Kaposi-like infantile hemangioendothelioma. A distinctive vascular neoplasm of the retroperitoneum.

Retroperitoneal soft-tissue tumors are rare in infancy. In this report, we describe a distinctive hemangioendothelioma occurring in the retroperitoneum of a 10-month-old baby girl. This lesion was complicated by obstructive jaundice, intestinal obstruction, and thrombocytopenia (Kasabach-Merritt syndrome) leading to intracranial hemorrhage. The microscopic features of this tumor, characterized by infiltrative lobules of spindle cells and capillaries, are distinct from those of other well-recognized vasoformative tumors. In some areas, the tumor shows a striking resemblance to Kaposi's sarcoma; criss-crossing fascicles of spindle cells are interspersed with narrow vascular spaces, but PAS-positive hyaline globules are absent. The tumor can also be distinguished from the cellular hemangioma of childhood by its well-formed spindle cell fascicles. Several histologically similar cases have been reported. All of them occurred in the retroperitoneum of infants and were frequently complicated by Kasabach-Merritt syndrome. We therefore propose the designation "Kaposi-like infantile hemangioendothelioma" for this unusual neoplasm.