Flow-related Intrameatal AICA Aneurysm Associated with a Cerebellar Pial AVF: Diagnostic Features and Multimodality Management

Flow-related Intrameatal AICA Aneurysm Associated with a Cerebellar Pial AVF: Diagnostic Features and Multimodality Management | 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 Flow-related Intrameatal AICA Aneurysm Associated with a Cerebellar Pial AVF: Diagnostic Features and Multimodality Management Hiroaki Matsumoto, Yasunori Yoshida, Akihiro Okada, Hiroaki Minami, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9110986/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 Intrameatal aneurysms of the anterior inferior cerebellar artery (AICA) are extremely rare, particularly when associated with distal arteriovenous shunts. We report a ruptured intrameatal AICA aneurysm associated with a cerebellar pial arteriovenous fistula (AVF) and describe its imaging characteristics and multimodality management. A 68-year-old woman presented with sudden onset of severe headache and vomiting. Computed tomography revealed subarachnoid hemorrhage predominantly in the posterior fossa. Digital subtraction angiography demonstrated a small intrameatal AICA aneurysm and a cerebellar arteriovenous shunt without an intervening nidus, consistent with a pial AVF supplied by the AICA, brainstem perforators, and the superior cerebellar artery. The aneurysm was considered a flow-related lesion caused by increased hemodynamic stress from the distal shunt. Parent artery occlusion of the AICA was performed to secure the aneurysm and reduce shunt flow, followed by Gamma Knife radiosurgery for the residual AVF. Follow-up angiography confirmed complete obliteration. anterior inferior cerebellar artery intrameatal aneurysm pial arteriovenous fistula flow-related aneurysm endovascular treatment Gamma Knife radiosurgery Figures Figure 1 Figure 2 Introduction Aneurysms arising from the anterior inferior cerebellar artery (AICA) are rare, representing less than 1% of all intracranial aneurysms [ 1 ]. Among these, aneurysms located within the internal auditory canal (intrameatal AICA aneurysms) are particularly uncommon, with only a few reported cases [ 1 – 7 ]. Flow-related aneurysms may arise in association with intracranial arteriovenous shunts, most often with arteriovenous malformations (AVMs) or dural arteriovenous fistulas (AVFs), whereas their occurrence in the AICA is rare [ 2 , 5 , 7 , 8 ]. Association with a distal pial AVF is especially uncommon. We report a case of a flow-related intrameatal AICA aneurysm associated with a cerebellar pial AVF that required a multimodality treatment strategy. Case description A 68-year-old woman presented with sudden onset of severe headache and vomiting. Computed tomography revealed subarachnoid hemorrhage (SAH) predominantly in the posterior fossa (Fig. 1 A). On admission, the patient had mild disturbance of consciousness without facial nerve palsy or hearing impairment, and her clinical grade was Hunt and Kosnik grade 2. Magnetic resonance angiography did not clearly demonstrate an aneurysm, but time‑of‑flight source images suggested a small lesion in the right internal auditory canal (Fig. 1 B). Digital subtraction angiography demonstrated an intrameatal AICA aneurysm with an associated cerebellar arteriovenous shunt (Fig. 1 C–G). No nidus was identified. Contrast‑enhanced magnetic resonance imaging showed a focal shunt point at the brainstem–cerebellar border rather than within the dura (Fig. 1 H, I), supporting the diagnosis of a cerebellar pial AVF. The lesion was supplied by three arterial feeders: the AICA, brainstem perforators, and the superior cerebellar artery (SCA) (Fig. 1 J). The aneurysm was considered a flow‑related lesion induced by hemodynamic stress from the distal shunt. Selective AICA angiography showed no significant supply to normal cerebellar or brainstem territories from the involved segment (Fig. 1 E, F). The aneurysm measured approximately 2.5 mm and lacked a clearly defined neck, making selective coil embolization technically difficult. Reduction of shunt flow from the pial AVF was deemed necessary. Although facial nerve palsy and hearing impairment were possible, the risk of cerebellar or brainstem infarction was considered low. Therefore, parent artery occlusion (PAO) of