Hepatic angiomyolipoma with minimal fat, mimicking hepatocellular carcinoma

An angiomyolipoma (AML) is a benign mesenchymal tumor composed of blood vessels, smooth muscle cells, and a varying amount of fat. The liver is the second most common site of AML involvement, after the kidney. In general, hepatic AML can be easily suggested as a diagnosis by identifying the abundant fatty component seen on computed tomography (CT) or magnetic resonance imaging (MRI). However, in some instances, intratumoral fat cannot be easily perceived on CT or even on MRI, and is known as AML with minimal fat. AML with minimal fat usually appears as a hypervascular mass on arterial phase images. Given the high incidence of hepatocellular carcinoma (HCC) in Korea, HCC should be put at the top of the differential diagnoses when we encounter a hypervascular hepatic mass. In general, AML shows the different enhancement pattern from that of HCC on portal and delayed phases. However, in the case of AML showing unusual imaging features, including a minimal fat component or an unusual enhancement pattern, AML can mimic HCC, which could thus lead to unnecessary treatment. Recently, liver-specific contrast agent (Gadoxetate disodium, Primovist, Bayer HealthCare, Germany) has been increasingly used to evaluate, detect, and characterize focal hepatic lesions. To the best of our knowledge, little is known regarding the imaging features of AML on gadoxetate disodiumenhanced MRI. We describe here one case of hepatic AML with minimal fat and an unusual enhancement pattern mimicking HCC on the imaging studies including gadoxetate disodium-enhanced MRI.