Cholecystoduodenal fistula with gastric outlet obstruction

A 68-year-old man with a history of a gallbladder stone for many years suffered acute right upper quadrant pain and was admitted to the emergency room. Computed tomography of the abdomen showed a very high-density shadow in the gallbladder (Fig. 1A). His symptoms were relieved after receiving antibiotics and spasmolytic treatment, but he refused to accept further cholecystectomy. Five months later, the patient presented with a 2-week history of postprandial nausea and vomiting. Physical examination found abdominal splashing sound. Computed tomography revealed a large dense shadow in the duodenum, while the gallbladder appeared atrophic with pneumatosis (Fig. 1B). What could the patient’s diagnosis be?