the AICA using coils was performed to secure the aneurysm and reduce shunt flow from the pial AVF (Fig. 2 A). The brainstem perforating feeder was then embolized with N‑butyl cyanoacrylate, but the SCA feeder could not be treated because catheter navigation was difficult. Because a residual shunt persisted at the 3-month follow-up after endovascular treatment, Gamma Knife radiosurgery was performed (Fig. 2 B–D). Follow-up imaging demonstrated complete obliteration of the AVF without recurrence of hemorrhage (Fig. 2 E–H). Facial nerve palsy and hearing impairment persisted, but no other major deficits occurred, and the patient had a modified Rankin Scale score of 1. Discussion Intrameatal AICA aneurysms arise within the internal auditory canal and are closely related to the facial and vestibulocochlear nerves. The internal auditory artery commonly arises from the meatal segment of the AICA and supplies the inner ear and adjacent cranial nerves. Consequently, treatment is challenging because interruption of the AICA may cause brainstem or cerebellar infarction and cranial nerve deficits. Many meatal aneurysms are wide-necked, fusiform, or dissecting rather than truly saccular, often making preservation of the parent artery difficult [ 1 , 3 , 6 ]. Although parent artery–preserving strategies such as clipping or selective coil embolization are desirable [ 1 , 3 , 4 , 6 , 8 ], they are not always feasible. In such situations, surgical trapping combined with bypass, such as occipital artery–AICA bypass, has been reported [ 9 ]. Management becomes more challenging when a distal arteriovenous shunt is present. Pial AVFs are characterized by a direct arteriovenous connection without an intervening nidus and often demonstrate high-flow shunting. Increased hemodynamic stress in feeding arteries may lead to the formation of flow-related aneurysms. Although flow-related aneurysms associated with AVMs or dural AVFs involving the AICA have been reported [ 2 , 5 , 7 , 8 ], association with a cerebellar pial AVF appears to be extremely rare. The present case is unusual because it represents a flow-related aneurysm arising from the intrameatal AICA in association with a cerebellar pial AVF. Both the intrameatal AICA aneurysm and the associated pial AVF could potentially have caused the SAH. Although the bleeding source could not be conclusively identified, flow-related aneurysms are known to be prone to rupture because of increased hemodynamic stress in feeding arteries [ 2 , 5 , 7 , 8 ]. In this case, the arteriovenous shunt persisted after treatment of the aneurysm without subsequent rebleeding, suggesting that the aneurysm was the more likely source. Therefore, treatment aimed at securing the aneurysm was prioritized. Selective angiography showed no significant supply to normal cerebellar or brainstem territories from the involved AICA segment, supporting PAO despite the potential risk of cranial nerve deficits. PAO also contributed to reducing shunt flow from the distal pial AVF. Because residual shunting from the SCA feeder remained after embolization and could not be safely catheterized, Gamma Knife radiosurgery was performed to achieve complete obliteration. Neurological complications are relatively common after treatment of meatal AICA aneurysms because these lesions are closely related to the facial and vestibulocochlear nerves. Previous studies report cranial nerve deficits in up to 52% of treated cases [ 1 ]. Therefore, particularly in ruptured cases with SAH, the primary therapeutic goal should be prevention of rebleeding even if some neurological deficit cannot be avoided. In this case, although facial nerve palsy and hearing impairment persisted after treatment, the patient achieved a favorable functional outcome with a modified Rankin Scale score of 1. The combined endovascular and radiosurgical strategy successfully prevented rebleeding and achieved complete obliteration of the arteriovenous shunt. Conclusion Intrameatal AICA aneurysms may occur as flow‑related lesions associated with distal pial AVFs. In such complex vascular conditions, a multimodality approach combining endovascular embolization and stereotactic radiosurgery may offer an effective strategy for achieving complete obliteration while minimizing the risk of rebleeding. Declarations Ethics