A woman with fever and a painful hip and lower back

A 66-year-old woman presented with fever and acute pain in her lower back and left hip. She used prednison for arteriitis temporalis. Abdominal radiography revealed no signs of free intraperitoneal gas, but instead a radiolucent area below the spleen suggesting free retroperitoneal gas. This was confirmed by CT-scan of the abdomen and surgery, when a diverticulitis of the colon descendens with retroperitoneal perforation was diagnosed.