Section 4.1: Hepatocellular Disease, Fatty Infiltration, and Cirrhosis

Section 4.1: Hepatocellular Disease, Fatty Infiltration, and Cirrhosis

Pathophysiology of Hepatocellular Disease and Laboratory Diagnostics

Hepatocellular disease is characterized by diffuse damage to the functional cells of the liver (hepatocytes). Unlike focal lesions, hepatocellular processes alter the entire liver parenchyma, which in turn alters its overall echogenicity, attenuation, and vascular flow dynamics. On the ARDMS Abdomen exam, correlating sonographic patterns with laboratory values is essential. Acute damage to hepatocytes leads to the leakage of intracellular enzymes into the bloodstream. Alanine aminotransferase (ALT) is highly specific to the liver, whereas aspartate aminotransferase (AST) is present in other metabolically active tissues (heart, muscle). In acute hepatitis or toxic liver injury, AST and ALT rise dramatically, often exceeding ten times the upper limit of normal. Conversely, chronic diseases like cirrhosis may present with normal or only mildly elevated transaminases. Other key labs include serum albumin (which decreases in liver failure due to impaired synthesis), bilirubin (conjugated bilirubin rises with biliary obstruction, while unconjugated bilirubin rises with hepatocellular dysfunction or hemolysis), and prothrombin time (PT), which prolongs as the liver fails to synthesize vitamin K-dependent clotting factors.

Hepatitis: Acute versus Chronic

Hepatitis represents inflammatory cellular infiltration of the liver parenchyma, most commonly viral (Hepatitis A, B, C, D, or E) but also chemical, drug-induced, or autoimmune.

• Acute Hepatitis: Sonographically, acute hepatitis is marked by a diffuse decrease in parenchymal echogenicity. This hypoechoic tissue provides an acoustic contrast that makes the walls of the portal venules appear abnormally bright. This phenomenon is known as the "starry sky" or "periportal cuffing" appearance. Associated signs include hepatomegaly (sagittal liver length > 15–15.5 cm at the midclavicular line), diffuse gallbladder wall thickening (> 3 mm) without cholelithiasis, and localized lymphadenopathy at the porta hepatis. The decrease in liver echogenicity occurs because intracellular edema scatters sound waves less effectively.
• Chronic Hepatitis: Defined by clinical or biopsy evidence of hepatic inflammation persisting for more than six months. Chronic hepatitis leads to progressive fibrosis. Sonographically, the liver demonstrates a diffuse increase in echogenicity and a coarser parenchymal echotexture. The increased fat and fibrous tissue attenuate the sound beam, reducing the visualization of deep portal vein walls (loss of the starry sky contrast). Unlike acute hepatitis, chronic hepatitis causes the liver to decrease in size as it progresses, leading to atrophy of the lobes and a nodular or irregular surface outline.

Fatty Infiltration (Hepatic Steatosis)

Hepatic steatosis is the abnormal accumulation of intracellular triglycerides within hepatocytes. It is a reversible condition caused by alcohol abuse, obesity, diabetes mellitus, hyperlipidemia, severe hepatitis, or glycogen storage disease. Sonographically, fatty liver is categorized into three distinct grades based on the degree of sound attenuation and visualization of deep structures:

• Grade I (Mild): Diffuse, mild increase in hepatic echogenicity. The diaphragm and intrahepatic vessels are clearly visualized.
• Grade II (Moderate): Moderate increase in echogenicity. The visualization of the diaphragm and portal vessels is slightly impaired due to acoustic attenuation.
• Grade III (Severe): Marked increase in echogenicity. There is severe posterior acoustic attenuation, making it extremely difficult or impossible to visualize the diaphragm, deep hepatic vessels, and posterior aspect of the right lobe.

