Focal nodular hyperplasia: findings at state-of-the-art MR imaging, US, CT, and pathologic analysis

Focal nodular hyperplasia (FNH) is the second most common benign liver tumor after hemangioma. FNH is classified into two types: classic (80% of cases) and nonclassic (20%). Distinction between FNH and other hypervascular liver lesions such as hepatocellular adenoma, hepatocellular carcinoma, and hypervascular metastases is critical to ensure proper treatment. An asymptomatic patient with FNH does not require biopsy or surgery. Magnetic resonance (MR) imaging has higher sensitivity and specificity for FNH than does ultrasonography or computed tomography. Typically, FNH is iso- or hypointense on T1-weighted images, is slightly hyper- or isointense on T2-weighted images, and has a hyperintense central scar on T2-weighted images. FNH demonstrates intense homogeneous enhancement during the arterial phase of gadolinium-enhanced imaging and enhancement of the central scar during later phases. Familiarity with the proper MR imaging technique and the spectrum of MR imaging findings is essential for correct diagnosis of FNH.