Cystic appearance of meningiomas: considerations on a series of 12 patients.

Twelve patients affected with meningiomas with a fluid component are reviewed. Six presented with intratumoral cysts and 6 with extratumoral fluid collections that in 3 cases were of clear CSF. The formation mechanism of the two types are quite different. Intratumoral cysts are caused by biological changes within the tumor, while the extratumoral ones appear to be secondary to local hydrodynamic changes and CSF reabsorption disturbances. The CT (computerized tomography) scan may be equivocal either for the diagnosis of the meningioma or, once the meningioma is suspected, for identifying the type of cyst involved. The angiography is useful for a correct preoperative diagnosis that, once suspected, can be frequently made.