Fully Endoscopic Retrosigmoid Approach For Pontine Metastasis As An Initial Presentation Of Lung Cancer: Surgical Anatomy And A Technical Case Report

Fully Endoscopic Retrosigmoid Approach For Pontine Metastasis As An Initial Presentation Of Lung Cancer: Surgical Anatomy And A Technical Case Report | 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 Case Report Fully Endoscopic Retrosigmoid Approach For Pontine Metastasis As An Initial Presentation Of Lung Cancer: Surgical Anatomy And A Technical Case Report Murat Kutlay, Sait Kayhan, Mehmet Can Ezgü, Can Korkmaz, Ayşegül Usve Türkcan, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7757694/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 The standard microsurgical retrosigmoid approach (mRSA) is one of the most commonly used techniques to access pontine lesions, and in recent years it has been enriched with the introduction of endoscopic methods. Although endoscopic retrosigmoid approaches (eRSAs) have been increasingly applied to various posterior fossa lesions, surgical treatment of a pontine metastasis using this technique has not been previously reported. We present the case of a previously healthy 72-year-old man who developed progressive right hemiparesis and gait disturbance. Magnetic resonance imaging revealed a cystic mass in the left side of the pons. Due to worsening symptoms, the patient underwent a fully endoscopic retrosigmoid approach with intraoperative neurophysiological monitoring, utilizing the peritrigeminal safe entry zone. Postoperatively, neurological function improved, and histopathological examination confirmed metastatic small cell carcinoma. To our knowledge, this is the first report of successful utilization of a fully endoscopic retrosigmoid approach in the management of a metastatic pontine tumor, emphasizing the surgical anatomy, technical nuances, and the importance of further case collections and collaborative studies to clarify the role of this minimally invasive approach. Neuroendoscopy Brainstem Pontine metastasis Retrosigmoid endoscopic approach Figures Figure 1 Figure 2 Figure 3 Introduction Brainstem metastases are uncommon, representing only 3–7% of all intracranial secondary tumors. 1 , 2 Within the brainstem, the pons is most frequently involved, followed by the midbrain and medulla. 3 , 4 Despite their relative rarity, these lesions carry a poor prognosis, with survival typically ranging between 4 and 12 months, and decreasing to approximately one month if left untreated. 2 , 5 , 6 , 7 The management of metastatic tumors in this eloquent region remains highly complex because of the dense concentration of critical neuroanatomical structures and the substantial risks associated with surgery. With the recent development of minimally invasive methods, the endoscopic endonasal transsphenoidal transclival (EETT) route has been introduced as a possible alternative for ventrally located pontine lesions. 1 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 Traditionally, the microscopic retrosigmoid approach (mRSA) has served as a standard technique for gaining access to a broad spectrum of posterior fossa pathologies. More recently, the incorporation of endoscopy has given rise to the endoscopic retrosigmoid approach (eRSA), which may be performed independently or in combination with microsurgery. This evolution has widened its application to various neoplastic and vascular conditions of the posterior fossa. 16 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 Nevertheless, reports describing the use of eRSA specifically for pontine tumors are exceedingly rare, with only two cavernoma cases published so far. Here, we describe a patient who presented with pontine metastasis as the first manifestation of lung cancer. To the best of our knowledge, this is the first report of a metastatic pontine lesion successfully treated with a fully endoscopic retrosigmoid approach. Case Presentation This previously healthy 72- year-old man was admitted to hospital for a gradual onset of right-sided hemiparesis (motor strength of 4/5 on the right), and gait disturbance which had arisen three days previously. Cranial CT with contrast and CT angiography demonstrated a cystic pontine lesion (Fig. 1 A-C). Contrast-enhanced MRI revealed a rim-enhancing cystic mass in the left side of the pons. Infectious laboratory tests of both serum and cerebrospinal fluid (CSF) revealed no evidence of inflammation or infection. Contrast-enhanced chest CT showed a right hilar mass lesion. Abdomen, and pelvis CT demonstrated no evidence of disease. On day 4 of admission, the patient’s condition exacerbated with headache, dizziness, and worsening hemiparesis. Physical examination revealed 3/5 strength on the right upper and 2/5 on the right lower extremity and hypoesthesia in the left half of the face. Given the progressive worsening of neurologic symptoms, the possibility of biopsy plus surgical decompression was offered to the patient. An honest discussion with the patient regarding the different treatment options, potential for postoperative worsening, and the surgery’s goals was performed. Multiple surgical approaches were discussed. After obtaining informed consent, the patient underwent a left-sided eRSA. Written informed consent was also obtained from the patient for publication of this case report and accompanying images. The study was conducted in accordance with the principles of the Declaration of Helsinki. Surgery Surgery was performed using 0 0 and 30 0 endoscopes (4-mm diameter, 18-cm length [Karl Storz SE & Co. KG, Tuttlingen, Germany]). Neurophysiologic monitoring, including somatosensory evoked potentials and motor evoked potentials, as well as monitoring of CNs V-VII-XII and lower cranial nerves was employed. We did not use an endoscope holder; instead, a 2-surgeon 3-hand technique was used where the assistant held the endoscope and the surgeon used both hands for bimanual manipulation. Intraoperative navigation with CT and MRI was used throughout the procedure. The patient was positioned in the lateral park bench position. The head was fixed with a three-point head holder and kept flexed and parallel to the floor. After a lazy S skin incision measuring approximately 5 cm in length, a left suboccipital craniectomy (~ 3x3 cm) was performed, exposing the edges of the transverse and sigmoid sinuses. The baseline MEP stimulation threshold was determined prior to opening the dura, and stimulation was intermittently performed throughout the surgery. Dura was opened in a cruciate fashion. The assistant placed the 00 endoscope in the surgical field. After gentle retraction of the cerebellum superomedially, the cerebellomedullary cistern was opened to facilitate drainage of CSF. A soaked cottonoid was advanced along the suboccipital surface of the cerebellum to reduce the risk of damaging the cerebellum by insertion and extraction of the endoscope and instruments. The endoscope was then progressively advanced between the cerebellar surface and the petrosal bone. After retraction of the cerebellum medially and dissection of the arachnoid, the first surgical landmark visualized was the 7th and 8th nerve complex. The anterior inferior cerebellar artery(AICA) was also identified (Fig. 3 A). Subsequently, the petrous surface of the cerebellum was carefully separated at its upper end, seeking to identify the junction between the tentorium and the posterior superior aspect of the petrous temporal bone, in order to locate the superior petrous sinus, the superior petrous vein and the 5th nerve (Fig. 3 B, 3 C). No color change or other abnormality was observed on the pons surface. The ‘peritrigeminal safe entry zone’ between the trigeminal and facial nerves was identified (Fig. 3 D). After a gentle bipolar coagulation (Fig. 3 E), a 5-mm longitudinal incision was made under the guidance of the neuronavigation and also confirming a lack of MEP response (Fig. 3 F) Forceps opening was used to stretch and displace the fibers to allow drainage of the cystic component of the tumor (Fig. 3 G). Cyst contents comprised xanthochromic like fluid (Fig. 3 H, 3 I). The remains were gently removed from the walls of the lesion as much as possible using a teardrop suction, angled blunt curette and micropituitary forceps under 30 0 endoscopic visualization. Intraoperative frozen section suggested metastasis. After hemostasis was achieved, the dura was closed watertight by 4–0 prolene. The muscles were closed in two layers. Superficial wound closure was performed in the usual fashion. Postoperative Course The patient was extubated after the operation and admitted in the neurosurgical intensive care unit for neurologic monitoring for 24 h. No major complication was showed on the early postoperative CT scan. The postoperative course was uneventful. The hemiparesis remained unchanged in the immediate postoperative period. On postoperative day 3, his hemiparesis had improved to 4/5 strength and he could walk on postoperative day 5. MRI performed on the 2nd day after surgery demonstrated that the surgical cavity filled with mixed density blood products. The pathological diagnosis metastatic small cell cancer (SCc). On postoperative day 10, we referred him to oncology department for further evaluation and treatment Discussion Small cell carcinoma (SCC) represents approximately 20% of all lung cancers. At the time of diagnosis, nearly 10% of patients already have intracranial dissemination, with the pons being the most frequent brainstem site. Metastatic lesions in this eloquent region create significant therapeutic challenges because of their deep location and the critical neuroanatomy involved. Standard treatment strategies are often associated with poor outcomes. 34,35 Stereotactic radiosurgery (SRS) has emerged as a noninvasive treatment option and, although survival rates appear encouraging, it carries notable risks. In brainstem metastases, severe complications such as radiation necrosis resistant to corticosteroids and intralesional hemorrhage have been described, with rates approaching 9.5%. Local disease progression within the brainstem is frequently accompanied by sudden neurological deterioration or even death. In carefully selected patients, particularly in those with cystic lesions and rapidly worsening deficits, surgical intervention may therefore provide a life-saving benefit, as illustrated in our case. Surgery for brainstem metastases is technically formidable because of the densely packed, highly eloquent tissue surrounding these lesions. 4 , 5 , 6 , 7 , 36 Nevertheless, improvements in imaging modalities, neuronavigation, and intraoperative neurophysiological monitoring have expanded the safety margin of microsurgical approaches. Although neuronavigation assists in determining the optimal entry point, intraoperative brain shift may limit its accuracy, underscoring the importance of neurophysiological monitoring and functional mapping. Diffusion tensor imaging (DTI) tractography further contributes to preoperative planning, and its integration with conventional MRI enables more precise definition of the safest surgical corridors. 