The patient is a 68-year-old man with a 3-year history of a slowly enlarging mass on his left posterior thigh. He reports that he had a penetrating injury to the thigh while he was in the military over 20 years ago. Radiographs showed a large soft tissue density without underlying bone involvement. An MRI of the thigh demonstrated a 12 cm × 16-cm mass, with heterogeneous signal, which enhanced after administration of contrast. Staging studies, which included CTs of his chest, abdomen, and pelvis, were negative. A Tc-99m MDP scan was performed to evaluate for bone metastasis and showed peripheral enhancement of the mass without definite evidence of underlying bone involvement. The bone scan findings led to the suspicion of a pseudoaneurysm and the redirection of this patient's evaluation. An arteriogram was than performed to evaluate for a vascular etiology and was interpreted as being suspicious for a pseudoaneurysm. An open biopsy was performed, which did not show evidence of tumor. Evacuation of a hematoma and exploration were performed. A pseudoaneurysm was identified in the left superficial femoral artery and repaired. Copyright © 2006 by Lippincott Williams & Wilkins.