Cellular hemangiomas ("hemangioendotheliomas") in infants. Light microscopic, immunohistochemical, and ultrastructural observations.

Cellular hemangiomas of infancy, also known as "infantile hemangioendotheliomas," are benign tumors whose dense cellularity may lead to confusion with soft tissue sarcomas. Ultrastructural and immunohistologic study revealed considerable cellular heterogeneity in these lesions despite the monomorphous appearance revealed by routine histologic preparations. Pericytes and endothelial cells are predominant, but fibroblasts and mast cells are regularly present in these tumors. An interstitially located cell of uncertain identification, expressing factor XIIIa and a macrophage marker, not previously noted, comprises an important segment of the cell population. The cell composition reflects the dynamic potential of these lesions, whose natural tendency is to grow, then to become stable, and finally to involute.