Microcystic meningioma: clinicopathological features of 6 cases.

The clinical and morphological features of 6 patients with unusual meningiomas with extensive microcystic formation are presented. There were 4 males and 2 females, ranging in age from 30 to 64 years. The clinical and neuro-imaging features of these tumours were identical with those of meningiomas in general. Morphological examinations disclosed that the tumour cells in 4 cases had many ultrastructural characteristics in common with the arachnoid cap cells, viz. prominent and complex interdigitation of the fine cytoplasmic processes, many desmosomes, and intracytoplasmic microfilaments. In contrast, the tumour cells of 2 cases had characteristic structures in common with trabecular arachnoid cells, viz. stellate in shape, a small number of intracytoplasmic filaments, relatively thick cytoplasmic processes, and occasional desmosomes. The tumour cells in these 2 cases were considered to recapitulate the subarachnoid structure and showed microcystic appearance. Although the histogenesis of microcysts in meningiomas is considered not to be uniform, the biological behaviour of these 6 tumours corresponded to those of meningiomas in general.