Synovial sarcoma mimicking a traumatic pseudoaneurysm in the upper extremity.

Synovial sarcomas are a rare but aggressive malignancy that primarily affects young patients. Diagnosis is often difficult and delayed due to its insidious onset, heterogenous presentation and mimicry of other pathologies. We present the case of a patient with a history of a slow-growing left arm mass that arose after a traumatic fracture of the humerus. Multimodal imaging was undertaken and reported the mass as being consistent with a vascular malformation of the brachial artery. The patient underwent surgical repair of the artery and intraoperative biopsies confirmed a diagnosis of synovial sarcoma. This case highlights the importance of maintaining suspicion for soft-tissue sarcomas in young patients presenting with a mass, and demonstrates the way in which these tumours may mimic other pathologies both clinically and radiologically. Early referral to a specialist sarcoma centre is key for further investigative workup.