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.