Anterior inferior cerebellar artery aneurysms mimicking vestibular schwannomas.

Background And Purpose: Unruptured anterior inferior cerebellar artery (AICA) aneurysms are rare but potentially lethal cerebellopontine angle (CPA) lesions that may be misdiagnosed as vestibular schwannomas when they present with vestibulo-cochlear symptoms.

Methods: We report two cases of unruptured but symptomatic AICA aneurysms initially referred to us as atypical vestibular schwannomas requiring surgery. Two discriminant MR features are described.

Results: One patient refused treatment. The other was successfully treated by coil occlusion.

Conclusions: Caution is advised before suspecting a CPA mass to be a purely extra-canalicular schwannoma, given its extreme rarity. Deafness and cerebellar ischemia may be prevented if AICA aneurysms are correctly identified preoperatively. In the absence of specific arterial imaging, two MR features may distinguish them from vestibular schwannomas: (1) the absence of internal auditory canal enlargement and (2) the "blurry dot sign," representing blood flow artefacts on pre- and postcontrast studies.