Cholecysto-duodenal fistulas are not frequent and usually result from cholelithiasis.' Another cause of cholecysto-duodenal fistula, accounting for only 5% of cases, is a penetrating duodenal ulcer.2We present the sonographic and computed tomography (CT) findings of a cholecysto-duodenal fistula due to the perforation of a duodenal ulcer into the gallbladder. CASE REPORTA 49-year-old man was referred to our institution for further investigation of acute vomiting following a 3-month history of progressive right upper quadrant pain. He had been treated conservatively for a duodenal ulcer 5 years prior to his present admission. Physical examination revealed tenderness of the right upper quadrant. He had no fever and a normal white blood count; other routine laboratory tests were normal. Conventional x-rays of the abdomen were read as normal.Abdominal sonography revealed a n undistended gallbladder without wall thickening, stones, or pericholecystic fluid. Highly reflective echoes were seen in the upper part of the gallbladder lumen ( Figure 1A). These reflective echoes were associated with reverberation shadows (Figure lB), and moved along the gallbladder wall with changes in the patient's position, corresponding to gas in the gallbladder lumen. The gallbladder was in close contact with the first part of the duodenum, which presented as a thick- 506ened wall. Sonography showed no air in the biliary tract. A tiny hyperechoic spot with reverberation artefact was detected on the medial surface of the right lobe of the liver, between the gallbladder and the right colonic flexure (Figure 10, suggesting a localized pneumoperitoneum. The absence of clinical and sonographic signs of cholecystitis and the previous history of duodenal ulcer made us consider that gas in the gallbladder was secondary to a penetrating duodenal ulcer.An abdominal CT study performed to assess the sonographic suspicion of a localized pneumoperitoneum revealed diverticuli of the hepatic flexure of the colon and no pneumoperitoneum. CT examination confirmed the presence of gas within the gallbladder lumen, with no sign of inflammation (Figures 2A and B). There was no fat plane between the gallbladder and the second part of the duodenum. These findings were interpreted as a duodeno-cholecystic fistula. The endoscopic examination, performed on the same day, demonstrated an acute penetrating ulcer of the proximal portion of the duodenum. As there was no perforation into the peritoneal cavity, the patient was not operated on and improved within a few days under medical treatment. A CT study performed 1 month later showed a normal gallbladder. The patient had no recurrent pain during a 6-month follow-up period. DISCUSSIONGas in the gallbladder lumen may be secondary to emphysematous cholecystitis, biliary enteric fistula, anastomosis, or endoscopic procedures. Biliary enteric fistulas are uncommon findings, representing 0.9% of nonmalignant biliary tract diseases. The majority of these fistulas are chole- JOURNAL OF CLINICAL ULTRASOUND