Anterior Inferior Cerebellar Artery Aneurysm Mimicking a Vestibular Schwannoma.

Anterior inferior cerebellar artery (AICA) aneurysms are rare pathologies that may present with hearing loss, facial paralysis, vertigo, and tinnitus. Otologic symptoms at the time of presentation may prompt physicians to order an MRI, which can lead to the misdiagnosis of AICA aneurysms as vestibular schwannomas. We discuss the case of a 27-year-old female who presented with sudden-onset vertigo and right-sided hearing loss. She was found to have a right homogeneously enhancing internal auditory canal (IAC) mass abutting the vestibular nerve on post-gadolinium T1 MRI two hours after the presentation, which was initially diagnosed as a vestibular schwannoma. Serial T1 MRI highlighted the evolution of blood products within this mass by presenting as bright at two days and dark at two months after presentation. Profound ipsilateral sensorineural hearing loss and absent vestibulocochlear function were confirmed on audiometry and vestibular testing, respectively. The diagnostic cerebral angiogram was complicated by an iatrogenic right mid-cervical vertebral artery dissection, and the patient ultimately underwent successful embolization two months after presentation with the resolution of all presenting symptoms except right-sided hearing loss. Early recognition and treatment of an AICA aneurysm may help prevent associated vascular complications, and they should be considered as part of the differential diagnosis for IAC lesions despite their rarity.