Focal Infiltration and Focal Sparing

Fatty infiltration is not always uniform. The registry frequently tests the two focal variants:

1. Focal Fatty Infiltration: Regions of increased echogenicity within an otherwise normal liver. This typically presents as a geographic, non-mass-like echogenic region. Crucially, it does not exert mass effect (no displacement of adjacent vessels or distortion of the liver capsule). It commonly occurs near the porta hepatis, adjacent to the gallbladder, or along the liver margins.
2. Focal Fatty Sparing: Hypoechoic regions within a diffusely echogenic, fatty liver. These spared zones are most commonly located anterior to the bifurcation of the main portal vein, in the gallbladder bed, or in the caudate lobe. They represent normal liver parenchyma that has been spared from lipid accumulation. Like focal infiltration, focal sparing does not exert mass effect, and normal portal vessels course straight through the region without deviation.

Sonographic Presentation of Cirrhosis

Cirrhosis is the end stage of chronic liver injury, characterized by diffuse parenchymal necrosis, fibrous tissue deposition, and nodular regeneration. The most common etiologies are alcohol abuse and chronic Hepatitis C. The sonographic signs of cirrhosis are distinct and form a high-yield portion of the exam:

• Nodular Liver Surface: The most sensitive and specific sign. It is best evaluated using a high-frequency linear transducer (7.5–12 MHz) placed over the anterior surface of the left or right lobe. The presence of ascites enhances the visualization of these surface irregularities by acting as a fluid acoustic window.
• Coarse, Heterogeneous Echotexture: The parenchyma loses its normal homogeneous, fine-level echo pattern and appears coarse and patchy, reflecting the nodular regeneration and dense fibrous bands.
• Lobe Size Disproportions (Caudate Lobe Hypertrophy): Cirrhosis causes atrophy of the right lobe and the medial segment of the left lobe, while the caudate lobe and lateral segment of the left lobe undergo compensatory hypertrophy. The caudate lobe is spared because it has a separate venous drainage directly into the inferior vena cava (IVC) via short hepatic veins, shielding it from portal hypertension-induced congestion. A caudate lobe-to-right lobe (C/RL) ratio of 0.65 or greater is highly specific for cirrhosis.
• Ascites: Transudative fluid accumulation in the peritoneal spaces, including Morison's pouch, the subphrenic spaces, and the paracolic gutters.

Portal Hypertension, Collateral Pathways, and Shunts

Portal hypertension is defined as an increase in portal venous pressure exceeding 10–12 mmHg, caused by increased resistance to portal blood flow (most commonly sinusoidal obstruction due to cirrhosis). The clinical sequelae and sonographic manifestations are profound:

• Portal Vein Dilation: The main portal vein diameter increases beyond 13 mm (measured where it crosses anterior to the IVC during quiet respiration).
• Splenomegaly: Enlargement of the spleen, with a longitudinal length exceeding 13 cm. Splenic congestion is a direct result of backpressure.
• Loss of Respiratory Variation: Normal portal and splenic veins demonstrate mild respiratory variation in caliber; this is lost in portal hypertension.
• Portosystemic Collaterals (Varices): The body attempts to decompress the portal system by opening embryonic vascular pathways. The most critical collaterals tested are:
  • Recanalized Umbilical Vein: The ligamentum teres patency is re-established. It appears as an anechoic channel (> 3 mm) arising from the left portal vein and coursing anteriorly through the falciform ligament toward the umbilicus. Doppler demonstrates hepatofugal flow.
  • Coronary (Left Gastric) Vein: Connects the portal vein to the esophageal veins. It is considered dilated when it exceeds 5 mm, carrying hepatofugal flow.
  • Splenorenal Collaterals: Tortuous varices between the splenic hilum and the left renal vein.
• Doppler Hemodynamics: Flow in the main portal vein slows, loses its normal gentle respiratory undulations, and becomes monophasic. As pressure increases, flow may become biphasic (alternating hepatopetal and hepatofugal) and ultimately hepatofugal (completely reversed, away from the liver).
• TIPS Evaluation: Transjugular Intrahepatic Portosystemic Shunts are placed between a hepatic vein (usually right) and a portal vein branch (usually right) to decompress the portal system. Normal TIPS velocities range from 50 to 190 cm/s. Shunt dysfunction is indicated by velocities dropping below 50 cm/s, rising above 190 cm/s, a change in flow direction in the main portal vein from hepatofugal to hepatopetal, or complete absence of flow (occlusion).