Acquired progressive lymphangioma.

Acquired progressive lymphangioma is rare and can histologically mimic well-differentiated angioendothelioma. In a 9-year-old boy with acquired progressive lymphangioma, we demonstrated that the neoplasm consists of at least a vascular component and a smooth muscle component. The presence of type IV collagen around many vascular channels suggests that an intermediate stage of differentiation between blood vessels and lymphatics may be present. Our findings indicate that acquired progressive lymphangioma is most likely a complex hamartoma composed of vascular channels and smooth muscle.