BACKGROUND: Chronic expanding hematoma is characterized by a continuous growing hematoma lesion.

CASE REPORT: The present case is of a patient who had undergone resection of synovial sarcoma in the posterior thigh and subsequent intraoperative radiation to the region at the age of 18 years. The patient observed swelling at the surgical site 31 years later at the age of 49 years. Magnetic resonance imaging revealed a growing hematoma with a cystic appearance. Partial resection of the wall and electrocoagulation of bleeding from the remaining wall were performed at the age of 50 years.

CONCLUSIONS: Chronic expanding hematoma occurred as a late complication of tumor treatment.

Keywords: Hematoma, Magnetic Resonance Imaging, Radiation, Sarcoma, Synovial, Chronic Disease, Intraoperative Care, Radiotherapy, Adjuvant, Soft Tissue Neoplasms, Thigh, Time Factors