Doppler of the Portal Vein: Norms and Signs of Portal Hypertension

Normal Doppler Parameters of the Portal Vein

Blood flow in the portal vein is normally hepatopetal (directed towards the liver), relatively continuous, with low velocities that slightly vary with respiration. The normal waveform is hepatopetal and mildly phasic (gentle undulation). According to sources, normal velocity values are 12–24 cm/s via intercostal (transcostal) access with an average resistive index of 0.36; portal venous flow >16 cm/s is considered normal. A range of low velocities from 16–40 cm/s is also cited as normal.

Normally, blood flow in the superior mesenteric and splenic veins is also hepatopetal (directed towards the liver).

Technical Requirements for the Examination

The examination is performed using both B-mode and Doppler assessment of the portal system, hepatic veins, and hepatic arteries. The transducer should be parallel to the vessel; the Doppler angle should be less than 60 degrees to obtain the maximum peak systolic velocity. In suspected portal hypertension, Doppler with angle correction should be applied not only to the main portal vein but also to the right and left intrahepatic branches, as hepatofugal flow may affect only one of them.

Signs of Portal Hypertension

Key Doppler and secondary signs:

• Low peak systolic velocity of portal flow — drop below 20 cm/s.
• Pulsatility of the portal vein — a highly sensitive sign, manifests as a to-and-fro pattern (low amplitude flow above and below the baseline).
• Hepatofugal (reversed) flow.
• Detection of collateral vessels (portosystemic collaterals).
• Enlargement of the portal vein diameter >12.5 mm indicates cirrhosis (sensitivity and specificity about 80%). As portosystemic shunts develop, the diameter of the portal vein decreases.

An increase in the arterioportal peak velocity ratio (maximum hepatic artery velocity / maximum portal vein velocity) greater than 3.5 is predictive of cirrhosis. The positive predictive value for detecting portal hypertension is excellent, with signs including reversed portal flow and collaterals; the negative predictive value is lower, with an overall accuracy of only 60%.

Hepatic Veins in Cirrhosis

In compensated cirrhosis (without portal hypertension), the Doppler waveform of the hepatic veins becomes abnormal: the amplitude of phasic oscillations decreases, the reversed component is lost, and the waveform flattens. As cirrhosis progresses, the hepatic veins develop lumen narrowing with increased velocities and flow turbulence.

Secondary Signs and Differential Diagnosis

Splenomegaly, changes in liver size, ascites, and portosystemic venous collaterals should be assessed. A pulsatile portal vein (large difference between peak systolic and end-diastolic velocities) may occur with tricuspid regurgitation and right ventricular heart failure. In portal vein thrombosis, a direct sign is the visualization of a thrombus; indirect signs include the loss of normal portal landmarks, dilation of the superior mesenteric and splenic veins.