Image challenge: Profound diarrhea after cholecystectomy

Gastroenterology clinical image challenge: A 73-year-old man was referred for evaluation of daily diarrhea of six weeks duration. He denied constipation but did report scant red blood per rectum and a 10-pound weight loss. The passage of liquid stool promptly after eating has rendered the patient homebound. Multiple comorbid conditions were present, including diabetes mellitus type 2, hypertension and chronic kidney disease (stage III). Approximately four months previously, an attempted laparoscopic cholecystectomy was converted to open after the development of massive hemorrhage after a vascular injury in the area of the gallbladder fossa. Pathologic examination of the gallbladder revealed chronic cholecystitis. Physical examination was unremarkable. Stool for occult blood and Clostridium difficile toxin were negative, no pathogens were cultured, and no parasites demonstrated. Laboratory studies were notable for a hemoglobin of 11.1 g/dL, blood urea nitrogen of 56 mg/dL and creatinine of 1.6 mg/dL. A computed tomography scan of the abdomen and pelvis demonstrated changes of prior cholecystectomy. The ascending colon extended into the gallbladder fossa and seemed to be apposed to the duodenum. Colonoscopy demonstrated diverticulosis coli throughout the colon with no inflammatory changes. At approximately the hepatic flexure a large mouth orifice was encountered that appeared different from the other diverticulae. Random colon biopsies were unremarkable. On upper endoscopy, there was a similar opening on the floor of the duodenal bulb (Figure) through which tissue consistent with colonic mucosa could be observed.

Gastrointestinal radiography demonstrated simultaneous visualization of the duodenum and the hepatic flexure spilling into the proximal colon (Figure). Compression views captured a flow of contrast from the duodenal bulb into the hepatic flexure (Figure).

What is the diagnosis?