Natural history of liver imaging reporting and data system category 4 nodules in MRI

Purpose: The purpose of this study was to characterize the MR imaging features and outcomes of liver imaging reporting and data system (LI-RADS) category 4 (LR4) nodules, with an emphasis on upgrade to category 5 (LR5) and development of contraindications to curative therapy. Methods: Institutional review board approval was obtained for this retrospective, dual-institutional Health Insurance Portability and Accountability Act-compliant study. The requirement for informed consent was waived. Contrast-enhanced MRI studies performed on patients with cirrhosis were retrospectively assessed using LI-RADS 2014 by at least two readers. All nodules were individually evaluated to determine their major imaging features at diagnosis, and follow-up data were used to determine the associated imaging outcomes. Results: One hundred eighty-one untreated LR4 nodules in 139 patients had adequate imaging and follow-up for inclusion in the study. Most (61% [111/181]) of these demonstrated arterial phase hyperenhancement, washout, and diameter less than 20 mm. During the follow-up period (median 163 days), 31% (56/181) of the nodules upgraded to LR5, 40% (73/181) remained stable, and 29% (52/181) downgraded. Of the nodules that upgraded, 61% (34/56) increased their size category and 54% (30/56) developed newly visualized capsules. No LR4 nodules developed venous invasion, satellites nodules, or new intrahepatic or extrahepatic metastatic disease. 75% (42/56) of the nodules that upgraded to LR5 did so within 6 months. Conclusions: Approximately one-third of LR4 nodules upgrade to LR5, and the short-term risk of developing venous invasion or metastasis is very low.