Cerebellopontine Angle Arachnoid Cyst Presenting as Positional Vertigo

Introduction: Arachnoid cysts are intra-arachnoidal collections of cerebrospinal fluid that are thought to be mostly congenital in origin. They can occur at different intracranial sites, including the cerebellopontine angle (CPA). The incidence of arachnoid cysts is around 1% of all intracranial lesions. Case Report: This is a case of a CPA arachnoid cyst in a 34-year-old woman complaining of recurrent short episodes of vertigo associated with head movement. There was no history of tinnitus, ottorhea, nausea, dizziness, or hearing impairment. Otoneurologic examination including Dix-Hallpike maneuver was unremarkable apart from a positive Unterberger's test. The pure tone audiogram was normal. Electronystagmography with alternate binaural, bithermal calorics showed a reduced right vestibular response. Brainstem evoked responses (BSER) showed prolonged I–III and I–V wave latencies. Enhanced MRI scan revealed a 2.2-cm arachnoid cyst on the right CPA. A wait-and-see policy was adopted. Discussion and Conclusion: CPA arachnoid cysts in adult patients are a well-recognized clinical entity and may either cause various otoneurological symptoms or be asymptomatic. MRI scan is diagnostic and can exclude other CPA lesions. Once the diagnosis is established a wait-and-see policy can be safely adopted in the majority of cases, unless there are severe vestibular or other space occupying symptoms. If this is the case, surgical fenestration or excision of the cyst should be performed.