13 , 18 , 20 , 25 , 36 , 37 In recent years, the traditional microsurgical retrosigmoid approach (mRSA) has been supplemented by endoscopic techniques, broadening its applicability to posterior fossa lesions. 16 , 28 , 29 , 38 , 39 Endoscopic assistance within the retrosigmoid corridor has been described across a wide spectrum of pathologies, functioning either as the primary operative method or as an adjunct to microsurgery. Reported indications include vestibular schwannomas, epidermoid and arachnoid cysts, meningiomas, neurovascular compression syndromes such as trigeminal neuralgia and hemifacial spasm, as well as intracranial aneurysms. 21 , 23 , 24 , 26 , 27 , 30 , 31 , 32 , 33 , 40 , 41 , 42 , 43 , 44 , 45 Despite these advances, purely endoscopic retrosigmoid approaches (eRSA) applied to pontine lesions remain exceedingly rare. To date, only two cases have been documented in the literature, both involving cavernomas. Nayak et al. described the resection of a pontine cavernoma through eRSA, whereas Sandalcioglu et al. reported a microsurgical resection followed by endoscopic inspection to verify the extent of removal, though the endoscope itself was not directly employed for excision. 16 , 46 To our knowledge, the present case constitutes the first report of a pontine metastasis successfully treated by means of a fully endoscopic retrosigmoid approach. When planning surgery for brainstem lesions, the “two-point method” is frequently applied, in which a hypothetical line from the lesion’s center to the nearest pial surface defines the least disruptive route of access. 8 , 16 , 36 , 47 In cases where the lesion does not reach the surface, anatomical “safe entry zones” can be exploited to minimize injury to critical neural pathways. 8,9,25,36,41,48,49,50 Among these, the peritrigeminal safe entry zone (PTSEZ) is often considered the most reliable entry point for pontine surgery. Located between the trigeminal and facial nerves, it is situated lateral to the corticospinal tract and anterior to the trigeminal sensory and motor nuclei. When this zone is selected, care must be taken to preserve intrapontine fibers of cranial nerves VI, VII, and VIII, which course in an anteroposterior direction. 5 , 20 , 25 , 36 , 37 , 48 , 51 Debate continues regarding whether the incision through the PTSEZ should be longitudinal or transverse. A longitudinal incision is commonly preferred between the trigeminal and facial nerves, while a transverse cut may theoretically parallel pontine fiber orientation and limit disruption. However, each carries distinct risks: a longitudinal incision can encounter the corticospinal tract at greater depth, whereas a transverse incision may jeopardize the trigeminal motor and sensory nuclei, the spinal trigeminal tract, and the intrapontine segment of the facial nerve. 25 , 36 , 50 , 51 , 52 Accordingly, meticulous preoperative planning and intraoperative monitoring are indispensable. The role of dynamic versus fixed endoscopy also remains controversial. Critics of the dynamic technique argue that repeated entry and withdrawal of the endoscope heightens the chance of neurovascular injury. Conversely, many surgeons highlight its advantages in terms of flexibility and visualization. In our case, a freehand dynamic technique was employed. We believe that the fixed technique poses inherent drawbacks, including the creation of a blind corridor behind the endoscope lens, which may conceal structures during instrument manipulation. Furthermore, prolonged procedures risk thermal injury to cranial nerves VII and VIII due to heat emission from the endoscope tip. 10 , 16 , 22 , 23 , 29 , 31 , 33 , 53 Conclusion We report the first case of a pontine metastasis successfully treated with a fully endoscopic retrosigmoid approach. This experience illustrates the feasibility and potential safety of the technique when applied to carefully selected patients and supported by a surgical team proficient in endoscopic procedures. Patient selection and the availability of an experienced assistant are critical determinants of outcome. We consider that further accumulation of similar case reports, along with multicenter collaborative investigations, will be essential to better define the role and long-term significance of this approach in the management of pontine tumors. Declarations Conflicts of Interest Disclosure The authors declare that they have no conflicts of interest related to this manuscript. Ethics Statement This study was approved by the Ethics Committee for Non-interventional Scientific Research of Gulhane Training and Research Hospital (Date: June 12, 2025; No: 2025/112). Written informed consent was obtained from the patient for publication of this case report and accompanying images. The study was conducted in accordance with the principles of the Declaration of Helsinki. Author Contribution Author Contributions StatementM.K. conceived and designed the study, supervised surgical planning, and drafted the manuscript. S.K. performed the surgery and assisted in manuscript preparation. 