Neoplastic angioendotheliomatosis. Histologic, immunohistochemical, and ultrastructural findings in two cases.

Two cases of neoplastic angioendotheliomatosis are described. Both patients presented with subacute development of dementia punctuated by focal neurologic signs. Postmortem examination in both cases disclosed a vasculocentric distribution of neoplastic cells in many organs. Two characteristic histologic patterns were seen: (1) distension of vascular spaces by free-floating, intraluminal cells and (2) asymmetric, subendothelial tumor growth. Intravascular tumor and secondary vascular changes were associated with microinfarcts in involved organs. Immunohistochemical localization of factor VIII-related antigen in the neoplastic cells of one case provides evidence for their endothelial origin. The neoplastic cells in both cases exhibited similar but nonspecific ultrastructural features. In addition, dramatic fine structural changes including the acquisition of numerous pinocytotic vesicles and bundles of fine filaments with periodic densities were found in the non-neoplastic endothelial cells.