approval This study was approved by the institutional review board of our hospital. Informed consent Written informed consent for publication of this information and accompanying images was obtained from the patient. Competing interests The authors declare no competing interests. Author Contribution H.M. conceived the study and wrote the main manuscript text. Y.Y. and A.O. collected clinical data. H.M. prepared the figures. H.M. and Y.Y. supervised the study. All authors reviewed the manuscript. References Lv X, Ge H, He H et al (2016) Anterior inferior cerebellar artery aneurysms: Segments and results of surgical and endovascular managements. Interv Neuroradiol 22:643–648. https://doi.org/10.1177/1591019916656474 Lee SJ, Koh JS, Ryu CW, Lee SH (2012) Ruptured intrameatal aneurysm of the anterior inferior cerebellar artery accompanying an arteriovenous malformation: A case report. Cerebellum 11(3):808–812. https://doi.org/10.1007/s12311-011-0349-z Liang B, Brammeier T, Huang J, Benardete EA (2020) Plugged Anterior Inferior Cerebellar Artery Aneurysm Causing Facial Palsy, Hearing Loss, and Subarachnoid Hemorrhage Treated by a Translabyrinthine Approach. Cureus 25(12):e12282. https://doi.org/10.7759/cureus.12282 Gao W, Liu P, Deng G, Li Z (2021) Fully Endoscope-Controlled Clipping Ruptured Intrameatal Anterior Inferior Cerebellar Artery Aneurysm: Report of 2 Cases. J Craniofac Surg 32(5):e470–e472. https://doi.org/10.1097/SCS.0000000000007434 Liu DD, Kurland DB, Ali A et al (2022) Pial brainstem artery arteriovenous malformation with flow-related intracanalicular aneurysm masquerading as vestibular schwannoma: illustrative case. J Neurosurg Case Lessons 18(3):CASE22208. https://doi.org/10.3171/CASE22208 Benjamin T, Jiam NT, Cooke D et al (2022) Anterior Inferior Cerebellar Artery Aneurysm Mimicking a Vestibular Schwannoma. Cureus 14(2):e21807. https://doi.org/10.7759/cureus.21807 Agarwal U, Parthasarathy R, Singla RS, Bhatter P (2026) AICA aneurysm–related subarachnoid hemorrhage in a dural AVF. J Clin Neurosci 146:111880. https://doi.org/10.1016/j.jocn.2026.111880 Hou K, Xu K, Chen X et al (2020) Endovascular treatment for the flow-related aneurysm originating from an anterior inferior cerebellar artery supplying the cerebellar arteriovenous malformation. Interv Neuroradiol 26:566–574. https://doi.org/10.1177/1591019920954082 Srinivasan VM, Labib MA, Lawton MT (2026) Occipital Artery to a3 Anterior Inferior Cerebellar Artery Bypass With Distal Occlusion of an Intrameatal a2 Fusiform Aneurysm. Oper Neurosurg 30(2):337–338. https://doi.org/10.1227/ons.0000000000001680 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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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-9110986","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":610026857,"identity":"dc4934d3-c2f8-4dd4-bc63-7b62ae9b4dbd","order_by":0,"name":"Hiroaki Matsumoto","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIiWNgGAWjYBACA2YQeUACyq1gYGCDsNiI0QJinSFGC5g8wADRwthGhMPM2XkfPvhxxoJBt/384c+88w5H80k3MH74wcCXh0uLZTO7sWHPDQkGszPJbNK82w7ntskcYJbsYWArxumww2xsEjwfJOq3HUhmYwZrkUhgkAb6JbEBjxbJPx+Atpx/zPyZdw5YC/NvQlqkeUAOu5HMIM3bANbCRsgWZmOZMyAtj80k5xxLB2pJbLPsMcDjl/PHGB++OVYHdFji4w9vaqxz589IPnzjR8UxnCGGDTACnWRwLIEULWBQQ7qWUTAKRsEoGK4AAMKMUIVaHEZ2AAAAAElFTkSuQmCC","orcid":"","institution":"Cerebrovascular Research Institute, Yoshida Hospital","correspondingAuthor":true,"prefix":"","firstName":"Hiroaki","middleName":"","lastName":"Matsumoto","suffix":""},{"id":610026858,"identity":"b4fcc010-8fbb-46b6-9e3b-c8685ca93ccc","order_by":1,"name":"Yasunori Yoshida","email":"","orcid":"","institution":"Cerebrovascular Research Institute, Yoshida Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yasunori","middleName":"","lastName":"Yoshida","suffix":""},{"id":610026859,"identity":"20f1dc5b-5f64-4ece-a04d-d5d2cf100655","order_by":2,"name":"Akihiro Okada","email":"","orcid":"","institution":"Cerebrovascular Research Institute, Yoshida Hospital","correspondingAuthor":false,"prefix":"","firstName":"Akihiro","middleName":"","lastName":"Okada","suffix":""},{"id":610026860,"identity":"31080242-ff42-4896-a4b1-d3405d5ac6bc","order_by":3,"name":"Hiroaki Minami","email":"","orcid":"","institution":"Cerebrovascular Research Institute, Yoshida