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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-7757694","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":536473882,"identity":"73258817-6004-4bc0-a494-71e9cf066374","order_by":0,"name":"Murat Kutlay","email":"","orcid":"","institution":"Sağlık Bilimleri Üniversitesi","correspondingAuthor":false,"prefix":"","firstName":"Murat","middleName":"","lastName":"Kutlay","suffix":""},{"id":536473883,"identity":"9b01619a-ad5b-4f70-929d-602175b3a8ca","order_by":1,"name":"Sait Kayhan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+0lEQVRIiWNgGAWjYDCCAyDCAAgZeICMCgkGPiAlQYQWA6iWMxIMbMRpYYBqYWxjIKyF7/YB5g8/Cv4Y88/IPfi5cJ6FPBt7j+ENhhqbaFxaJM8lsEn2GBiYSdzIS5aeuU3CsI3njLEFw7G03AYcWgzOAF3CY2Bgw3Ajx0Cad5tEAptEjpkEY8NhfFqYP/4BapG/kWP8m3cOcVoYpIG2mBncyDGT5m0gQovkGcY2aRkDY2PDM2/MrHmOgfxyrNgiAY9f+M4wH/745o+c4bzjOca3eWrq5PnZmzfe+FBjg1MLMC6gUgIJSIIJmOqwAP4DRCkbBaNgFIyCEQgASdpPH+npkcEAAAAASUVORK5CYII=","orcid":"","institution":"Sağlık Bilimleri Üniversitesi","correspondingAuthor":true,"prefix":"","firstName":"Sait","middleName":"","lastName":"Kayhan","suffix":""},{"id":536473884,"identity":"a3373e8b-7112-4b87-b77b-0c3c080b7b74","order_by":2,"name":"Mehmet Can Ezgü","email":"","orcid":"","institution":"Sağlık Bilimleri Üniversitesi","correspondingAuthor":false,"prefix":"","firstName":"Mehmet","middleName":"Can","lastName":"Ezgü","suffix":""},{"id":536473885,"identity":"3526fa4d-2599-41bc-a977-117389a2caa5","order_by":3,"name":"Can Korkmaz","email":"","orcid":"","institution":"Sağlık Bilimleri Üniversitesi","correspondingAuthor":false,"prefix":"","firstName":"Can","middleName":"","lastName":"Korkmaz","suffix":""},{"id":536473886,"identity":"62d6f664-1779-415e-81ca-a3dafb91f8ec","order_by":4,"name":"Ayşegül Usve Türkcan","email":"","orcid":"","institution":"Sağlık Bilimleri Üniversitesi","correspondingAuthor":false,"prefix":"","firstName":"Ayşegül","middleName":"Usve","lastName":"Türkcan","suffix":""},{"id":536473887,"identity":"126c91de-4e23-4134-9209-329a2e9682e8","order_by":5,"name":"Yusuf İzci","email":"","orcid":"","institution":"Sağlık Bilimleri Üniversitesi","correspondingAuthor":false,"prefix":"","firstName":"Yusuf","middleName":"","lastName":"İzci","suffix":""}],"badges":[],"createdAt":"2025-10-01 08:23:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7757694/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7757694/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":94728656,"identity":"d3fda402-1c8c-4515-b3a9-44795c19822d","added_by":"auto","created_at":"2025-10-30 07:04:08","extension":"tiff","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1569844,"visible":true,"origin":"","legend":"","description":"","filename":"Figure1..tiff","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/305aedddebf7d7254a39138c.tiff"},{"id":94727959,"identity":"a39325eb-7c56-4f71-8873-8c6a2c8bde20","added_by":"auto","created_at":"2025-10-30 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07:03:36","extension":"tiff","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3694494,"visible":true,"origin":"","legend":"","description":"","filename":"Figure2..tiff","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/1d8654a3fe3a5c06995687fb.tiff"},{"id":94728288,"identity":"e09d7299-57e1-4283-a095-d801749c0ac4","added_by":"auto","created_at":"2025-10-30 07:03:28","extension":"tiff","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1777566,"visible":true,"origin":"","legend":"","description":"","filename":"Figure3..tiff","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/802929c055b9f08d671d7b3c.tiff"},{"id":94681061,"identity":"4d401a31-f7e5-4689-a934-5e2acada27fa","added_by":"auto","created_at":"2025-10-29 14:50:41","extension":"png","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":88093,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigure1..png","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/3b4b0f0c3f5a0942031a58e9.png"},{"id":94681067,"identity":"f4e9cfd1-2a4c-468b-831b-e942decacbb0","added_by":"auto","created_at":"2025-10-29 14:50:41","extension":"png","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":799300,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigure2..png","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/4cd3485ff65d15229ce24a6f.png"},{"id":94681072,"identity":"498cf447-7895-43db-892b-9090eb98f7ad","added_by":"auto","created_at":"2025-10-29 14:50:41","extension":"png","order_by":11,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":131599,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigure3..png","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/82683be9f06e096dbac5edcb.png"},{"id":94728294,"identity":"6e3dc122-54f9-47cd-a267-772f1148b209","added_by":"auto","created_at":"2025-10-30 07:03:28","extension":"xml","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":102001,"visible":true,"origin":"","legend":"","description":"","filename":"06ee3b02399542559c3bd1adb2e2bca51structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/df28a69d60cfbd6bdf7dcfac.xml"},{"id":94681073,"identity":"93083ed9-ddea-4c59-b163-9addb371c4dc","added_by":"auto","created_at":"2025-10-29 14:50:41","extension":"html","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":110856,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/06c3f91eb847e818f12c6376.html"},{"id":94681059,"identity":"b2b5f871-479c-48dc-8ab1-02e901190ffb","added_by":"auto","created_at":"2025-10-29 14:50:41","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1583254,"visible":true,"origin":"","legend":"\u003cp\u003ePreoperative axial CT scan with contrast \u003cstrong\u003e(A)\u003c/strong\u003e, sagittal angiogram \u003cstrong\u003e(B)\u003c/strong\u003e, and coronal \u003cstrong\u003e(C)\u003c/strong\u003e CT angiogram demonstrating left-sided intraaxial hypodense pontine lesion (red star).