OBJECTIVE. Hepatic steatosis is a common incidental finding at radiologic imaging. The natural history of nonalcoholic fatty liver disease (NAFLD) and its associated risks for cardiovascular complications are not well established in this context. Our purpose was to investigate the clinical outcome of moderate-to-severe hepatic steatosis detected incidentally at CT.

MATERIALS AND METHODS. Liver attenuation was measured at unenhanced CT in 4412 consecutive adults scanned over a 12-month period. Moderate-to-severe steatosis was diagnosed by liver attenuation less than or equal to 45 HU, which is essentially 100% specific for histologic grading of 30% or more fat content. The control group was defined by a high-normal liver attenuation of 60–65 HU. The main exclusion criteria were preexisting liver disease (beyond asymptomatic NAFLD), alcoholism, or less than 1 year of clinical follow-up. A medical record review assessed for the development of symptomatic liver disease (including nonalcoholic steatohepatitis and cirrhosis) and seminal cardiovascular events (myocardial infarction, cerebrovascular accident, transient ischemic attacks, or coronary bypass or stent). Data for body mass index, diabetes, and liver enzyme levels were also recorded.

RESULTS. Five hundred three adults (11.4%) had unenhanced CT liver attenuation of 45 HU or less, yielding a final steatosis cohort of 282 patients after exclusions; the control group consisted of 768 patients after exclusions. The mean (± SD) patient age (51.4 ± 14.7 vs 50.8 ± 17.4 years), sex (53.9% vs 54.7% female), and mean follow-up intervals (7.3 ± 3.2 vs 7.7 ± 3.2 years) were similar between groups. No patient in either group had progression of liver disease beyond incidental steatosis. Subsequent cardiovascular events were more common in the steatosis cohort (9.9% vs 5.9%; p = 0.028), but steatosis was not an independent risk factor after controlling for diabetes and body mass index in multiple logistic regression analysis.

CONCLUSION. This longitudinal study failed to show progression of moderate-to-severe hepatic steatosis to symptomatic forms of fatty liver disease over a 5- to 10-year time horizon. Aggressive workup of hepatic steatosis found incidentally on imaging does not appear to be warranted. Steatosis was a biomarker for subsequent cardiovascular events but not an independent risk factor.