Different histopathological manifestations of focal liver lesions show varying common and uncommon imaging findings and some pathologies may show similar appearance despite of different histopathology. It is necessary to characterise focal liver lesions accurately as not only benign and malignant lesions are managed differently, but also certain benign lesions have differing management. These lesions are increasingly being detected due to rapid growth of use of cross-sectional imaging as well as improvement in image quality and new imaging techniques. Contrast enhanced magnetic resonance imaging (MRI) is considered the gold standard technique in characterising focal liver lesions. Addition of gadoxetic acid has been shown to significantly increase diagnostic accuracy in the detection and characterization of liver abnormalities. Classic imaging characteristics of common liver lesions, including their behaviour on gadoxetic acid enhanced MRI, have been described in literature over recent years. It is important to be familiar with the typical aspects of these lesions as well as know the uncommon and overlapping imaging features to reach an accurate diagnosis. In this article, we will review the well-described characteristic imaging findings of common and rare focal liver lesions and present several challenging cases encountered in the clinical setting, namely hepatocellular adenoma, focal nodular hyperplasia, hepatic angiomyolipoma, hepatocellular carcinoma, intrahepatic cholangiocarcinoma, neuroendocrine tumours as well as a pleomorphic liposarcoma of the liver.

Indocyanine green (ICG) excretory defect is characterized by an ICG retention rate of more than 50% at 15 min without any other abnormal liver functions. The incidence of ICG excretory defect is 0.007% in the Japanese population. Due to its rarity, the imaging characteristics associated with ICG excretory defect remain unclear. Herein, we present three cases of ICG excretory defect, which showed impaired lesion detectability on gadoxetic acid-enhanced MR imaging (EOB-MRI). In the hepatobiliary phase (HBP) of EOB-MRI, diminished enhancement of the liver parenchyma, prolonged intravascular enhancement, and attenuated gadoxetic acid excretion to the bile duct were observed. Our study also investigated the expression level of organic anion transporting polypeptide (OATP) 1B3 and OATP1B1/1B3, which is related to the uptake of ICG and gadoxetic acid into hepatocytes. All cases showed decreased expression of OATP1B3, which was assumed to be characteristic of ICG excretory defect. The present study indicates that, when patients with ICG excretory defect are evaluated using EOB-MRI, attention should be paid to the impaired lesion detectability in the HBP due to the attenuated gadoxetic acid uptake into the liver parenchyma.

Hypervascular hyperplastic nodules (HHNs) occasionally develop in patients with alcoholic liver cirrhosis (ALC) and show arterial enhancement, thus mimicking hepatocellular carcinoma (HCC). Importantly, HHN as a benign lesion should be distinguished from HCC.
To evaluate the value of gadoxetic acid-enhanced MRI (Gd-EOB-MRI) and diffusion-weighted imaging (DWI) in distinguishing HHN from small (<3 cm) hypervascular HCC (hHCC) in patients with ALC.
Retrospective case-control study.
3.0T/in- and out-of-phase, T1 -weighted, T2 -weighted, diffusion-weighted, apparent diffusion coefficient, and dynamic gadoxetic acid-enhanced images.
Among 560 patients with ALC who underwent Gd-EOB-MRI and DWI, 12 patients with 28 HHNs and 22 patients with 29 hHCCs smaller than 3 cm were included.
The following MRI features were evaluated by three independent radiologists: signal intensity (SI) on T1 -weighted, T2 -weighted, diffusion-weighted, and hepatobiliary phase (HBP) images; shape, homogeneity, and margin on HBP; diffusion restriction; intralesional fat; necrosis; hemorrhage; washout on portal venous phase (PVP) and/or transitional phase (TP); and capsular enhancement. Quantitative analysis was also conducted.
Univariate and multivariate analyses were performed to determine the significant MRI findings, and their diagnostic performance for the prediction of HHN was analyzed.
Lesion size of ≤16 mm (odds ratio [OR], 24.41; P = 0.007), low-to-iso SI on DWI (OR, 26.92; P = 0.007), and absence of washout on PVP and/or TP (OR, 31.84; P = 0.009) were significant independent factors for predicting HHN. When all three criteria were satisfied, the specificity was 100%. Compared with hHCCs, HHNs showed significantly smaller size (mean, 13.8 mm vs. 19.9 mm; P < 0.001) and higher mean SI value (994.0 vs. 669.5) and lesion-to-liver SI ratio (1.045 vs. 0.806) on HBP (P < 0.001, respectively).
Gd-EOB-MRI and DWI may be helpful in differentiating HHN from small hHCC in patients with ALC.
3 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:70-80.