\u003c/p\u003e","description":"","filename":"Figure1..png","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/1e1c1fe57347506d3bb50db4.png"},{"id":94681060,"identity":"b91686fd-36ec-46c6-8c07-f047913f0922","added_by":"auto","created_at":"2025-10-29 14:50:41","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2575025,"visible":true,"origin":"","legend":"\u003cp\u003ePreoperative contrast- enhanced axial T1-weighted \u003cstrong\u003e(A)\u003c/strong\u003e, axial T2-weighted \u003cstrong\u003e(B)\u003c/strong\u003e, sagittal T1-weighted \u003cstrong\u003e(C)\u003c/strong\u003e, and coronal T2 weighted \u003cstrong\u003e(D)\u003c/strong\u003e, MR images showing a cystic lesion located in the left side of the pons. Postoperative day 2 contrast- enhanced axial T2-weighted \u003cstrong\u003e(E,F)\u003c/strong\u003e, sagittal T1-weighted \u003cstrong\u003e(G)\u003c/strong\u003e, and coronal T2-weighted MR images showing surgical cavity filled with mixed density blood products. There are some enhancement around the surgical cavity, which most likely represented postsurgical changes.\u003c/p\u003e","description":"","filename":"Figure2..png","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/809001a5d46dbf987321c02e.png"},{"id":94727951,"identity":"2c412be5-06a5-47a1-a7e9-6931ab6740ca","added_by":"auto","created_at":"2025-10-30 07:02:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":5064282,"visible":true,"origin":"","legend":"\u003cp\u003eIntraoperative endoscopic images captured during surgery. \u003cstrong\u003e(A)\u003c/strong\u003e, the left 7th and 8th complex (red star) at the entrance to the internal auditory canal (blue star),and the AICA (white arrow). \u003cstrong\u003e(B)\u003c/strong\u003e, after completion of the arachnoid dissection, view of the superior petrous sinus (black star) , the superior petrous vein complex (yellow star), the left 7th and 8th complex (red star) and the course of AICA (white arrows). \u003cstrong\u003e(C)\u003c/strong\u003e, expojur of the left 5th nerve (green star). The anterolateral surface of the pons is also visible in this endoscopic view (gray star). \u003cstrong\u003e(D)\u003c/strong\u003e, identification of the peritrigeminel safe entry zone, and a gentle bipolar coagulation of a small area in this zone. €, view of after coagulation (yellow arrow). \u003cstrong\u003e(F)\u003c/strong\u003e, performing the longitudinal incision (white arrow). \u003cstrong\u003e(G and H)\u003c/strong\u003e, forceps (f) opening was used to stretch and displace the fibers to allow drainage of the cystic component of the tumor. I, closing - up to the site of incision. Cyst contents comprised xanthochromic like fluid (gray arrow).\u003c/p\u003e\n\u003cp\u003eCP = cotton piece, S= suction, bf = bipolar forceps\u003c/p\u003e","description":"","filename":"Figure3..png","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/ccc0355140cfda8edc9ac873.png"},{"id":94731122,"identity":"c983bc49-6038-4010-bd8d-9009b3fd6264","added_by":"auto","created_at":"2025-10-30 07:07:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":10927276,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7757694/v1/2e61350c-52b9-4f1e-976f-ae5a9275609b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Fully Endoscopic Retrosigmoid Approach For Pontine Metastasis As An Initial Presentation Of Lung Cancer: Surgical Anatomy And A Technical Case Report","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBrainstem metastases are uncommon, representing only 3\u0026ndash;7% of all intracranial secondary tumors.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e Within the brainstem, the pons is most frequently involved, followed by the midbrain and medulla.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Despite their relative rarity, these lesions carry a poor prognosis, with survival typically ranging between 4 and 12 months, and decreasing to approximately one month if left untreated.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eThe management of metastatic tumors in this eloquent region remains highly complex because of the dense concentration of critical neuroanatomical structures and the substantial risks associated with surgery. With the recent development of minimally invasive methods, the endoscopic endonasal transsphenoidal transclival (EETT) route has been introduced as a possible alternative for ventrally located pontine lesions.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eTraditionally, the microscopic retrosigmoid approach (mRSA) has served as a standard technique for gaining access to a broad spectrum of posterior fossa pathologies. More recently, the incorporation of endoscopy has given rise to the endoscopic retrosigmoid approach (eRSA), which may be performed independently or in combination with microsurgery. This evolution has widened its application to various neoplastic and vascular conditions of the posterior fossa.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e Nevertheless, reports describing the use of eRSA specifically for pontine tumors are exceedingly rare, with only two cavernoma cases published so far.\u003c/p\u003e\u003cp\u003eHere, we describe a patient who presented with pontine metastasis as the first manifestation of lung cancer. To the best of our knowledge, this is the first report of a metastatic pontine lesion successfully treated with a fully endoscopic retrosigmoid approach.