Specificity of unenhanced CT for non-invasive diagnosis of hepatic steatosis: Implications for the investigation of the natural history of incidental steatosis

Abstract

Objectives To determine a highly specific liver attenuation threshold at unenhanced CT for biopsy-proven moderate to severe hepatic steatosis (≥30% at histology). Methods 315 asymptomatic adults (mean age±SD, 31.5± 10.1 years; 207 men, 108 women) underwent same-day unenhanced liver CT and ultrasound-guided liver biopsy. Blinded to biopsy results, CT liver attenuation was measured using standard region-of-interest methodology. Multiple linear regression analysis was used to assess the relationship of CT liver attenuation with patient age, gender, BMI, CT system, and hepatic fat and iron content. Results Thirty-nine subjects had moderate to severe steatosis and 276 had mild or no steatosis. A liver attenuation threshold of 48 HU was 100% specific (276/276) for moderate to severe steatosis, with no false-positives. Sensitivity, PPV and NPV at this HU threshold was 53.8%, 100% and 93.9%. Hepatic fat content was the overwhelming determinant of liver attenuation values, but CTsystem (P<0.001), and hepatic iron (P=0.035) also had a statistically significant independent association. Conclusions Unenhanced CT liver attenuation alone is highly specific for moderate to severe hepatic steatosis, allowing for confident non-invasive identification of large retrospective/prospective cohorts for natural history evaluation of incidental non-alcoholic fatty liver disease. Low sensitivity, however, precludes effective population screening at this threshold. Key Points • Unenhanced CT liver attenuation is highly specific for diagnosing moderate/severe hepatic steatosis. • Unenhanced CT can identify large cohorts for epidemiological studies of incidental steatosis. • Unenhanced CT is not, however, effective for population screening for hepatic steatosis. © European Society of Radiology 2012.