Intramural schwannoma involving a vein.

Schwannoma involving the blood vessels is a rare phenomenon. So far, only three cases of intravascular schwannoma have been described (all of which were intraluminal), and the origin of the schwannoma in such cases is not yet completely understood. Here, we describe a very rare intramural venous schwannoma in the subcutaneous right prepatellar area of a 31-year-old man. The schwannoma grew by enlarging and thickening the blood vessel wall, between two preserved layers of the vein. In some areas, there was erosion of the luminal layer, with fibrin apposed to the tumor. The tumor expressed S100 and was negative for CD31, CD34, desmin, and smooth muscle actin. The expression of p16 was preserved. Endothelial markers such as CD31 and Factor VIII showed the endothelial lining (which was D2-40-negative) above the tumor. Although degenerative atypia was present, there were no mitotic figures or necrosis identified.