Chronic expanding hematoma of the left flank mimicking a soft-tissue neoplasm

Soft-tissue hematomas are a common clinical entity often associated with trauma, surgery, and bleeding disorders. In the majority of cases, soft-tissue hematomas acutely appear and spontaneously resolve, but sometimes, they present as swellings that slowly expand and progressively increase with time. We present a case of a 70-year-old man with chronic expanding hematoma of the left flank without any history of recent trauma or other medical disease. The diagnosis could not be confirmed on imaging features alone, so the patient was taken to surgery for open biopsy and excision. In patients with slowly growing extremity masses without recent trauma or chronic medical disorders, the differential diagnosis becomes challenging, and chronic expanding hematoma should be considered in addition to soft-tissue sarcomas and other malignancies.