The vestibular schwannoma (VS) is the most common neoplastic mass of the cerebellopontine angle (CPA). Over 95% of these masses are solitary and sporadic neoplasms. The remaining 4-5% are part of NF2, and in that disease are bilateral in at least 2/3 of patients. VS almost invariably enhances. Small lesions are homogeneous, larger lesions are heterogeneous due to benign cystic degeneration, and some lesions create a secondary "arachnoid cyst".

The second most common CPA mass is the meningioma, an enhancing hemispheric lesion with a broad base of dural attachment.

The third most common mass in the CPA is the epidermoid inclusion cyst.

MRI: Often isointense or slightly hypointense to brain on T1W images, they may become heterogeneously bright on T2 - usually explained by the loose or myxoid (watery) "Antoni B" areas seen histologically.

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