Diagnostic Value of Precontrast Low Attenuation as a LI-RADS CT Ancillary Feature for Hepatocellular Carcinoma.

Background Current CT ancillary features (AFs) have limitations, as several AFs are more evident at MRI. Precontrast low attenuation may serve as a potential AF in the Liver Imaging Reporting and Data System (LI-RADS). Purpose To evaluate the diagnostic value of precontrast low attenuation at CT as an additional AF for diagnosing hepatocellular carcinoma (HCC) and to assess its impact on LI-RADS diagnostic performance. Materials and Methods This retrospective study included adults at risk of HCC who underwent multiphase dynamic liver CT before hepatic resection or liver transplant at a tertiary referral facility between January and December 2022. Two radiologists assessed the presence of major features and AFs for each hepatic observation on the basis of LI-RADs categories, as follows: LR-3, intermediate probability of malignancy; LR-4, probably HCC; and LR-5, definitely HCC. Each lesion was assigned a LI-RADS category twice: first, by using AFs only (LI-RADS category with AFs only) and next, by using AFs with precontrast low attenuation (LI-RADS category with AFs and precontrast low attenuation). Precontrast low attenuation was defined as an attenuation of the target hepatic observation lower than that of the liver parenchyma based on visual assessment. Histopathologic analysis and clinical assessment were used as reference standards. The diagnostic performance of the two LI-RADS strategies was compared using generalized estimating equations. Results A total of 194 patients (mean age, 59 years ± 10 [SD]; 159 men) with 328 hepatic observations were included: 187 (57.0%) HCCs, 26 (7.9%) non-HCC malignancies, and 115 (35.1%) benign lesions. Precontrast low attenuation was associated with HCCs, yielding a diagnostic odds ratio of 9.1 (95% CI: 4.9, 16.6; < .001). Adding precontrast low attenuation upgraded 20 observations (17 HCCs and three dysplastic nodules) from LR-3 to LR-4, increasing the proportion of HCCs in LR-4 from 64.7% (22 of 34) to 72.2% (39 of 54). Compared with LR with AFs only, LR with AFs and precontrast low attenuation had a higher sensitivity (88.6% [163 of 187] vs 79.9% [146 of 187]; < .001), with no evidence of a difference in specificity (82.7% [121 of 141] vs 85.0% [124 of 141]; = .06). Conclusion Applying precontrast low attenuation at CT as an additional AF increased the proportion of HCCs in LR-4 and improved the sensitivity of LI-RADS for diagnosing HCC. © RSNA, 2025