What distinguishes portal venous gas from septic pneumobilia?
Although in both conditions gas is in a branching, tapering pattern, the location within the liver of the gas is usually distinctive. Because portal venous blood normally flows toward the periphery, gas in portal veins tends to accumulate in the periphery of the liver. Because bile normally flows toward the hilum, biliary gas tends to accumulate near the hilum. These rules occasionally fail, however, because at the instant the radiograph is exposed the location of the constantly moving gas may transiently be atypical. Diligent inspection of the radiograph for secondary signs such as pneumatosis intestinalis is helpful because, if present, it is indicative of bowel ischemia and indicates the intrahepatic gas is within the portal system.
Pneumobilia is most commonly seen due to ampullary sphicterotomy or choledocoenterotomy. This is a benign finding. Pneumobilia caused by bacterial gas production within the biliary tree is uncommon and the patient is usually septic. It is imperative that the radiologist be provided with clinical information to make this distinction.