A 72-year-old woman presents with 2 days of colicky central abdominal pain, distension and vomiting. She is afebrile. Abdominal radiograph shows dilated small bowel loops, gas in the biliary tree, and a faintly calcified opacity in the right iliac fossa distinct from the gallbladder region. The most likely diagnosis is:

• A Adhesive small bowel obstruction
• B Carcinoma of the caecum causing obstruction
• C Gallstone ileus from a cholecystoduodenal fistula ✓
• D Intussusception secondary to a Meckel's diverticulum

Explanation

The combination of small bowel obstruction, pneumobilia and an ectopic calcified stone constitutes Rigler's triad, which is diagnostic of gallstone ileus. A large stone erodes through the gallbladder into the duodenum, the most common site of fistula formation, and impacts at the narrow terminal ileum. Adhesions would explain obstruction but not pneumobilia, and caecal carcinoma would give a large bowel pattern.

Reference: Bailey and Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.