FROM THE ARCHIVES OF THE AFIP

Focal nodular hyperplasia (FNH) is a benign hepatic tumor that likely represents a local hyperplastic response of hepatocytes to a congenita l vascular anomaly, It is most commonly seen in middle-aged women and is typically a solid mass measuring less than 5 cm in diameter. Most l esions have central scars that contain thick-walled vessels that provi de excellent arterial blood supply; hemorrhage, necrosis, and infarcti on are, therefore, extremely unusual, Characteristic imaging features include a hypervascular homogeneous tumor with a central scar and with both hepatocellular and reticuloendothelial function. Ultrasonography , computed tomography, scintigraphy, and magnetic resonance imaging al l offer different advantages in the detection and characterization of FNH. There is excellent correlation between the pathologic and imaging features of FNH. In many cases, it is possible to obtain a prospectiv e imaging diagnosis of FNH; however, in some cases, the distinction be tween FNH and other primary hepatic neoplasms is not possible. In thes e latter cases, close imaging follow-up, needle biopsy, or even surgic al resection may be necessary.