From the Guidelines
A fatty liver typically appears heterogeneous on ultrasound, but can also appear homogenous in cases of diffuse fatty infiltration. When fat accumulates in the liver, it can create areas of varying echogenicity (brightness) throughout the liver tissue, resulting in a heterogeneous appearance 1. This heterogeneity occurs because fat deposits are not uniformly distributed throughout the liver parenchyma. On ultrasound imaging, a fatty liver typically shows increased echogenicity compared to the kidney (hepatorenal contrast), vascular blurring where blood vessel walls become less distinct, and poor visualization of the diaphragm due to attenuation of the ultrasound beam. Some key points to consider when evaluating fatty liver on ultrasound include:
- The degree of heterogeneity often correlates with the severity of fatty infiltration, with more advanced cases showing more pronounced heterogeneous patterns 1.
- In cases of mild fatty infiltration, the liver may appear more homogeneously hyperechoic, making it challenging to distinguish from other liver conditions 1.
- The hepatorenal index can be used to quantify the degree of fatty infiltration, which has been shown to have an excellent correlation with fat fraction on MR spectroscopy and liver biopsy 1.
- The appearance of a fatty liver on ultrasound can be subjective and may be influenced by inter- and intraobserver variability, as well as confounding factors such as inflammation or fibrosis within the liver parenchyma 1.
From the Research
Fatty Liver Appearance on Ultrasound
- Fatty liver can appear as a homogeneous or heterogeneous pattern on ultrasound, depending on the distribution of fat accumulation in the liver 2.
- The heterogeneous pattern is more common, with fat accumulation appearing as areas of increased echogenicity compared to the surrounding liver parenchyma 3, 4.
- Diffuse fat accumulation, diffuse fat accumulation with focal sparing, and focal fat accumulation in an otherwise normal liver are common patterns of fatty liver disease on ultrasound 2.
- Unusual patterns, such as multinodular and perivascular accumulation, can also occur and may cause diagnostic confusion 2.
Diagnostic Considerations
- Ultrasound is a common modality used to evaluate the liver, but its sensitivity for detecting fatty liver disease can be reduced compared to other imaging modalities like MRI 3.
- The echogenic liver, defined as increased echogenicity of the liver parenchyma compared to the renal cortex, can be attributed to hepatic steatosis, but other hepatic and systemic diseases should also be considered 4.
- Knowledge of the different patterns of fat accumulation in the liver and their associated findings is essential for accurate diagnosis and differentiation from other liver diseases 2.