\u003c/p\u003e"},{"header":"Case Presentation","content":"\u003cp\u003eThis previously healthy 72- year-old man was admitted to hospital for a gradual onset of right-sided hemiparesis (motor strength of 4/5 on the right), and gait disturbance which had arisen three days previously. Cranial CT with contrast and CT angiography demonstrated a cystic pontine lesion (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-C). Contrast-enhanced MRI revealed a rim-enhancing cystic mass in the left side of the pons. Infectious laboratory tests of both serum and cerebrospinal fluid (CSF) revealed no evidence of inflammation or infection. Contrast-enhanced chest CT showed a right hilar mass lesion. Abdomen, and pelvis CT demonstrated no evidence of disease.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eOn day 4 of admission, the patient\u0026rsquo;s condition exacerbated with headache, dizziness, and worsening hemiparesis. Physical examination revealed 3/5 strength on the right upper and 2/5 on the right lower extremity and hypoesthesia in the left half of the face. Given the progressive worsening of neurologic symptoms, the possibility of biopsy plus surgical decompression was offered to the patient. An honest discussion with the patient regarding the different treatment options, potential for postoperative worsening, and the surgery\u0026rsquo;s goals was performed. Multiple surgical approaches were discussed. After obtaining informed consent, the patient underwent a left-sided eRSA. Written informed consent was also obtained from the patient for publication of this case report and accompanying images. The study was conducted in accordance with the principles of the Declaration of Helsinki.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eSurgery\u003c/h2\u003e\u003cp\u003eSurgery was performed using 0\u003csup\u003e0\u003c/sup\u003e and 30\u003csup\u003e0\u003c/sup\u003e endoscopes (4-mm diameter, 18-cm length [Karl Storz SE \u0026amp; Co. KG, Tuttlingen, Germany]). Neurophysiologic monitoring, including somatosensory evoked potentials and motor evoked potentials, as well as monitoring of CNs V-VII-XII and lower cranial nerves was employed. We did not use an endoscope holder; instead, a 2-surgeon 3-hand technique was used where the assistant held the endoscope and the surgeon used both hands for bimanual manipulation. Intraoperative navigation with CT and MRI was used throughout the procedure.\u003c/p\u003e\u003cp\u003eThe patient was positioned in the lateral park bench position. The head was fixed with a three-point head holder and kept flexed and parallel to the floor. After a lazy S skin incision measuring approximately 5 cm in length, a left suboccipital craniectomy (~\u0026thinsp;3x3 cm) was performed, exposing the edges of the transverse and sigmoid sinuses. The baseline MEP stimulation threshold was determined prior to opening the dura, and stimulation was intermittently performed throughout the surgery. Dura was opened in a cruciate fashion. The assistant placed the 00 endoscope in the surgical field. After gentle retraction of the cerebellum superomedially, the cerebellomedullary cistern was opened to facilitate drainage of CSF. A soaked cottonoid was advanced along the suboccipital surface of the cerebellum to reduce the risk of damaging the cerebellum by insertion and extraction of the endoscope and instruments. The endoscope was then progressively advanced between the cerebellar surface and the petrosal bone. After retraction of the cerebellum medially and dissection of the arachnoid, the first surgical landmark visualized was the 7th and 8th nerve complex. The anterior inferior cerebellar artery(AICA) was also identified (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Subsequently, the petrous surface of the cerebellum was carefully separated at its upper end, seeking to identify the junction between the tentorium and the posterior superior aspect of the petrous temporal bone, in order to locate the superior petrous sinus, the superior petrous vein and the 5th nerve (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). No color change or other abnormality was observed on the pons surface. The \u0026lsquo;peritrigeminal safe entry zone\u0026rsquo; between the trigeminal and facial nerves was identified (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD). After a gentle bipolar coagulation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE), a 5-mm longitudinal incision was made under the guidance of the neuronavigation and also confirming a lack of MEP response (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF) Forceps opening was used to stretch and displace the fibers to allow drainage of the cystic component of the tumor (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eG). Cyst contents comprised xanthochromic like fluid (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eH,\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eI). The remains were gently removed from the walls of the lesion as much as possible using a teardrop suction, angled blunt curette and micropituitary forceps under 30\u003csup\u003e0\u003c/sup\u003eendoscopic visualization. Intraoperative frozen section suggested metastasis. After hemostasis was achieved, the dura was closed watertight by 4\u0026ndash;0 prolene. The muscles were closed in two layers. Superficial wound closure was performed in the usual fashion.