Cerebellopontine angle arachnoid cyst harbouring ectopic neuroglia.

Arachnoid cysts are collections of cerebrospinal fluid covered by arachnoidal cells and collagen. They may have a congenital or acquired origin. We present the case of a 7-year-old boy with a cerebellopontine angle arachnoid cyst harbouring a portion of neuroglia. Microscopically, the cyst wall consisted of a delicate fibrovascular membrane lined by a layer of arachnoidal cells. A thin layer of glial tissue ran the whole length of the cyst wall. This finding supports a congenital origin for this case. Cerebellopontine angle arachnoid cysts harbouring neuroglia without ependymal elements are very rare lesions and may be successfully treated by surgical resection.