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Hepatobiliary
Demonstration data

Hepatic Steatosis (CT)

Estimates hepatic fat using absolute liver attenuation and the liver–spleen difference on non-contrast CT.

Fat lowers the CT attenuation of the liver. On non-contrast CT a normal liver measures 50–65 HU and is a few HU denser than the spleen. A low absolute liver value, or a liver that is substantially less dense than the spleen, indicates hepatic steatosis.

🧮 Interactive Calculator

📐 Formula

L − S = liver attenuation − spleen attenuation (HU)

When to Use

  • Incidental assessment of hepatic fat on any non-contrast abdominal CT.
  • Screening potential living liver donors and follow-up of fatty liver disease.
  • Distinguishing diffuse steatosis from focal fat sparing/deposition when spleen serves as an internal reference.

How It Works

  • Place ROIs in uniform hepatic parenchyma, avoiding vessels, and in the spleen on the same non-contrast series.
  • Record the mean liver and spleen attenuation in HU.
  • Compute the liver–spleen difference (L − S).
  • Interpret using both the absolute liver value and L − S.

Interpreting the Result

  • Liver–spleen difference < −10 HU (liver more than 10 HU less dense than spleen) indicates moderate-to-severe steatosis.
  • Absolute liver attenuation < 40 HU also indicates moderate-to-severe steatosis.
  • Absolute liver attenuation < 48 HU corresponds to roughly >30% macrovesicular fat.

Limitations & Pitfalls

  • Only non-contrast CT thresholds are valid; contrast enhancement invalidates absolute cut-offs.
  • Iron overload, amiodarone, copper or glycogen raise liver density and can mask coexisting steatosis.
  • CT is insensitive to mild steatosis; MRI proton-density fat fraction is more accurate for low fat levels.

References

  • Kodama Y, Ng CS, Wu TT, et al. Comparison of CT methods for determining the fat content of the liver. AJR Am J Roentgenol. 2007;188(5):1307-1312.
  • Boyce CJ, Pickhardt PJ, Kim DH, et al. Hepatic steatosis (fatty liver disease) in asymptomatic adults identified by unenhanced low-dose CT. AJR Am J Roentgenol. 2010;194(3):623-628.

⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.