Masson's tumor in the ulnar artery.

A healthy 30-year-old woman presented to the emergency department with a pulsatile right forearm mass and numbness of her fourth and fifth fingers. Duplex scan imaging revealed an ulnar artery aneurysm with intramural thrombus. After resection, histopathology revealed intravascular papillary endothelial hyperplasia, also known as Masson's tumor, a rare but benign vascular neoplasm. Local resection of the tumor with vascular reconstruction is curative and resulted in resolution of her neurologic symptoms. To our knowledge, this is the first reported case of a Masson's tumor occurring in an ulnar artery.