Ultrasound (US) LI-RADS: Outcomes of Category US-3 Observations.

OBJECTIVE. The purpose of the study is to evaluate the outcomes of ultrasound (US) LI-RADS category US-3 observations detected at US performed for hepatocellular carcinoma (HCC) screening and surveillance on the basis of subsequently performed multi-phase MRI or CT or histopathology. MATERIALS AND METHODS. In this retrospective analysis, 267 patients at high risk for HCC (161 men and 106 women; mean [± SD] age, 58.6 ± 12.2 years) underwent screening liver US between January 2017 and June 2019 and were assigned US-3 observations on a prospective clinical basis using the US LI-RADS algorithm. The results of follow-up imaging studies and/or histopathology were analyzed. RESULTS. Visualization scores assigned at US were A (40.8% [109/267]), B (52.8% [141/267]), and C (6.4% [17/267]). Reasons for US-3 observations included a measurable mass of 1 cm or larger (88.8% [237/267]; mean size, 1.8 ± 1.0 cm; range, 1.0-6.9 cm), an area of parenchymal distortion of 1 cm or greater (7.9% [21/267]; mean size, 1.8 ± 0.9 cm; range, 1.0-4.0 cm), or a new venous thrombus (3.4% [9/267]). Confirmatory testing with multiphase contrast-enhanced MRI or CT or with histopathology was available for 81.6% (218/267) of patients. Causes of US-3 observations included no abnormality at MRI or CT (41.3% [90/218]), a benign lesion (32.6% [71/218]), a LI-RADS category 3 (LR-3) observation at MRI or CT (5.5% [12/218]), a LI-RADS category 4 or 5 (LR-4 or LR-5) observation at MRI or CT or identification of HCC at histopathology (18.8% [41/218]), and an LR-M (denoting probably or definitely malignant but without specific features for HCC) observation at MRI or CT or other malignancy at histopathology (1.8% [4/218]). The PPV of a US-3 observation for probable or definite HCC was 18.8%, and for any malignancy it was 20.6%. CONCLUSION. In the HCC screening population, approximately one in five US-3 observations represents probable or definite HCC at multiphase MRI or CT or HCC at histopathology. These findings support current US LI-RADS guidelines to pursue further evaluation with multiphase cross-sectional imaging for US-3 observations.