[Atypical neuroradiological features of microcystic meningioma: case report]

We report a rare case of microcystic meningioma presenting with atypical neuroradiological features. A 76-year-old woman was admitted to our hospital in October, 1996 because of head heaviness without obvious neurological deficits. Previous CT scan in 1989 revealed no abnormality, but a subsequent scan in 1992 showed a low-density area in the right frontal region. Since then the patient has been followed up as a case of cerebral infarction. At the time of the current admission, CT scan disclosed the low-density area as having grown to the size of 4 cm and heterogeneously enhanced after injection of contrast medium. On MRI the mass lesion was depicted as low-intensity on T1-weighted image and high-intensity on T2-weighted image. The mass was heterogeneously enhanced after administration of Gd-DTPA. Right internal and external carotid angiograms revealed neither tumor feeder nor tumor stain. Craniogram showed neither hyperostosis nor bone erosion, and yet bone scintigram demonstrated markedly increased uptake involving the right frontal bone near the tumor. At surgery the tumor was found to have originated from the dura in the right frontal convexity, which was well demarcated and separated from the surrounding brain tissue. Total removal designated as Simpson grade I procedure was accomplished. Light microscopy revealed abundant microcysts of varied size throughout the tumor tissue with the presence of whorl formation and psammoma body, but no malignancy was indicated. Electron microscopy further demonstrated interdigitation of the neighboring cell membranes, desmosomes, and intracytoplasmic filaments, which are pathognomonic findings of meningiomas. The microcysts were seen to reside in the extracellular spaces rather than in the cytoplasm. With these pathological findings, the tumor was finally diagnosed as microcystic meningioma.