Progression Rates of LR-2 and LR-3 Observations on MRI to Higher LI-RADS Categories in Patients at High Risk for Hepatocellular Carcinoma: A Retrospective Study.

Background: Reported rates of hepatocellular carcinoma (HCC) for LR-2 and LR-3 observations are generally greater than what may be expected based on clinical experience, possibly reflecting some studies' requirement for pathologic reference. Objective: To determine progression rates to higher LI-RADS categories of LR-2 and LR-3 observations in patients at high risk for HCC. Methods: This retrospective study included 91 patients (mean age 62 years; 64 men, 27 women) at high risk for HCC with clinically reported LR-2 (n=55) or LR-3 (n=36) observations on MRI and who also underwent follow-up CT or MRI after at least 12 months. A study coordinator annotated the location of a single LR-2 or LR-3 observation per patient, based on the clinical reports. Using LI-RADS v2018 criteria, two radiologists independently assigned LI-RADS categories on the follow-up examinations. Progression rates from LR-2 or LR-3 to higher categories were determined. A post hoc consensus review was performed of observations that progressed to LR-4 or LR-5. Subgroup analyses were performed with respect to presence or prior HCC (n=34) or a separate baseline LR-5 observation (n=12). Results: For LR-2 observations, progression to LR-4 was 0.0% (95% CI 0.0%-6.7%) and LR-5 was 3.6% (95% CI 0.4%-13.1%) for both readers. For LR-3 observations, progression to LR-4 was 22.2% (95% CI 9.6%-43.8%) and LR-5 was 11.1% (95% CI 3.0%-28.4%) for both readers. Fourteen observations progressed to LR-4 or LR-5 for both readers (post hoc analysis: no LR-2 to LR-4; two LR-2 to LR-5; eight LR-3 to LR-4; four LR-3 to LR-5). Progression rate from LR-3 to LR-5 was higher (p .99) between patients with versus without prior HCC. Conclusion: Based on progression to LR-4 or LR-5, LR-2 and LR-3 observations showed lower progression rates than reported in studies incorporating pathology in determining progression. Clinical Impact: The findings refine understanding of the clinical significance of LR-2 and LR-3 observations.