Gas-forming abdominal wall abscess: unusual manifestation of perforated retroperitoneal appendicitis extending through the superior lumbar triangle

We present a case of an extensive gas-forming abdominal wall abscess secondary to ruptured retroperitoneal appendicitis in a diabetic patient. Computed tomography (CT) demonstrated a retroperitoneal abscess extending to the abdominal subcutaneous tissue through the superior lumbar triangle pathway, a known anatomical defect of the lumbar musculature. This case not only represents an unusual manifestation of acute appendicitis, but also alerts us to the importance of anatomical considerations in the imaging interpretation of disease extent. The applied anatomy of the lumbar triangle as a conduit of intra-abdominal and retroperitoneal processes into the abdominal wall is reviewed.