Acquired mirror-image cerebellopontine angle arachnoid cysts: case report.

Arachnoid cysts are neurosurgical entities that have long been considered to be congenital in origin. Many examples in the literature suggest that there is a subgroup of arachnoid cysts that are required. The authors present the clinical history of a 17-month-old girl who developed two cerebellopontine angle arachnoid cysts after posterior fossa surgery for a brain tumor. After surgical excision of the tumor the child developed a left cerebellopontine angle cyst. This was treated through a suboccipital craniectomy by evacuating the cyst and excising the cyst wall. Two months later the child developed a second right-sided cerebellopontine angle cyst. It was treated by inserting a cystoperitoneal shunt. This article presents the case with radiological evidence of the acquired nature of the cysts. It also includes a brief review of the clinical presentation, pathogenesis, radiological evaluation, and surgical treatment of arachnoid cysts with emphasis on those occurring in the posterior fossa.