Pial brainstem artery arteriovenous malformation with flow-related intracanalicular aneurysm masquerading as vestibular schwannoma: illustrative case

BACKGROUND: Lesions of the internal auditory canal presenting with partial hearing loss are almost always vestibular schwannomas (VSs). Intracanalicular anterior inferior cerebellar artery (AICA) aneurysms are extremely rare but can mimic VS based on symptoms and imaging. The authors report the case of a flow-related intracanalicular AICA aneurysm from a pial brainstem arteriovenous malformation (AVM) masquerading as VS. OBSERVATIONS: A 57-year-old male with partial left-sided hearing loss and an intracanalicular enhancing lesion was initially diagnosed with VS and managed conservatively at an outside institution with surveillance imaging over 3 years. When he was referred for VS follow-up, new imaging raised radiological suspicion for vascular pathology. Cerebral angiography revealed a small pial AVM located at the trigeminal root entry zone with an associated flow-related intracanalicular AICA aneurysm. The AVM was obliterated with open surgery, during which intraoperative angiography confirmed no AVM filling, preservation of the AICA, and no further aneurysm filling. LESSONS: Intracanalicular AICA aneurysms and other lesions, including cavernous malformations, can mimic radiographic features of VS and present with hearing loss or facial weakness. Modern vascular neurosurgical techniques such as endovascular intervention and open surgery in a hybrid operating room allowed definitive management of both lesions without untoward morbidity.