Masson tumor (intravascular papillary endothelial hyperplasia) arising in a superficial temporal artery aneurysm

Masson tumor (intravascular papillary endothelial hyperplasia) is a rare proliferation of endothelial cells within the wall of a vessel, often thought to represent an aberrant resolution of a thrombosis. We describe the unique case of a 75-year-old man who presented to the clinic with a tender, spontaneous aneurysmal dilation of his left superficial temporal artery (STA). Only 8% of all STA aneurysms are believed to be spontaneous true aneurysms, with the majority being post-traumatic pseudoaneurysms. After successful surgical resection, pathologic examination demonstrated a Masson tumor within an STA aneurysm. This paper describes a case in which both rare entities were discovered and briefly outlines the diagnostic and therapeutic modalities available.