Hospital","correspondingAuthor":false,"prefix":"","firstName":"Hiroaki","middleName":"","lastName":"Minami","suffix":""},{"id":610026861,"identity":"145dc110-91bf-42a1-b5f5-671ae7a529d4","order_by":4,"name":"Yasuhisa Yoshida","email":"","orcid":"","institution":"Cerebrovascular Research Institute, Yoshida Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yasuhisa","middleName":"","lastName":"Yoshida","suffix":""}],"badges":[],"createdAt":"2026-03-13 06:38:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9110986/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9110986/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105350405,"identity":"c979efd7-c479-4487-b61f-d943c715d83a","added_by":"auto","created_at":"2026-03-25 05:40:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2930540,"visible":true,"origin":"","legend":"\u003cp\u003eImaging findings demonstrating an intrameatal anterior inferior cerebellar artery (AICA) aneurysm and associated cerebellar pial arteriovenous fistula.\u003c/p\u003e\n\u003cp\u003e(A) Non-contrast computed tomography on admission showing subarachnoid hemorrhage predominantly in the posterior fossa.\u003c/p\u003e\n\u003cp\u003e(B) Time-of-flight magnetic resonance angiography source image suggesting a small aneurysm within the right internal auditory canal (arrow).\u003c/p\u003e\n\u003cp\u003e(C, D) Conventional digital subtraction angiography (DSA) of the left vertebral artery, performed because the right vertebral artery was hypoplastic. DSA shows a right intrameatal aneurysm of the AICA and an associated cerebellar arteriovenous shunt located at the border between the brainstem and cerebellum without an intervening nidus, draining via the superior and inferior hemispheric veins into the transverse sinus.\u003c/p\u003e\n\u003cp\u003e(C) Anteroposterior view. The arrowhead indicates the aneurysm, the red arrow the AICA, the blue arrow a feeder from brainstem perforating arteries, and the black arrow a feeder from the superior cerebellar artery (SCA).\u003c/p\u003e\n\u003cp\u003e(D) Lateral view demonstrating the intrameatal aneurysm (arrow). The blue arrowhead indicates the superior hemispheric vein and the red arrowhead the inferior hemispheric vein.\u003c/p\u003e\n\u003cp\u003e(E) Three-dimensional rotational digital subtraction angiography (3D-DSA) demonstrating a small aneurysm arising from the intrameatal segment of the right AICA (arrow).\u003c/p\u003e\n\u003cp\u003e(F, G) Selective angiography of the right AICA.\u003c/p\u003e\n\u003cp\u003e(F) Anteroposterior view demonstrating the intrameatal aneurysm (arrow) arising from the AICA.\u003c/p\u003e\n\u003cp\u003e(G) Lateral view demonstrating the intrameatal aneurysm (arrow) and an arteriovenous shunt without an intervening nidus. The shunt drains into the superior and inferior hemispheric veins. No normal perfusion of the brainstem or cerebellum is identified.\u003c/p\u003e\n\u003cp\u003e(H, I) Contrast-enhanced magnetic resonance imaging demonstrating a shunt at the border between the right brainstem and cerebellum, without a clearly identifiable nidus. (H, axial view; I, coronal view)\u003c/p\u003e\n\u003cp\u003e(J) Schematic illustration summarizing the angioarchitecture of the lesion.\u003c/p\u003e\n\u003cp\u003eAn intrameatal aneurysm arises from the right AICA. The cerebellar pial arteriovenous fistula is supplied by the AICA, brainstem perforators, and the SCA, and drains via the superior and inferior hemispheric veins into the transverse sinus and subsequently the sigmoid sinus.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-9110986/v1/5d8df206cb591595ebd03284.png"},{"id":105350395,"identity":"e1748f70-2d33-4002-88ed-62d7c0240fae","added_by":"auto","created_at":"2026-03-25 05:40:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5041920,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Postprocedural computed tomography demonstrating coils within the right internal auditory canal (red circle), confirming the intrameatal location of the aneurysm.\u003c/p\u003e\n\u003cp\u003e(B, C) Postprocedural digital subtraction angiography (DSA) demonstrating a residual arteriovenous shunt supplied by the superior cerebellar artery (red circle). The arrows indicate the superior and inferior hemispheric veins. (B, anteroposterior view; C, lateral view)\u003c/p\u003e\n\u003cp\u003e(D) Gamma Knife radiosurgery treatment planning using DSA and contrast-enhanced magnetic resonance imaging for targeting the residual arteriovenous shunt. The lesion was irradiated with a marginal dose of 18 Gy (maximum dose, 32.7 Gy).