Chronic expanding hematoma in the retroperitoneal space

Background Chronic expanding hematoma is a rare condition that occurs after surgery, trauma, or injury. It can occur anywhere in the body with the absence of trauma. Clinical findings, various modalities will help in the differential diagnosis. Hematomas are usually absorbed naturally and rarely cause serious problems. However, hematomas developing slowly without a history of trauma, surgery and bleeding disorders could be difficult to differentiate from soft tissue neoplasm. Our case showed the biggest chronic expanding hematoma in retroperitoneal space which resulted hydronephrosis due to the pressure of left ureter without any trauma. Case presentation A 69-year-old male patient presented at a hospital with a swollen lesion in the left flank. A mass 19 cm in diameter was detected in the retroperitoneal space on computed tomography. Chronic expanding hematoma, soft tissue tumor, or left renal artery aneurysm were suspected. Postoperative histopathological examination revealed the tumor to be a nonmalignant chronic expanding hematoma. No recurrence was observed within the 2-year follow-up period.