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003ePostoperative Course\u003c/h3\u003e\n\u003cp\u003eThe patient was extubated after the operation and admitted in the neurosurgical intensive care unit for neurologic monitoring for 24 h. No major complication was showed on the early postoperative CT scan. The postoperative course was uneventful. The hemiparesis remained unchanged in the immediate postoperative period. On postoperative day 3, his hemiparesis had improved to 4/5 strength and he could walk on postoperative day 5. MRI performed on the 2nd day after surgery demonstrated that the surgical cavity filled with mixed density blood products. The pathological diagnosis metastatic small cell cancer (SCc). On postoperative day 10, we referred him to oncology department for further evaluation and treatment\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eSmall cell carcinoma (SCC) represents approximately 20% of all lung cancers. At the time of diagnosis, nearly 10% of patients already have intracranial dissemination, with the pons being the most frequent brainstem site. Metastatic lesions in this eloquent region create significant therapeutic challenges because of their deep location and the critical neuroanatomy involved. Standard treatment strategies are often associated with poor outcomes. \u003csup\u003e34,35\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eStereotactic radiosurgery (SRS) has emerged as a noninvasive treatment option and, although survival rates appear encouraging, it carries notable risks. In brainstem metastases, severe complications such as radiation necrosis resistant to corticosteroids and intralesional hemorrhage have been described, with rates approaching 9.5%. Local disease progression within the brainstem is frequently accompanied by sudden neurological deterioration or even death. In carefully selected patients, particularly in those with cystic lesions and rapidly worsening deficits, surgical intervention may therefore provide a life-saving benefit, as illustrated in our case.\u003c/p\u003e\u003cp\u003eSurgery for brainstem metastases is technically formidable because of the densely packed, highly eloquent tissue surrounding these lesions.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e Nevertheless, improvements in imaging modalities, neuronavigation, and intraoperative neurophysiological monitoring have expanded the safety margin of microsurgical approaches. Although neuronavigation assists in determining the optimal entry point, intraoperative brain shift may limit its accuracy, underscoring the importance of neurophysiological monitoring and functional mapping. Diffusion tensor imaging (DTI) tractography further contributes to preoperative planning, and its integration with conventional MRI enables more precise definition of the safest surgical corridors.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eIn recent years, the traditional microsurgical retrosigmoid approach (mRSA) has been supplemented by endoscopic techniques, broadening its applicability to posterior fossa lesions.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e Endoscopic assistance within the retrosigmoid corridor has been described across a wide spectrum of pathologies, functioning either as the primary operative method or as an adjunct to microsurgery. Reported indications include vestibular schwannomas, epidermoid and arachnoid cysts, meningiomas, neurovascular compression syndromes such as trigeminal neuralgia and hemifacial spasm, as well as intracranial aneurysms.\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e,\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e,\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eDespite these advances, purely endoscopic retrosigmoid approaches (eRSA) applied to pontine lesions remain exceedingly rare. To date, only two cases have been documented in the literature, both involving cavernomas. Nayak et al. described the resection of a pontine cavernoma through eRSA, whereas Sandalcioglu et al. reported a microsurgical resection followed by endoscopic inspection to verify the extent of removal, though the endoscope itself was not directly employed for excision.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e To our knowledge, the present case constitutes the first report of a pontine metastasis successfully treated by means of a fully endoscopic retrosigmoid approach.\u003c/p\u003e\u003cp\u003eWhen planning surgery for brainstem lesions, the \u0026ldquo;two-point method\u0026rdquo; is frequently applied, in which a hypothetical line from the lesion\u0026rsquo;s center to the nearest pial surface defines the least disruptive route of access.\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e In cases where the lesion does not reach the surface, anatomical \u0026ldquo;safe entry zones\u0026rdquo; can be exploited to minimize injury to critical neural pathways. \u003csup\u003e8,9,25,36,41,48,49,50\u003c/sup\u003e Among these, the peritrigeminal safe entry zone (PTSEZ) is often considered the most reliable entry point for pontine surgery. Located between the trigeminal and facial nerves, it is situated lateral to the corticospinal tract and anterior to the trigeminal sensory and motor nuclei. When this zone is selected, care must be taken to preserve intrapontine fibers of cranial nerves VI, VII, and VIII, which course in an anteroposterior direction.\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e,\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eDebate continues regarding whether the incision through the PTSEZ should be longitudinal or transverse. A longitudinal incision is commonly preferred between the trigeminal and facial nerves, while a transverse cut may theoretically parallel pontine fiber orientation and limit disruption. However, each carries distinct risks: a longitudinal incision can encounter the corticospinal tract at greater depth, whereas a transverse incision may jeopardize the trigeminal motor and sensory nuclei, the spinal trigeminal tract, and the intrapontine segment of the facial nerve.