\u003c/p\u003e\n\u003cp\u003e(E–H) Follow-up DSA after Gamma Knife radiosurgery demonstrating complete obliteration of the pial arteriovenous fistula. (E, F, anteroposterior views; G, H, lateral views)\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-9110986/v1/c866d5e6cdbe5dd32e5fdbc8.png"},{"id":105350439,"identity":"8044ae8c-14f3-4de7-8767-bae056f2c3bb","added_by":"auto","created_at":"2026-03-25 05:41:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8123978,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9110986/v1/e8a4a444-34bd-45ba-88c4-e83b35f02306.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Flow-related Intrameatal AICA Aneurysm Associated with a Cerebellar Pial AVF: Diagnostic Features and Multimodality Management","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAneurysms arising from the anterior inferior cerebellar artery (AICA) are rare, representing less than 1% of all intracranial aneurysms [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Among these, aneurysms located within the internal auditory canal (intrameatal AICA aneurysms) are particularly uncommon, with only a few reported cases [\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFlow-related aneurysms may arise in association with intracranial arteriovenous shunts, most often with arteriovenous malformations (AVMs) or dural arteriovenous fistulas (AVFs), whereas their occurrence in the AICA is rare [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Association with a distal pial AVF is especially uncommon.\u003c/p\u003e \u003cp\u003eWe report a case of a flow-related intrameatal AICA aneurysm associated with a cerebellar pial AVF that required a multimodality treatment strategy.\u003c/p\u003e"},{"header":"Case description","content":"\u003cp\u003eA 68-year-old woman presented with sudden onset of severe headache and vomiting. Computed tomography revealed subarachnoid hemorrhage (SAH) predominantly in the posterior fossa (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). On admission, the patient had mild disturbance of consciousness without facial nerve palsy or hearing impairment, and her clinical grade was Hunt and Kosnik grade 2.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMagnetic resonance angiography did not clearly demonstrate an aneurysm, but time‑of‑flight source images suggested a small lesion in the right internal auditory canal (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eDigital subtraction angiography demonstrated an intrameatal AICA aneurysm with an associated cerebellar arteriovenous shunt (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC\u0026ndash;G). No nidus was identified. Contrast‑enhanced magnetic resonance imaging showed a focal shunt point at the brainstem\u0026ndash;cerebellar border rather than within the dura (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eH, I), supporting the diagnosis of a cerebellar pial AVF. The lesion was supplied by three arterial feeders: the AICA, brainstem perforators, and the superior cerebellar artery (SCA) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eJ). The aneurysm was considered a flow‑related lesion induced by hemodynamic stress from the distal shunt.\u003c/p\u003e \u003cp\u003eSelective AICA angiography showed no significant supply to normal cerebellar or brainstem territories from the involved segment (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eE, F).\u003c/p\u003e \u003cp\u003eThe aneurysm measured approximately 2.5 mm and lacked a clearly defined neck, making selective coil embolization technically difficult. Reduction of shunt flow from the pial AVF was deemed necessary. Although facial nerve palsy and hearing impairment were possible, the risk of cerebellar or brainstem infarction was considered low. Therefore, parent artery occlusion (PAO) of the AICA using coils was performed to secure the aneurysm and reduce shunt flow from the pial AVF (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). The brainstem perforating feeder was then embolized with N‑butyl cyanoacrylate, but the SCA feeder could not be treated because catheter navigation was difficult.