Evaluation of LI-RADS 3 category by magnetic resonance in US-detected nodules ≤ 2 cm in cirrhotic patients

Liver Imaging Reporting and Data System (LI-RADS) for hepatocellular carcinoma (HCC) diagnosis in high-risk patients is a dynamic system, which was lastly updated in 2018. We aimed to evaluate the accuracy for HCC diagnosis of LI-RADS v2018 with magnetic resonance imaging (MRI) with extracellular contrast for solitary nodules ≤ 20 mm detected during ultrasound (US) surveillance in cirrhotic patients, with particular interest in those observations categorized as LI-RADS 3. Between November 2003 and February 2017, we included 262 consecutive cirrhotic patients with a newly US-detected solitary ≤ 20-mm nodule. A LI-RADS (LR) v2018 category was retrospectively assigned. The diagnostic accuracy for each LR category was described, and the main MRI findings associated with HCC diagnosis were analyzed. Final diagnoses were as follows: 197 HCC (75.2%), 5 cholangiocarcinoma (1.9%), 2 metastasis (0.8%), and 58 benign lesions (22.1%); 0/15 (0%) LR-1, 6/26 (23.1%) LR-2, 51/74 (68.9%) LR-3, 11/12 (91.7%) LR-4, 126/127 (99.2%) LR-5, and 3/8 (37.5%) LR-M were HCC. LR-5 category displayed a sensitivity and specificity of 64% (95% CI, 56.8–70.7) and 98.5% (95% CI, 91.7–100), respectively. Considering also LR-4 as diagnostic for HCC, the sensitivity slightly increased to 69.5% (95% CI, 62.6–75.9) with minor impact on specificity (96.2%; 95% CI, 89.3–99.6). Regarding LR-3 observations, 51 out of 74 were HCC, 2 were non-HCC malignancies, and 20 out of 21 LR-3 nodules > 15 mm (95.2%) were finally categorized as HCC. The high probability of HCC in US-detected LR-3 observations (68.9%) justifies triggering an active diagnostic work-up if intended to diagnose HCC at a very early stage. • In cirrhotic patients with nodules ≤ 20 mm detected during US surveillance, 51 out of 74 (68.9%) of LR-3 nodules by MRI corresponded to an HCC. • In LR-3 nodules, HCC diagnosis was closely related to baseline tumor size. All 5 nodules smaller than 1 cm were diagnosed as benign. Oppositely, 20 out of 21 LR-3 observations > 15 mm (95.2%) were diagnosed as HCC. • The high probability of HCC in US-detected LR-3 observations justifies triggering an active diagnostic work-up if intended to diagnose HCC at a very early stage.