Portal venous gas refers to the presence of gas (air) within the portal venous system of the liver. It appears on ultrasound as tiny, bright, hyperechoic foci that move with blood flow toward the periphery of the liver (unlike pneumobilia, or air in the bile ducts, which tends to be central). This finding can be dramatic, with echogenic specks seen streaming through the portal vein branches. Portal venous gas may be caused by bowel ischemia or infarction (the most serious cause), bowel obstruction, inflammatory bowel disease, recent abdominal surgery, or endoscopic procedures. While it was historically considered an ominous finding requiring emergency surgery, the clinical significance depends on the underlying cause, and some benign causes are increasingly recognized.