Air in the main pancreatic duct: demonstration with US.

Air in the pancreas--nearly always related to an abscess or a pancreatic fistula--is rarely demonstrated. Over a 3-year period, the authors detected air in the main pancreatic duct with ultrasonography (US) in 11 patients. The ductal caliber was normal in five patients and dilated in six. At US, air in the main pancreatic duct is characterized by strongly echogenic foci or echogenic lines in the duct, casting acoustic shadows or producing reverberation artifacts. It is likely that in patients who have biliary-enteric anastomoses or have undergone sphincterotomy, air in the duct of Wirsung is the result of biliary-pancreatic reflux. In patients who have not undergone such operations, the likely cause of pancreatic gas is duodenal-pancreatic duct reflux. Pancreatic gas may be related to causes other than a pancreatic abscess or fistula; it is therefore important for clinicians to realize that pancreatic ductal gas seen on US images may be secondary to prior surgery or due to sphincter of Oddi dysfunction.