Malignant angioendothelioma. Cytologic, histologic and ultrastructural findings.

Cells of a malignant angioendothelioma in pleural fluid were studied by light and electron microscopy. They occurred singly and clustered, with peripheral, pleomorphic nuclei containing finely particulate chromatin and one or two nucleoli. The cytoplasm was pale and finely vacuolated. Ultrastructural findings were those of endothelial cells: cytoplasmic pseudopodia, tight junctional complexes, cytoplasmic filaments and pinocytotic vesicles.