Florid extravascular papillary endothelial hyperplasia (Masson's pseudoangiosarcoma) presenting as a soft-tissue sarcoma.

Papillary endothelial hyperplasia (also known as Masson's pseudoangiosarcoma) is a hyperplastic proliferation of endothelial cells that is usually an incidental finding within thrombosed dilated blood vessels or vascular tumors. Rare extravascular forms occur and can histologically closely mimic angiosarcoma. We report a case of extravascular papillary endothelial hyperplasia that extensively involved a large, traumatic, deep soft-tissue hematoma in a 19-year-old man and clinically presented as a soft-tissue sarcoma. We also summarize characteristics of 314 cases of papillary endothelial hyperplasia reported in the literature and identify 13 likely cases of the rare extravascular form.