The patient was hospitalized 3 months ago for acute pancreatitis combined with a choledochal cyst, and I placed an ENBD drain in him. The patient complained that the discomfort in the right upper abdomen had completely disappeared except for a slight tugging sensation and numbness at the incision. The patient’s ultrasound report showed that the liver was basically normal, but there was pneumatization of the intrahepatic bile duct. The patient was more concerned about this description and asked me to explain it, and I will explain this situation of bile duct pneumatization below. Figure 1: A case of intrahepatic pneumatization in a patient with a postoperative common bile duct cyst. In normal people, the biliary sphincter exists in the duodenal papilla and acts as a one-way valve, which means that bile can drain into the intestine, but gas in the intestine cannot return to the bile duct. In this patient, since the bile duct cyst was removed and a bile-intestinal anastomosis was performed, there is no biliary sphincter, so since bile can flow into the intestinal duct, gas in the intestinal duct can freely enter and exit the intrahepatic bile duct, thus causing gas accumulation in the bile duct. This is a normal postoperative change, and as long as there is no inflammation, there is no need to worry. Also, patients who have undergone ERCP lithotripsy can also experience postoperative pneumatization of the biliary tract due to duodenal papillotomy. Some patients may ask, since intestinal gas can enter and exit the bile duct freely, will the food eaten also enter and exit the bile duct freely thus causing reflux cholangitis? This is a good question. It turns out that we have designed an anti-reflux “device” in the bile-intestinal anastomosis: a section of about 40 cm of drainage collaterals connecting the bile duct and the normal intestine. The normal intestine is also in the normal intestine. Figure 2: A biliary-intestinal anastomosis with intestinal collaterals1 to help combat food reflux. Of course, if a patient has gas accumulation in the bile duct even without surgery, it is likely that the lower biliary sphincter is impaired due to stones, biliary ascaris, and other factors that do not effectively prevent retrograde transmission of intestinal gas.