DJ, et al. Trigeminal neurinomas. A series of 111 surgical cases from a single institution. \u003cem\u003eActa Neurochir (Wien)\u003c/em\u003e 1996; 138: 1027\u0026ndash;1035.\u003c/li\u003e\n\u003cli\u003eRhoton AL, Pulec JL, Hall GM, et al. Absence of bone over the geniculate ganglion. \u003cem\u003eJ Neurosurg\u003c/em\u003e 1968; 28: 48\u0026ndash;53.\u003c/li\u003e\n\u003cli\u003eKassam AB, Prevedello DM, Carrau RL, et al. The front door to Meckel\u0026rsquo;s cave: An anteromedial corridor via expanded endoscopic endonasal approach-technical considerations and clinical series. \u003cem\u003eNeurosurgery\u003c/em\u003e 2009; 64: 71\u0026ndash;83.\u003c/li\u003e\n\u003cli\u003eRaza SM, Donaldson AM, Mehta A, et al. Surgical management of trigeminal schwannomas: Defining the role for endoscopic endonasal approaches. \u003cem\u003eNeurosurg Focus\u003c/em\u003e 2014; 37: 1\u0026ndash;9.\u003c/li\u003e\n\u003cli\u003eAgosti E, Alexander AY, Choby G, et al. Combined endoscopic endonasal transpterygoid and sublabial transmaxillary approaches for a large infratemporal fossa trigeminal schwannoma. \u003cem\u003eActa Neurochir (Wien)\u003c/em\u003e 2022; 164: 2525\u0026ndash;2531.\u003c/li\u003e\n\u003cli\u003eShin SS, Gardner PA, Stefko ST, et al. Endoscopic endonasal approach for nonvestibular schwannomas. \u003cem\u003eNeurosurgery\u003c/em\u003e 2011; 69: 1046\u0026ndash;1057.\u003c/li\u003e\n\u003cli\u003eYang L, Hu L, Zhao W, et al. Endoscopic endonasal approach for trigeminal schwannomas: our experience of 39 patients in 10 years. \u003cem\u003eEur Arch Oto-Rhino-Laryngology\u003c/em\u003e 2018; 275: 735\u0026ndash;741.\u003c/li\u003e\n\u003cli\u003eWu X, Xie SH, Tang B, et al. Single-stage endoscopic endonasal approach for the complete removal of trigeminal schwannomas occupying both the middle and posterior fossae. \u003cem\u003eNeurosurg Rev\u003c/em\u003e 2021; 44: 607\u0026ndash;616.\u003c/li\u003e\n\u003cli\u003eBloch DC, Oghalai JS, Jackler RK, et al. The fate of the tumor remnant after less-than-complete acoustic neuroma resection. \u003cem\u003eOtolaryngol neck Surg Off J Am Acad Otolaryngol Neck Surg\u003c/em\u003e 2004; 130: 104\u0026ndash;112.\u003c/li\u003e\n\u003cli\u003eHasegawa T, Kida Y, Yoshimoto M, et al. Trigeminal schwannomas: results of gamma knife surgery in 37 cases. \u003cem\u003eJ Neurosurg\u003c/em\u003e 2007; 106: 18\u0026ndash;23.\u003c/li\u003e\n\u003cli\u003ePhi JH, Paek SH, Chung H-T, et al. Gamma Knife surgery and trigeminal schwannoma: is it possible to preserve cranial nerve function? \u003cem\u003eJ Neurosurg\u003c/em\u003e 2007; 107: 727\u0026ndash;732.\u003c/li\u003e\n\u003cli\u003eSheehan J, Yen CP, Arkha Y, et al. Gamma knife surgery for trigeminal schwannoma. \u003cem\u003eJ Neurosurg\u003c/em\u003e 2007; 106: 839\u0026ndash;845.\u003c/li\u003e\n\u003cli\u003eMalhotra A, Tu L, Kalra VB, et al. Neuroimaging of Meckel\u0026rsquo;s cave in normal and disease conditions. \u003cem\u003eInsights Imaging\u003c/em\u003e 2018; 9: 499\u0026ndash;510.\u003c/li\u003e\n\u003cli\u003eKoerbel A, Gharabaghi A, Safavi-Abbasi S, et al. Venous complications following petrosal vein sectioning in surgery of petrous apex meningiomas. \u003cem\u003eEur J Surg Oncol\u003c/em\u003e 2009; 35: 773\u0026ndash;779.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"endoscope assistance, skull base, trigeminal schwannoma","lastPublishedDoi":"10.21203/rs.3.rs-5211321/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5211321/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eOBJECTIVE\u003c/h2\u003e \u003cp\u003eThe objective of this study was to demonstrate that trigeminal schwannomas located in different cranial fossae can be resected entirely through Meckel\u0026rsquo;s cave without extensive skull-base drilling by taking either an endoscope-assisted pterional epidural approach (EA-PEA) or an endoscope-assisted lateral suboccipital retrosigmoid approach (EA-LSRA). Additionally, we describe a modified classification based on Jefferson\u0026rsquo;s system to determine the surgical approach.\u003c/p\u003e\u003ch2\u003eMETHODS\u003c/h2\u003e \u003cp\u003eThis is a retrospective study of 19 patients with trigeminal schwannomas in different cranial fossae who underwent EA-PEA or EA-LSRA .According to the proposed system, lesions in the middle fossa are classified as type A, those in the posterior fossa are type B, and lesions in both fossae are type C, the same as in Jefferson\u0026rsquo;s classification. Our modifications begin by classifying lesions extending into different fossae. Those located primarily in the middle cranial fossa are denoted type C1, whereas one predominantly occupying the posterior cranial fossa is type C2. Lesions with extracranial extensions are classified as type D. Patients with type A, type C1, and type D lesions underwent EA-PEA, while those with type B and C2 lesions were treated through EA-LSRA.\u003c/p\u003e\u003ch2\u003eRESULTS\u003c/h2\u003e \u003cp\u003eThirteen patients (68.4%) underwent EA-PEA and 6 (31.6%) underwent EA-LSRA. Gross total resection was accomplished in 16 patients (84.2%). No surgery-related complications were observed.\u003c/p\u003e\u003ch2\u003eCONCLUSION\u003c/h2\u003e \u003cp\u003eOur study demonstrates that EA-PEA and EA-LSRA can lead to gross total resection in patients with complex trigeminal schwannomas. Endoscope assistance helps avoid the extensive skull-base approaches. The proposed classification system is a guide for determining the surgical approach.\u003c/p\u003e","manuscriptTitle":"Endoscope-assisted trigeminal schwannoma resection without extensive skull-base drilling ","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-01 16:53:15","doi":"10.21203/rs.3.rs-5211321/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e0d46ba6-1018-4709-87a3-026abf9d7de9","owner":[],"postedDate":"December 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-01-23T12:38:48+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-01 16:53:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5211321","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5211321","identity":"rs-5211321","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}