Interreader Agreement for Individual Ancillary Features in LI-RADS CT/MRI Version 2018: A Systematic Review and Meta-Analysis.

In LI-RADS CT/MRI version 2018 (v2018), ancillary features (AFs) support observation characterization and category assignment. Literature is lacking regarding interreader agreement of a broad range of AFs. To conduct a systematic review and meta-analysis of the interreader agreement of all individual AFs in LI-RADS CT/MRI v2018 and identify factors associated with interpretation variability. The MEDLINE, EMBASE, and Cochrane databases were searched for original research studies published from January 1, 2018 to September 15, 2025 that reported interreader agreement for individual AFs in LI-RADS CT/MRI v2018. Pooled kappa values for the 21 individual AFs were determined using a DerSimonian-Laird random-effects model with Knapp-Hartung adjustment. Study characteristics independently associated with agreement were identified by metaregression analyses. The final analysis included 47 studies totaling 11,891 patients and 13,695 hepatic observations. Three AFs (ultrasound visibility as discrete nodule, size stability ≥2 years, and size reduction) were not reported in any studies. The pooled kappa value among AFs favoring malignancy but not HCC in particular was 0.58 for subthreshold growth, 0.63 for corona enhancement, 0.69 for fat sparing in solid mass, 0.70 for transitional-phase hypointensity, 0.72 for iron sparing in solid mass, 0.75 for restricted diffusion, 0.77 for mild-moderate T2 hyperintensity, and 0.84 for hepatobiliary-phase hypointensity; among AFs favoring HCC in particular was 0.58 for nonenhancing capsule, 0.66 for nodule-in-nodule appearance, 0.69 for mosaic architecture, 0.72 for fat in mass more than adjacent liver, and 0.75 for blood products in mass; and among AFs favoring benignity was 0.26 for enhancement paralleling blood pool, 0.58 for hepatobiliary-phase isointensity, 0.59 for marked T2 hyperintensity, 0.60 for undistorted vessels, and 0.73 for iron in mass more than liver. In metaregression analyses, study characteristics showing significant independent associations with greater agreement for at least one AF included a proportion of patients with cirrhosis <80% and a modality of MRI only. Interreader agreement was generally higher for AFs favoring malignancy than for those favoring benignity. Cautious application of AFs in clinical practice is advised for the AFs associated with low agreement, particularly in the settings further contributing to reduced agreement.