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBecause a residual shunt persisted at the 3-month follow-up after endovascular treatment, Gamma Knife radiosurgery was performed (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB\u0026ndash;D). Follow-up imaging demonstrated complete obliteration of the AVF without recurrence of hemorrhage (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE\u0026ndash;H). Facial nerve palsy and hearing impairment persisted, but no other major deficits occurred, and the patient had a modified Rankin Scale score of 1.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIntrameatal AICA aneurysms arise within the internal auditory canal and are closely related to the facial and vestibulocochlear nerves. The internal auditory artery commonly arises from the meatal segment of the AICA and supplies the inner ear and adjacent cranial nerves. Consequently, treatment is challenging because interruption of the AICA may cause brainstem or cerebellar infarction and cranial nerve deficits. Many meatal aneurysms are wide-necked, fusiform, or dissecting rather than truly saccular, often making preservation of the parent artery difficult [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Although parent artery\u0026ndash;preserving strategies such as clipping or selective coil embolization are desirable [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], they are not always feasible. In such situations, surgical trapping combined with bypass, such as occipital artery\u0026ndash;AICA bypass, has been reported [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eManagement becomes more challenging when a distal arteriovenous shunt is present. Pial AVFs are characterized by a direct arteriovenous connection without an intervening nidus and often demonstrate high-flow shunting. Increased hemodynamic stress in feeding arteries may lead to the formation of flow-related aneurysms. Although flow-related aneurysms associated with AVMs or dural AVFs involving the AICA have been reported [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], association with a cerebellar pial AVF appears to be extremely rare. The present case is unusual because it represents a flow-related aneurysm arising from the intrameatal AICA in association with a cerebellar pial AVF.\u003c/p\u003e \u003cp\u003eBoth the intrameatal AICA aneurysm and the associated pial AVF could potentially have caused the SAH. Although the bleeding source could not be conclusively identified, flow-related aneurysms are known to be prone to rupture because of increased hemodynamic stress in feeding arteries [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In this case, the arteriovenous shunt persisted after treatment of the aneurysm without subsequent rebleeding, suggesting that the aneurysm was the more likely source. Therefore, treatment aimed at securing the aneurysm was prioritized.\u003c/p\u003e \u003cp\u003eSelective angiography showed no significant supply to normal cerebellar or brainstem territories from the involved AICA segment, supporting PAO despite the potential risk of cranial nerve deficits. PAO also contributed to reducing shunt flow from the distal pial AVF. Because residual shunting from the SCA feeder remained after embolization and could not be safely catheterized, Gamma Knife radiosurgery was performed to achieve complete obliteration.\u003c/p\u003e \u003cp\u003eNeurological complications are relatively common after treatment of meatal AICA aneurysms because these lesions are closely related to the facial and vestibulocochlear nerves. Previous studies report cranial nerve deficits in up to 52% of treated cases [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Therefore, particularly in ruptured cases with SAH, the primary therapeutic goal should be prevention of rebleeding even if some neurological deficit cannot be avoided.\u003c/p\u003e \u003cp\u003eIn this case, although facial nerve palsy and hearing impairment persisted after treatment, the patient achieved a favorable functional outcome with a modified Rankin Scale score of 1. The combined endovascular and radiosurgical strategy successfully prevented rebleeding and achieved complete obliteration of the arteriovenous shunt.