Ultrasound Characteristics of Alcoholic Steatosis
Alcoholic steatosis on ultrasound appears as increased liver echogenicity (brightness) compared to the renal cortex, often with posterior beam attenuation, though ultrasound cannot distinguish alcoholic from non-alcoholic causes and has low sensitivity when steatosis is less than 30%. 1
Primary Ultrasound Features
The main characteristics include:
- Increased hepatic echogenicity: The liver parenchyma appears brighter than the adjacent renal cortex, which is the hallmark finding 2
- Posterior beam attenuation: Progressive weakening of the ultrasound signal as it penetrates deeper into the liver tissue, though this may paradoxically be absent in some cases of severe steatosis 3
- Hepatorenal contrast: The liver appears more echogenic (brighter) when directly compared to the right kidney cortex 4, 2
- Vascular blurring: Decreased visualization of intrahepatic vessels and the diaphragm due to increased echogenicity 4
Important Diagnostic Limitations
Ultrasound has significant limitations that must be recognized:
- Cannot differentiate etiology: Ultrasound findings are identical whether steatosis is alcoholic or non-alcoholic in origin 1, 5
- Poor sensitivity for mild disease: Detection requires at least 20-30% hepatic fat content; steatosis below this threshold is frequently missed 1
- Cannot distinguish simple steatosis from steatohepatitis: Ultrasound cannot identify inflammation or differentiate alcoholic steatohepatitis from simple fatty liver 1
- Subjective interpretation: Results depend heavily on operator experience and technique 1
- Technical challenges: Examination is difficult in obese patients 1
Advanced Ultrasound Techniques
Controlled Attenuation Parameter (CAP) via transient elastography provides quantitative assessment:
- Normal CAP range: 156-287 dB/m 1
- Cutoff values for steatosis severity: 250 dB/m (mild), 299 dB/m (moderate), 327 dB/m (severe) 1
- Can be performed simultaneously with liver stiffness measurement for fibrosis assessment 1
Clinical Role
Ultrasound serves as the first-line screening modality for suspected alcoholic liver disease due to its wide availability, ability to evaluate the entire hepatobiliary system, and robust performance for moderate-to-severe steatosis 1, 4. However, liver biopsy remains necessary for definitive diagnosis when aggressive treatment is considered, cofactors are suspected, or histologic confirmation of alcoholic steatohepatitis is required 1.
Common Pitfalls
- Do not assume increased echogenicity is always steatosis—cirrhosis, viral hepatitis, glycogen storage disease, and hemochromatosis can produce similar findings 2
- Absence of posterior attenuation does not exclude severe steatosis, as this can occur paradoxically in gross fatty infiltration 3
- Elevated liver stiffness measurements in patients with AST >100 U/L may be falsely elevated due to inflammation rather than fibrosis 1
- Clinical history (alcohol consumption >6 drinks/day) and AST:ALT ratio >2 provide better diagnostic clues than imaging alone 6