[Masson tumour: a benign vascular lesion]. / Massontumor: een benigne vaatafwijking.

A 39-year-old woman presented with a swelling on the left inner thigh. Physical examination was suggestive of a lipoma. However, peri-operatively the lump appeared to be a vascular tumour arising from the great saphenous vein. Histological examination revealed a benign Masson tumour, a rare vascular tumour that is characterized by endothelial hyperplasia and the presence of papillary structures. It is of clinical importance to distinguish the benign Masson tumour from a malignant angiosarcoma.