Gas within portal venous system

Grayscale ultrasound

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  Highly reflective foci in portal venous system

  
  
  
  
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    Move along with blood

  
  
  
  
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  Poorly defined, highly reflective parenchymal foci

  
  
  
  
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    Scattered small patches to numerous or large areas

  
  

Pulsed Doppler ultrasound

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  High-intensity transient signals (HITS)

  
  
  
  
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    Strong transient spikes superimposed on portal venous flow pattern

  
  

Color Doppler ultrasound

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  Bright reflectors in portal venous system

Biliary tract gas

Parenchymal abscess

Biliary calculi/parenchymal calcifications

Hepatic artery calcification

Sources of gas: Gas under pressure, intravasation from mucosa, gas-forming organism

Serious conditions

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  Necrotizing enterocolitis, bowel ischemia/infarction

Benign conditions

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  Bowel distension, intervention-related, benign pneumatosis intestinalis

Often sign of serious condition; but can sometimes be inconsequential finding

Rule out other conditions mimicking portal venous gas

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  Biliary tract gas, biliary calculi, or hepatic calcification

Best imaging clue: Bright reflectors in portal veins on grayscale or color Doppler

To distinguish rouleaux formation in slow-flow veins from gas bubbles, use spectral tracings, which will detect HITs that correspond to gas

With B-flow imaging, portal venous gas may be more clearly delineated