Portal Vein and Hepatic Vasculature Doppler: A Practical Guide

Hepatic vascular Doppler is a critical component of liver disease evaluation, transplant surveillance, and portal hypertension workup. Understanding the normal waveform patterns and what changes mean is essential for any sonographer scanning abdominal studies.

Vessels to Evaluate

1. Portal vein — main, right, and left branches
2. Hepatic veins — right, middle, left (drain into IVC)
3. Hepatic artery — proper hepatic → right and left branches
4. IVC — at the hepatic vein confluence

Normal Portal Vein

Anatomy: The portal vein forms at the confluence of the superior mesenteric vein (SMV) and splenic vein behind the pancreatic neck. It runs in the porta hepatis with the hepatic artery and common bile duct (portal triad).

Normal values:

Parameter	Normal
Portal vein diameter	< 13 mm (at porta hepatis, held at end-expiration)
Flow direction	Hepatopetal (toward the liver)
Velocity	15–40 cm/s
Waveform	Mildly phasic (varies with respiration and cardiac cycle)

How to measure diameter: Transverse plane at the porta hepatis, measured from inner wall to inner wall, during quiet end-expiration. Inspiration causes it to dilate — don't measure during a deep breath.

Waveform character: The portal vein shows a gently undulating, continuous hepatopetal flow. It does not have the sharp peaks of the hepatic artery or the phasic waveform of the hepatic veins.

Portal Hypertension Findings

Portal hypertension (PHT) — elevated pressure in the portal system — causes characteristic changes visible on Doppler.

Findings in PHT:

• Dilated portal vein (> 13 mm)
• Reduced portal vein velocity (< 15 cm/s)
• Loss of respiratory phasicity — velocity becomes flat and monotonic
• Hepatofugal flow — reversed portal vein flow (away from the liver) — indicates severe PHT
• Varices — dilated tortuous vessels at the splenic and gastroesophageal regions
• Splenomegaly
• Ascites
• Collaterals — recanalized paraumbilical vein, splenorenal collaterals, gastric varices

Congestion index (CI): Portal vein cross-sectional area ÷ mean velocity. CI > 0.1 cm·s suggests significant PHT. Rarely used in routine practice but worth knowing.

Hepatic Veins

The three hepatic veins (right, middle, left) drain into the IVC at the superior liver margin.

Normal waveform: Triphasic — reflects right atrial pressure changes:

• S wave (systolic hepatic vein flow)
• D wave (diastolic flow)
• A wave reversal (atrial contraction)

This triphasic waveform looks like a "W" or "M" pattern and is the normal appearance of hepatic vein Doppler.

Abnormal patterns:

Pattern	Appearance	Significance
Biphasic	S and D waves, no A reversal	Mild change, early congestion
Monophasic/flat	Continuous non-phasic flow	Significant hepatic fibrosis, cirrhosis, Budd-Chiari
Reversed/hepatofugal	Flow away from IVC	Severe congestion, Budd-Chiari

Budd-Chiari syndrome: Thrombosis of the hepatic veins or suprahepatic IVC. Look for absent flow in hepatic veins, reversed or absent IVC flow, hepatomegaly, and caudate lobe hypertrophy (caudate has separate venous drainage and enlarges when other hepatic veins are occluded).

Hepatic Artery

The hepatic artery runs in the portal triad — the same echogenic band as the portal vein and bile duct at the porta hepatis.

Normal values:

Parameter	Normal
PSV	50–150 cm/s
RI (resistive index)	0.55–0.75
Waveform	Low-resistance: brisk systolic upstroke, continuous forward diastolic flow

The hepatic artery should always have forward diastolic flow — it supplies a metabolically active organ. Absent or reversed diastolic flow is abnormal.

Resistive index (RI): (PSV − EDV) ÷ PSV

• RI < 0.55: May suggest AV fistula or arterioportal shunt
• RI > 0.80: Hepatic artery thrombosis (HAT), severe hepatitis, rejection (in transplants), acute obstruction

Liver Transplant Surveillance

Hepatic Doppler is the primary monitoring tool after liver transplantation. The anastomosis of the hepatic artery is technically demanding and HAT is the most feared early complication.

What to assess post-transplant:

• Hepatic artery: PSV, RI, waveform — must have forward diastolic flow
• Portal vein: direction, velocity, anastomotic stenosis
• Hepatic veins: phasicity, outflow obstruction
• IVC: patency at anastomoses

Hepatic artery thrombosis (HAT):

• Absent hepatic artery flow in the liver — urgent finding
• Can lead to biliary ischemia and graft loss
• RI suddenly elevated or absent diastolic flow may precede complete occlusion

Hepatic artery stenosis:

• PSV > 300 cm/s at anastomosis, or PSV ratio > 3:1 across anastomosis
• Tardus-parvus waveforms distally (slow systolic upstroke, RI < 0.5)

Portal vein stenosis:

• PSV > 100–125 cm/s at anastomosis, or > 3:1 ratio across it
• May cause portal hypertension in the graft

Key Images to Capture

1. Portal vein — B-mode with measurement (diameter)
2. Portal vein — color Doppler showing direction
3. Portal vein — spectral waveform with velocity
4. Main hepatic artery — spectral with PSV, EDV, RI
5. Each hepatic vein — spectral waveform
6. IVC at hepatic vein confluence

Reporting Language

• "Patent portal vein with hepatopetal flow, velocity 22 cm/s, diameter 10 mm. Hepatic artery RI 0.62, normal low-resistance waveform. Hepatic veins with normal triphasic waveforms."
• "Dilated portal vein measuring 16 mm. Markedly reduced portal vein velocity at 8 cm/s. Hepatofugal flow identified in the left portal vein. Findings consistent with portal hypertension. Splenomegaly and small volume ascites noted."
• "Post liver transplant: Hepatic artery present with RI 0.58 and forward diastolic flow. No tardus-parvus waveforms. Portal vein patent, hepatopetal, velocity 28 cm/s. Hepatic vein outflow patent."

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SonoBuddy's Measurements section includes portal vein diameter, hepatic artery RI, and hepatic vein waveform reference values.