How to identify hepatic steatosis, cirrhosis, and other liver conditions on an abdominal ultrasound?

How to Read an Abdominal Ultrasound for Liver Conditions: Identifying Hepatic Steatosis, Cirrhosis, and More

Ultrasound is the first-line imaging modality for evaluating hepatic steatosis and cirrhosis, with specific sonographic features that can help differentiate between these conditions when properly interpreted. 1

Hepatic Steatosis (Fatty Liver) Identification

Key Sonographic Features

• Liver Echogenicity:

  • Normal liver shows echogenicity similar to or slightly higher than normal renal cortex
  • Fatty infiltration increases liver echogenicity compared to the kidney 1

• Grading System:

  1. Mild steatosis:

     • Mild diffuse increase in liver echogenicity
     • Clear visualization of diaphragm and intrahepatic vessel walls
     • Minimal to no posterior beam attenuation

  2. Moderate steatosis:

     • Moderate diffuse increase in liver echogenicity
     • Obscuration of diaphragm and intrahepatic vessel walls
     • Moderate posterior beam attenuation

  3. Severe steatosis:

     • Marked increase in liver echogenicity
     • Non-visualization of diaphragm and intrahepatic vessel walls
     • Significant posterior beam attenuation 1

• Quantitative Assessment:

  • Hepatorenal index: Ratio of liver to kidney echogenicity
  • Shows excellent correlation with mild steatosis when compared to MR spectroscopy 1

Diagnostic Accuracy

• Sensitivity: 84.8% for moderate-severe steatosis (>30% fat on histology)
• Specificity: 93.6% for moderate-severe steatosis
• Lower sensitivity (53.3-65%) for mild steatosis 1

Pitfall

Steatosis can only be reliably diagnosed when fat content exceeds 30%. Lower amounts may be missed on conventional ultrasound 1.

Cirrhosis Identification

Key Sonographic Features

• Surface Nodularity: Most accurate finding for cirrhosis

  • More sensitive on the undersurface of the liver (86%) than superior surface (53%) 1
  • Look for irregular, wavy liver surface contour

• Liver Morphology Changes:

  • Atrophic right lobe
  • Hypertrophied caudate lobe and lateral segment of left lobe
  • Atrophied medial segment of left lobe
  • Right hepatic posterior "notch"
  • Expanded gallbladder fossa 1

• Vascular Changes:

  • Narrow hepatic veins (right hepatic vein <5 mm)
  • Enlarged caudate to right lobe ratio (modified ratio >0.90)
  • Enlargement of hilar periportal space (>10 mm thickness) 1

• Parenchymal Changes:

  • Coarsened or heterogeneous hepatic echotexture
  • Note: This is subjective and machine-dependent 1

Doppler Findings

• Portal Vein Changes:

  • Slow velocity or hepatofugal (reversed) flow direction in advanced cirrhosis
  • Portal vein diameter >13 mm suggests portal hypertension

• Hepatic Vein Changes:

  • Decreased phasicity of hepatic venous waveforms 1

Signs of Portal Hypertension

• Splenomegaly
• Portosystemic collaterals
• Ascites 1

Diagnostic Accuracy

• Sensitivity: 65-95% (highly variable)
• Specificity: 84.7%
• Positive predictive value: 98% 1, 2

Pitfalls

1. Sonographic appearance of hepatic steatosis and cirrhosis may overlap with a "fatty-fibrotic" pattern
2. Morphologic features are subjective and present only in later stages of fibrosis
3. Ultrasound is less reliable in obese patients due to poor beam penetration 1, 2

Differentiating Steatosis from Cirrhosis

Key Differentiating Features

Feature	Steatosis	Cirrhosis
Echogenicity	Bright, uniform	Coarse, heterogeneous
Surface	Smooth	Nodular, irregular
Liver size	Normal or enlarged	Often small (except in early stages)
Vascular structures	Normal caliber, clearly visible	Narrow hepatic veins, portal vein may be enlarged
Caudate lobe	Normal	Hypertrophied
Posterior beam attenuation	Present	Variable
Doppler findings	Normal flow patterns	May show portal hypertension signs

Advanced Assessment Techniques

1. Elastography:

   • Transient Elastography (TE) and Acoustic Radiation Force Impulse (ARFI) can quantify liver stiffness
   • Helps differentiate simple steatosis from steatosis with fibrosis
   • TE has sensitivity of 87% and specificity of 91% for diagnosing cirrhosis 1

2. Controlled Attenuation Parameter (CAP):

   • Quantifies degree of fat deposition in liver parenchyma
   • Normal range: 156-287 dB/m
   • Cutoff value of 276 dB/m for moderate-severe steatosis (sensitivity 83.3%, specificity 81.6%) 1

Mimickers of Cirrhosis on Ultrasound

Several conditions can mimic the appearance of cirrhosis on ultrasound:

1. Congenital hepatic fibrosis
2. Budd-Chiari Syndrome
3. Hepatoportal sclerosis
4. Cavernous transformation of portal vein
5. Pseudocirrhosis from metastatic disease
6. Acute liver failure
7. Post-therapeutic morphologic changes 3

Practical Scanning Protocol

1. Patient Preparation:

   • 6-hour fast before examination (reduces bowel gas)
   • Position patient supine or in slight left lateral decubitus

2. Standard Views:

   • Subcostal views of liver and portal structures
   • Intercostal views of right lobe
   • Left lobe views through epigastrium
   • Include comparison views of right kidney for echogenicity reference

3. Systematic Assessment:

   • Liver size and contour
   • Parenchymal echogenicity and texture
   • Portal and hepatic vessels with Doppler
   • Gallbladder and biliary system
   • Spleen size and appearance

Limitations and Caveats

1. Operator Dependency:

   • Significant inter-observer variability in assessment
   • Experience matters significantly in accurate interpretation

2. Technical Limitations:

   • Limited in obese patients
   • Bowel gas can obscure portions of the liver
   • Machine settings affect appearance of echogenicity

3. Diagnostic Challenges:

   • Cannot reliably distinguish NASH from simple steatosis
   • Early cirrhosis may be missed
   • Cannot detect inflammation without fibrosis 1, 4

Ultrasound remains a valuable first-line tool for liver assessment despite these limitations, especially when interpreted by experienced operators using standardized criteria and supplemented with elastography when available.