Infected retroperitoneal cystic lymphangioma masquerading as psoas abscess.

A 2-year-old male is described who presented with fever, fixed flexion deformity of the right hip and a tender mass in the right iliac fossa. A clinical diagnosis of psoas abscess was made. Abdominal ultrasound was suggestive of an echogenic retroperitoneal cyst but could not accurately determine the nature of the cyst.