Nontraumatic Proximal Ulnar Artery Pseudoaneurysm Mimicking a Soft Tissue Tumor in Image Modality.

Aneurysm of the proximal ulnar artery is extremely rare. Ultrasonography, computed tomography, and magnetic resonance imaging generally provide accurate diagnosis of aneurysm. A 29-year-old woman who had undergone an excision biopsy of a mass in her right arm by an orthopedic surgeon was referred to our department. We resected the mass and interposed it with a reversed great saphenous vein. Histopathological examination suggested that the mass was a pseudoaneurysm consisting of organized thrombi with recanalization. Clinicians should be aware of the possibility of misdiagnosis of soft tissue tumor in cases of pseudoaneurysm, especially if imaging examination reveals a density consistent with organized thrombus with recanalization.