[Electron microscopic study of metastatic hemangiopericytic meningioma]

Electron microscopic observations in a case of metastatic hemangiopericytic meningioma was presented. Cell origin of this tumor was discussed in detail from the point of the leiomyoblastic differentiation. The patient was a 49-year-old woman who was operated four times in the past for the cerebellar tentorial and the left parasagittal tumors. Six years after the first operation, metastatic lesions were found in the rib, the liver, the cervical vertebra and the sternum. Specimens were prepared from the intracranial and the rib tumors. On light microscopy the tumor cells with large nuclei and scant cytoplasm were proliferated around an endothelial-lined capillaries constituting obstructive or distended lumens. Mitoses and focal necrosis also existed. On electron microscopy the tumor cells were ovoid or ellipsoidal and had large irregular-shaped nuclei with conspicuous nucleoli. Knob-ended cytoplasmic processes occupying among tumor cells formed interdigitation. Microorganellae such as rough endoplasmic reticulum, Golgi apparatus, and mitochondriae were well developed. Glycogen granules were abundant. Some cells had a large number of 5-7nm microfilaments. Occasionally these filaments condensed into the dense body-like structure parallel to the cell surface. Pinocytic vesicles were not observed. Vascular channels varied in shape. The capillaries were lined by an endothelial cell. The endothelium had pinocytic vesicles under the plasmalemma and intracytoplasmic processes projecting into the vascular lumen. The neoplasmic cells and capillaries were surrounded by the basement membrane-like substance which consisted of amorphous and fibrous components.(ABSTRACT TRUNCATED AT 250 WORDS)