# About 20% of surgically resected HCC with <3cm in diameter is hypovascular.

# A small HCC may not show washout on delayed phase, which can be misinterpreted as arterial-portal shunt, a benign pseudo-lesion.

# Gadoxetic acid has advantage in hepatobiliary phase imaging, which enables to detect small HCCs and distinguish hypovascular HCCs from pre-malignant hepatocellular nodule known as dysplastic nodule.

# “Hypovascular hypointense nodule” is a new concept, which suggests early HCC and develop hypervascular (typical) HCC subsequently.

Audience will be able to understand in which scenario liver MRI is useful to determine management of cirrhotic patients with liver lesions.Standard healthcare for focal liver diseases include dynamic contrast-enhanced CT/MRI as problem solving tools. For MRI, conventional GBCA have been adopted as established diagnostic tool for over a decade (1). However, from the clinical point of view, the sensitivity and specificity of standard CT/MRI are not sufficiently high (2). For the sake of improving the outcomes of patients with focal liver disease, higher contrast between lesion and liver is required so that we can find small lesions and make the diagnosis at early clinical stage. Many researches studied the imaging features and diagnostic clues for HCC as well as hypovascular HCC, atypical HCC still often observed in the cirrhotic liver. Reviewing the available evidences, I will update the knowledge about atypical HCC and hypovascular hypointense nodule in the liver (3).

# Hepatobiliary contrast agents offer significantly higher sensitivity to detect HCC, especially if they are small (Fig.1); hepatobiliary phase image plays the major role for this improvement (3). Performing pre-operative MRI with hepatobiliary contrast agent can improve overall survival after surgical resection of HCCs (4).

# Hypovascular HCC account for up to 20% of HCCs with <3cm (5). Hypovascular HCC is supposed to be HCC at early stage of hepatocarcinogenesis (early HCC), which is derived from pre-malignant lesion called dysplastic nodule. Hypovascular HCC is supposed to become hyper-vascular HCC.

# Conventional imaging criteria cannot make non-invasive diagnosis of hypovascular HCCs. However, there are still some imaging features that suggest HCC, even though it is hypovascular. When comparing early HCC and dysplastic nodule, size is one of the most important factors that suggest HCC rather than dysplastic nodule, a premalignant lesion in cirrhosis. It is also a common sense that intra-lesional fat suggest HCC rather than dysplastic nodule. Hypervascular foci in the hypovascular nodule, also known as nodule-in-nodule appearance, is specific (but not sensitive) for HCC rather than dysplastic nodule.

# Hypointensity in hepatobiliary phase image obtained with hepatobiliary contrast agents is supposed to be the most sensitive imaging features that suggest HCC rather than dysplastic nodule (6, 7).

# Hypovascular hypointense nodule, a nodule in cirrhotic liver that shows hypovascularity in arterial phase and hypointensity in hepatobiliary phase, is of interest. It is most likely early (hypovascular) hepatocellular carcinoma (6) and has high prevalence to become hypervascular hepatocellular in a few years (8, 9). (Fig.3) Further, the presence of these nodules suggests that the underlying liver is at high risk of developing separate hepatocellular carcinoma in a future (10, 11). Treating hypovascular hypointense nodules probably prolong recurrence free survival after surgical resection of conventional HCCs (12).

Hypovascular HCC is sometimes observed in cirrhotic livers. Contrast-enhanced MRI with hepatobiliary contrast agents offers valuable information to determine clinical management of patients with liver cirrhosis.