The most common ultrasound changes in cirrhosis are a nodular appearance on the surface, heterogeneous echotexture, relative enlargement of the caudate lobe compared to the right lobe, and atrophy of the medial segment of the left lobe. The most common etiologies of cirrhosis are alcohol, followed by viral hepatitis, cryptogenic infection, vascular pathologies, and metabolic disorders. Congestive right heart failure also can cause painless, diffuse wall thickening of the gallbladder. Changes in the hepatic vein and IVC velocity pattern can be appreciated in color Doppler ultrasound with loss of normal triphasic flow and flattening of the waveform in hepatic veins.

Ultrasound manifestations of passive hepatic congestion are right hepatic lobe enlargement, inferior vena cava dilatation, and hepatic vein enlargement. It is due to hepatic venous drainage impairment and stasis of blood in hepatic parenchyma. Cardiac disease, including congestive heart failure, restrictive cardiomyopathy, and right-sided valvular disease, can cause hepatomegaly and dilation of hepatic veins, called passive hepatic congestion. Hepatomegaly and liver cirrhosis are two main pathologies that distort the liver anatomy. Portal hypertension can be appreciated in CT and MRI with similar manifestations on ultrasound and the presence of contrast in the paraumbilical vein, which is pathognomonic. Ultrasound manifestations of portal hypertension are a dilated portal vein (>13 mm), a dilation of the splenic and superior mesenteric veins, the presence of collateral vessels between the portal and systemic pathways, splenomegaly, ascites, and the presence of biphasic or reversed flow (hepatofugal flow) on Doppler US which is diagnostic and pathognomonic for portal hypertension. Different pathologies can cause portal hypertension, including portal vein thrombosis, cirrhosis, viral hepatitis, Budd-Chiari syndrome, and congestive heart failure. Portal hypertension or hepatic venous pressure gradient is defined as a portosystemic pressure gradient. Although the portal vein provides 75% of the liver's blood supply, it provides 50% of its oxygen supply. It divides into the right hepatic vein and porta hepatis. Inferior mesenteric, gastric, and cystic veins drain into the portal vein. The portal vein forms from the junction of the superior mesenteric artery and splenic veins behind the neck of the pancreas. The portal triad, which includes the portal veins, hepatic arteries, and bile ducts surrounded by fibrofatty tissue, can be seen as echogenic foci throughout the liver.

The hepatic veins enter the inferior vena cava and can be seen as anechoic tubes with thin walls on ultrasound. Arterial embolization and treatment targets tumors rather than normal hepatic cells. Tumors that get supply from the hepatic artery will enhance during the arterial phase, which is the principle in transarterial chemoembolization and chemoembolization. The hepatic blood supply is from the portal vein (about two-thirds), and the rest is from the hepatic artery thus, maximum enhancement of the liver is attained during the portal venous phase, which is 60 to 120 seconds after arterial phase enhancement. Segments V, VI, VII, and VIII constitute the right lobe hepatic sections. Segment II, III, and IV are left hepatic lobe sections. Segment I is the caudate lobe, which is unique and can receive dual blood supply from the right and left portal vein and drains directly into IVC. The portal vein divides segments horizontally into the superior and inferior segments. The right hepatic vein divides the right lobe into the anterior and posterior segments, and the falciform ligament divides the left lobe into medial and lateral segments. The middle hepatic vein runs from the inferior vena cava to the gallbladder fossa and divides the liver into the right and left lobes. The hepatic vein runs between two adjacent segments and drains into the inferior vena cava (IVC). A single branch of the hepatic artery, portal vein, and bile duct enters through the apex into the hepatic segments. Each segment is wedge-shaped, with the apex directed towards the hepatic hilum with some variability. The most widely used anatomic classification of hepatic segments is Couinaud classification which describes eight functionally independent liver segments based on vascularization, bile duct distribution, and lymphatic drainage.

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