A 61 year old man presented with a ten day history of right sided non-colicky abdominal pain radiating to the back, and four episodes of fever with rigor, each of which lasted an hour. He had no other gastrointestinal or urinary symptoms. His only medical history was a ureteric stone. He did not take any drugs, and drunk alcohol in moderate amounts regularly.

On examination he seemed well, apyrexial but tachycardic with a pulse rate of 110 beats per minute. His blood pressure was normal. His chest was clear. Examination of his abdomen showed a tender 15×10 cm swelling in the right anterior lumbar region.

Chest radiograph did not show pneumoperitoneum. His blood test showed neutrophilia (20×10⁹/l and a raised C reactive protein of 200 mg/l. The rest of the blood tests including amylase were in the normal range. An abdominal radiograph and computed tomogram of the abdomen and pelvis were performed.⇓