Liver Attenuation in Polycythemia Vera

Critical Limitation of Contrast-Enhanced CT

The American College of Radiology states that contrast-enhanced CT is not useful for assessing liver attenuation or diagnosing hepatic steatosis because Hounsfield unit (HU) values are highly variable after contrast injection 1, 2, 3, 4
HU values on contrast-enhanced studies vary due to contrast injection timing, location of injection site, protocol differences, scan length, and patient's hemodynamic circulation 1, 2
Unlike unenhanced CT, where specific HU thresholds correlate with steatosis severity, no validated thresholds exist for contrast-enhanced studies 1, 2, 3

On unenhanced CT, liver attenuation <40 HU correlates with ≥30% steatosis, according to the American College of Radiology 2, 3, 4
Progressive attenuation decrease correlates with increasing fatty infiltration:

Ischemic hepatitis can cause hypoenhancement of liver parenchyma and is a serious condition that can progress to liver failure with high mortality, as reported by the American College of Radiology 1, 2
Contrast-enhanced CT can identify ischemic hepatitis and shock liver 1, 2

The American College of Radiology recommends reviewing the contrast-enhanced CT for heterogeneous enhancement patterns suggesting ischemia 1, 2
If decreased attenuation is noted on contrast CT and steatosis assessment is clinically indicated, obtain unenhanced CT or MRI without contrast for accurate quantification, as suggested by the American College of Radiology 2, 3, 4
MRI without contrast is superior to CT for diagnosing and grading steatosis, with sensitivity 76.7-90.0% and specificity 87.1-91% for detecting ≥5% hepatic fat 2, 3, 4
Unenhanced CT has 100% specificity and 82% sensitivity for moderate steatosis (≥30%) 2, 3, 4

Do not attempt to quantify liver fat content using HU measurements from contrast-enhanced CT—the values are unreliable and not validated, according to the American College of Radiology 1, 2, 3, 4
Do not assume decreased attenuation equals benign steatosis—ischemic liver injury is life-threatening and requires urgent recognition, as stated by the American College of Radiology 1, 2