Cystic meningiomas, a diagnostic and pathogenic challenge.

A 55-year-old woman presented with focal seizures, then rapidly evolving hemiplegia. Brain CT and MRI showed a large cystic lesion of the right frontal lobe with a small enhancing nodule adjacent to the dura. The nodule corresponded to a meningioma on pathological examination, and the operative findings suggested that the cyst was due to local entrapment of CSF by the tumor and its arachnoid adhesions. The rapid clinical deterioration was probably due to the rapid expansion of the cyst volume. Pathogenesis and unusual radiological appearances of cystic meningiomas are discussed.