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e,\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e,\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e Accordingly, meticulous preoperative planning and intraoperative monitoring are indispensable.\u003c/p\u003e\u003cp\u003eThe role of dynamic versus fixed endoscopy also remains controversial. Critics of the dynamic technique argue that repeated entry and withdrawal of the endoscope heightens the chance of neurovascular injury. Conversely, many surgeons highlight its advantages in terms of flexibility and visualization. In our case, a freehand dynamic technique was employed. We believe that the fixed technique poses inherent drawbacks, including the creation of a blind corridor behind the endoscope lens, which may conceal structures during instrument manipulation. Furthermore, prolonged procedures risk thermal injury to cranial nerves VII and VIII due to heat emission from the endoscope tip.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eWe report the first case of a pontine metastasis successfully treated with a fully endoscopic retrosigmoid approach. This experience illustrates the feasibility and potential safety of the technique when applied to carefully selected patients and supported by a surgical team proficient in endoscopic procedures. Patient selection and the availability of an experienced assistant are critical determinants of outcome. We consider that further accumulation of similar case reports, along with multicenter collaborative investigations, will be essential to better define the role and long-term significance of this approach in the management of pontine tumors.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflicts of Interest Disclosure\u003c/h2\u003e\u003cp\u003eThe authors declare that they have no conflicts of interest related to this manuscript.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eEthics Statement\u003c/h2\u003e\u003cp\u003eThis study was approved by the Ethics Committee for Non-interventional Scientific Research of Gulhane Training and Research Hospital (Date: June 12, 2025; No: 2025/112). Written informed consent was obtained from the patient for publication of this case report and accompanying images. The study was conducted in accordance with the principles of the Declaration of Helsinki.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor Contributions StatementM.K. conceived and designed the study, supervised surgical planning, and drafted the manuscript. S.K. performed the surgery and assisted in manuscript preparation. A.U.T. contributed to the literature review and editing. M.C.E. and C.K. assisted with data collection and figures. Y.İ. critically reviewed the work and provided final supervision. All authors approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGerges MM, Godil SS, Kacker A, Schwartz TH. Endoscopic endonasal transclival resection of a pontine metastasis: case report and operative video. 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Laryngoscope. 2014;124:E332-9.\u003c/span\u003e\u003c/li\u003e\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":"Neuroendoscopy, Brainstem, Pontine metastasis, Retrosigmoid endoscopic approach","lastPublishedDoi":"10.21203/rs.3.rs-7757694/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7757694/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe standard microsurgical retrosigmoid approach (mRSA) is one of the most commonly used techniques to access pontine lesions, and in recent years it has been enriched with the introduction of endoscopic methods. Although endoscopic retrosigmoid approaches (eRSAs) have been increasingly applied to various posterior fossa lesions, surgical treatment of a pontine metastasis using this technique has not been previously reported. We present the case of a previously healthy 72-year-old man who developed progressive right hemiparesis and gait disturbance. Magnetic resonance imaging revealed a cystic mass in the left side of the pons. Due to worsening symptoms, the patient underwent a fully endoscopic retrosigmoid approach with intraoperative neurophysiological monitoring, utilizing the peritrigeminal safe entry zone. Postoperatively, neurological function improved, and histopathological examination confirmed metastatic small cell carcinoma. To our knowledge, this is the first report of successful utilization of a fully endoscopic retrosigmoid approach in the management of a metastatic pontine tumor, emphasizing the surgical anatomy, technical nuances, and the importance of further case collections and collaborative studies to clarify the role of this minimally invasive approach.\u003c/p\u003e","manuscriptTitle":"Fully Endoscopic Retrosigmoid Approach For Pontine Metastasis As An Initial Presentation Of Lung Cancer: Surgical Anatomy And A Technical Case Report","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-29 14:50:36","doi":"10.21203/rs.3.rs-7757694/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":"757936f1-ee3e-4cc0-ba4b-b2055c458476","owner":[],"postedDate":"October 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-12T09:10:23+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-29 14:50:36","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7757694","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7757694","identity":"rs-7757694","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}