The patient was taken to the operating room for exploration. A 3-mm fistulous tract was identified on the hepatic flexure of the colonic lumen (Fig. D). A segment of the transverse colon was resected, and cholecystectomy was performed. On pathological examination, the mucosa of the colon was focally necrotic. Meanwhile, a 2.5-cm fistula was connected to the gallbladder, and a calcium bilirubinate stone was found in the fistula (Fig. E, arrows; H&E, ×100). These findings were consistent with a diagnosis of cholecystocolic fistula.

Biliary-enteric fistulas have been found in 0.9% of patients undergoing biliary tract surgery.¹ The most common site was the cholecystoduodenal fistula (70%), followed by cholecystocolic fistula (10%-20%).¹ Diarrhea was the most common and valuable distinguishing symptom of cholecystocolic fistula.² Other symptoms of abdominal pain, cholangitis, weight loss, and bowel obstruction were reported.^2,3 Lower gastrointestinal bleeding was a rare presentation. The intermittent bleeding occurred from the stone necrosis of the gallbladder wall contiguous with the inflamed colon, and the migrating stone in the fistula could erode and seal off the bleeding vessels. Awareness of symptoms coupled with colonoscopic examination, barium enema, or biliary scintigraphy is required to make a preoperative diagnosis.