Portal venous gas

Always abnormal
Present when intestinal permeability increases or when there is increase in intestinal luminal pressure
Neonatal necrotising enterocolitis, adults with gastric emphysema, intestinal obstruction, infection, Crohn disease
Blunt abdominal trauma, invasive malignancies (colon, ovarian carcinoma)
Duodenal perforation at ERCP
Colitis following barium enema
Gas radiates out of hilum
Less gravity dependence than pneumobilia, more peripheral distribution

US: moving gas bubbles in portal vein. Aliasing artifacts on spectral display.
CT and radiograph: evident when enough gas accumulates and is seen in periphery of liver