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIntrameatal AICA aneurysms may occur as flow‑related lesions associated with distal pial AVFs. In such complex vascular conditions, a multimodality approach combining endovascular embolization and stereotactic radiosurgery may offer an effective strategy for achieving complete obliteration while minimizing the risk of rebleeding.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eEthics approval\u003c/h2\u003e \u003cp\u003eThis study was approved by the institutional review board of our hospital.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eInformed consent\u003c/strong\u003e \u003cp\u003e Written informed consent for publication of this information and accompanying images was obtained from the patient.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting interests\u003c/strong\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eH.M. conceived the study and wrote the main manuscript text. Y.Y. and A.O. collected clinical data. H.M. prepared the figures. H.M. and Y.Y. supervised the study. All authors reviewed the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLv X, Ge H, He H et al (2016) Anterior inferior cerebellar artery aneurysms: Segments and results of surgical and endovascular managements. Interv Neuroradiol 22:643\u0026ndash;648. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1177/1591019916656474\u003c/span\u003e\u003cspan address=\"10.1177/1591019916656474\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee SJ, Koh JS, Ryu CW, Lee SH (2012) Ruptured intrameatal aneurysm of the anterior inferior cerebellar artery accompanying an arteriovenous malformation: A case report. 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Oper Neurosurg 30(2):337\u0026ndash;338. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1227/ons.0000000000001680\u003c/span\u003e\u003cspan address=\"10.1227/ons.0000000000001680\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\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":true,"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":"anterior inferior cerebellar artery, intrameatal aneurysm, pial arteriovenous fistula, flow-related aneurysm, endovascular treatment, Gamma Knife radiosurgery","lastPublishedDoi":"10.21203/rs.3.rs-9110986/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9110986/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIntrameatal aneurysms of the anterior inferior cerebellar artery (AICA) are extremely rare, particularly when associated with distal arteriovenous shunts. We report a ruptured intrameatal AICA aneurysm associated with a cerebellar pial arteriovenous fistula (AVF) and describe its imaging characteristics and multimodality management. A 68-year-old woman presented with sudden onset of severe headache and vomiting. Computed tomography revealed subarachnoid hemorrhage predominantly in the posterior fossa. Digital subtraction angiography demonstrated a small intrameatal AICA aneurysm and a cerebellar arteriovenous shunt without an intervening nidus, consistent with a pial AVF supplied by the AICA, brainstem perforators, and the superior cerebellar artery. The aneurysm was considered a flow-related lesion caused by increased hemodynamic stress from the distal shunt. Parent artery occlusion of the AICA was performed to secure the aneurysm and reduce shunt flow, followed by Gamma Knife radiosurgery for the residual AVF. Follow-up angiography confirmed complete obliteration.\u003c/p\u003e","manuscriptTitle":"Flow-related Intrameatal AICA Aneurysm Associated with a Cerebellar Pial AVF: Diagnostic Features and Multimodality Management","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-25 05:39:50","doi":"10.21203/rs.3.rs-9110986/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":"323ec7bb-3c73-45ba-bd32-ac001aba29b6","owner":[],"postedDate":"March 25th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-04-30T11:24:42+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-17T13:38:43+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-25 05:39:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9110986","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9110986","identity":"rs-9110986","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}