Can you tell the difference between hepatic portal and biliary gas?

Multiphase Multidetector-Row CT Reveals Different Patterns of Hepatic Portal Venous Gas and Pneumobilia

Alessia Cordella, Giovanna Bertolini

Background
Hepatic portal venous gas (HPVG) and pneumobilia (PB) are rare but clinically significant findings indicating the presence of gas within the portal venous system or biliary tree, respectively. In human medicine, CT is the preferred imaging modality to differentiate these conditions, but limited information exists in veterinary medicine. This study aimed to describe the CT features of HPVG and PB in dogs and cats and determine imaging characteristics that aid in differentiation.

Methods
A retrospective analysis was conducted on patients diagnosed with HPVG or PB via multiphase multidetector-row CT at a veterinary diagnostic center. The study included five cases (four dogs, one cat) with confirmed intrahepatic gas. CT images were evaluated using thin-section multiplanar reformatting and minimum intensity projection (MinIP) techniques. Recorded CT features included the location, shape, and distribution of gas within the liver.

Results
Two patients had HPVG, and three had PB. HPVG was characterized by a tubular gas pattern in the periphery of the liver, extending near the hepatic capsule. PB, in contrast, appeared as a mixed tubular and rounded gas pattern in the central liver, typically near the porta hepatis. The severity and distribution of gas varied among cases, but no clear difference was found in the amount of gas present between the two conditions. MinIP imaging improved the visualization of intrahepatic gas, particularly in cases with small gas volumes. The underlying causes of HPVG included gastrointestinal disease and intestinal pneumatosis, while PB was primarily associated with previous hepatobiliary surgery or emphysematous cholecystitis.

Limitations
The study included only five cases, limiting statistical power. Retrospective design and potential selection bias may affect generalizability. Additionally, pathological confirmation of underlying diseases was not available in all cases.

Conclusions
Multiphase CT successfully differentiates HPVG from PB based on gas location and morphology. HPVG presents as peripheral, tubular gas, while PB appears centrally with a mixed morphology. These findings emphasize the importance of advanced imaging techniques, particularly MinIP, in accurately diagnosing intrahepatic gas and guiding clinical management.

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