Cystic meningiomas--an update.

Eighteen unusual cases of intracranial meningioma associated with a cyst are considered. Three patients were operated upon before the introduction of computed tomography scanning, and the discovery of a peritumoral cyst was unexpected. Among 15 patients studied with computed tomography, 8 had a peritumoral cyst, 6 had an intratumoral cyst, and 1 had a totally cystic meningioma (hypodense on computed tomography). Computed tomography permitted a correct preoperative diagnosis only in four cases. In six additional cases diagnosis was reached by selective angiographic studies. In the remaining cases diagnosis was impossible or incorrect. Different pathogenetic mechanisms underlie different radiologic patterns. The authors comment on the complex processes that lead to cyst formation in meningiomas and stress the necessity of an accurate preoperative study to avoid misdiagnosis.