Summary

A 69-year-old man was admitted with non-resolving right leg cellulitis. Subsequent skin changes over the calf and discharging pus suggested necrotising fasciitis. After several wound debridements of the leg and imaging, the patient was found to have an iliopsoas abscess due to a metastatic perforated caecal tumour extending along the medial thigh to the calf. No micro-organisms indicative of typical necrotising fasciitis were isolated from the wound. The patient had an ileocaecal resection, and his leg was reconstructed with a split thickness skin graft. He continues to do well postoperatively. This case highlights key lessons when dealing with an unusual presentation leading to challenges in diagnosis such as: (1) the need for good interspecialty liaison, (2) prompt senior review and plan, and (3) ‘thinking outside the box’ when faced with a diagnostic challenge.