In the splenic flexure (at the site of annular constricting mass on CT scan performed 6 months previously - arrow) there is a large mass containing gas (arrow) consistent with a perforated colonic neoplasm and abscess. Interestingly there is no associated large bowel obstruction. Gas is also present within the muscle fibres of the left groin and lateral pelvic wall (arrow). This is not obviously in direct communication with the splenic flexure lesion thus may represent haematogenous spread of infection by gas-forming organisms