The diagnosis and management of an expanding post-traumatic soft tissue cyst of the hip and groin.

A post-traumatic cyst is a rare complication of significant soft tissue trauma. It occurs at the junction between the subcutaneous fat and underlying fascia, when a large, subcutaneous haematoma fails to resolve, developing into a chronic, fluid-filled cyst, lined with fibrous tissue. This results in a swelling that persists for years, gradually increasing in size, often without causing significant discomfort to the patient. Clinically and radiologically these swellings may be mistaken for neoplastic lesions. They can be difficult to treat, are refractory to conservative management and have a high rate of recurrence following surgical excision. Careful monitoring and early treatment of persistent postoperative seroma is advocated.