Appendicitis probably results from an obstruction of the intestinal lumen caused by a fecal mass, stricture, barium ingestion, or viral infection. This obstruction sets off an inflammatory process that can lead to infection, thrombosis, necrosis, and perforation. If the appendix ruptures or perforates, the infected contents spill into the abdominal cavity, causing peritonitis, the most common and most perilous complication of appendicitis.

Appendicitis usually begins with generalized or localized colicky periumbilical or epigastric pain, followed by anorexia, nausea, and a few episodes of vomiting. Pain eventually localizes in the right lower quadrant of the abdomen (McBurney’s point), with abdominal “boardlike” rigidity, retractive respirations, increasing tenderness, increasingly severe abdominal spasms and, almost invariably, rebound tenderness. (Rebound tenderness on the opposite side of the abdomen suggests peritoneal inflammation.)