What is portal venous gas on CT and what does its presence signify?

• A. Gas within portal venous system; suggests bowel ischemia, infarction, or severe infection; urgent evaluation.
• B. Gas within the biliary tree; cholangitis.
• C. Gas in stomach; perforation.
• D. Gas in bowel lumen; normal.

Answer: (A)

Portal venous gas on CT means gas is found within the portal venous system. Its presence is a red flag because it most often signals bowel ischemia or infarction, and can accompany severe infection. Gas from the bowel lumen can breach the mucosa and enter mesenteric veins, traveling to the portal system and then the liver, which is why this finding carries a high risk of necrosis and sepsis. On CT, portal venous gas appears as branching lucencies in the liver that extend toward the liver capsule, typically more peripheral. This distribution helps distinguish it from gas in the biliary tree (pneumobilia), which tends to be central near the hilum. Because portal venous gas is associated with serious intra-abdominal pathology, urgent evaluation and often surgical consultation are required. Gas in the biliary tree is due to different processes (like prior biliary procedures) and gas in the stomach or bowel lumen can be normal or indicate perforation depending on context, so they do not represent portal venous gas.