Longitudinal evolution of CT and MRI LI-RADS v2014 category 1, 2, 3, and 4 observations

Abstract

Objectives: This study assesses the risk of progression of Liver Imaging Reporting and Data System (LI-RADS) categories, and the effects of inter-exam changes in modality or radiologist on LI-RADS categorization.

Methods: Clinical LI-RADS v2014 CT and MRI exams at our institution between January 2014 and September 2017 were retrospectively identified. Untreated LR-1, LR-2, LR-3, and LR-4 observations with at least one follow-up exam were included. Three hundred and seventy-two observations in 214 patients (149 male, 65 female, mean age 61 ± 10 years) were included during the study period (715 exams total). Cumulative incidence curves for progression to malignant LI-RADS categories (LR-5 or LR-M) and to LR-4 or higher were generated for each index category and compared using log-rank tests with a resampling extension. Relationships between inter-exam changes in LI-RADS category and modality or radiologist, adjusted for inter-exam time intervals, were modeled using mixed effect logistic regressions.

Results: Median inter-exam follow-up interval and total follow-up duration were 123 and 227 days, respectively. Index LR-1, LR-2, LR-3, and LR-4 differed significantly in their cumulative incidences of progression to malignant categories (p < 0.0001), which were 0%, 2%, 7%, and 32% at 6 months, respectively. Index LR-1, LR-2, and LR-3 differed significantly in cumulative incidences of progression to LR-4 or higher (p = 0.003). MRI-MRI exam pairs had more stable LI-RADS categorization compared to CT-CT (OR = 0.460, p = 0.0018).

Conclusions: LI-RADS observations demonstrate increasing risk of progression to malignancy with increasing category ranging from 0% for LR-1 to 32% for LR-4 at 6 months. Inter-exam modality changes are associated with LI-RADS category changes.

Key points: • While the majority of LR-2 observations remain stable over long-term follow-up, LR-3 and especially LR-4 observations have a higher risk for category progression. • Category transitions between sequential exams using different modalities (CT vs. MRI) may reflect modality differences rather than biological change. MRI, especially with the same type of contrast agent, may provide the most reproducible categorization, although this needs additional validation. • In a clinical practice setting, in which radiologists refer to prior imaging and reports, there was no significant association between changes in radiologist and changes in LI-RADS categorization.

Keywords: Hepatic neoplasms; Hepatocellular carcinoma; Liver; Longitudinal studies; Observer variation.

Figure 1:

LI-RADS category transitions summarizing index (rows) and final categories (columns) of 372 unique LR-1 to LR-4 observations are shown. Cells corresponding to observations that were stable in category are color-coded. Percentages are shown in parentheses for non-zero counts.

Figure 2:

Flow diagram illustrating the counts of each observation transition at the end of follow-up. Although the most of observations remained stable, observations exhibited significantly different rates of progression to higher LI-RADS categories based on their index category.

Figure 3:

Category progression and imaging feature evolution as extracted from sequential radiology reports. Observation in hepatic segment 5/8 measured 7 mm, demonstrated arterial phase hyperenhancement (APHE, arrow) without definite washout or capsule appearance, and was categorized LR-2 on index exam. The observation subsequently grew, evolved in its imaging features, and progressed in LI-RADS category on follow-up exams at 4, 7, 11, and 15 months. In retrospect, the observation was hyperintense on high-b-value diffusion weighted image (DWI) on index exam, indicating restricted diffusion. The observation should have been categorized LR-3, but this ancillary feature was unrecognized by the radiologist (*). AP: arterial phase images; T2: T2-weighted images. T2 hyperintense: mild-moderate T2 hyperintensity.

Figure 4:

Cumulative incidence curves for progression to LR-5 or LR-M shown for LR-1 (green), LR-2 (light green), LR-3 (yellow), and LR-4 (orange). Vertical bars indicate statistically significant pairwise comparisons assessed using Bonferroni-corrected log-rank tests with a resampling extension.

Figure 5:

Cumulative incidence curves for progression to LR-4 or higher shown for LR-1 (green), LR-2 (light green), and LR-3 (yellow). Vertical bars indicate the statistically significant pairwise comparison assessed using a Bonferroni-corrected log-rank test with a resampling extension.