Focal Nodular Hyperplasia

 

Focal nodular hyperplasia (FNH) is the second most common tumor of the liver, surpassed in prevalence only by hepatic hemangioma [1].FNH is a hyperplastic process in which all the normal constituents of the liver are present but in an abnormally organized pattern. Focal nodular hyperplasia is not a true neoplasm, but represents a local hyperplastic response of hepatocytes to a congenital vascular anomaly. [2,3]  It is a proliferation of normal, nonneoplastic hepatocytes that are abnormally arranged. FNH is usually solitary but can be multifocal in 20-30% of cases. The classic stellate central scar is only present in 15% to 33% of cases.   Although the use of contraceptive agents has not been implicated in the pathogenesis of FNH, their use is associated with an increase in the risk of complications for patients with FNH, and they may be a factor in the development of FNH. Although the pathophysiology is not completely understood, it is believed that a congenital arteriovenus malformation results in increased blood flow which, in turn, triggers hepatocellular hyperplasia [4]  Etiology of FNH is thought to be a hyperplastic response of the liver parenchyma to an anomalous arterial spider-like malformation [5] . This malformation induces changes in sinusoidal pressure, resulting in a reactive hyperplasia in the liver parenchyma [6]. In symptomatic females, hemorrhagic foci or infarctions may occur within the FNH; these are aggravated by administration of contraceptive agents. The rare complication of a spontaneous rupture into the peritoneum has also been associated with contraceptive use. (FNH),  benign  liver tumor, that occurs predominantly in women (80-90%) during the third to fifth decade. It represents the second most common liver  neoplasmafter cavernous  hemangioma and constitutes 8% of all liver tumours. It is now accepted that there is no aetiological role of contraceptives, although the use of contraceptives may stimulate the growth of the tumor .  FNH is presumed to originate as a hyperplastic response of the liver tissue to an underlying arteriovenous shunt or an abnormal focus of hyperperfusion.   The hallmark feature of the lesion is found on a cut specimen; the lesion appears as a central stellate scar with radiating fibrous septa dividing the tumor into lobules. The central scar contains an arterial malformation in which spiderlike branches supply the component nodules.  Focal nodular hyperplasia is subdivided into 2 types: classic (80%) and nonclassic (20%) [6] . Nonclassic FNH is further divided into 3 subtypes: telangiectatic FNH, FNH with cytologic atypia, and mixed hyperplastic and adenomatous FNH. In classic FNH, all 3 characteristic features are present: abnormal nodular architecture, malformed vessels, and cholangiolar proliferation. In nonclassic FNH, 2 of the 3 characteristic features are present; bile duct proliferation is always present [7] . In patients with asymptomatic, incidentally discovered FNH, no further investigation is required. Surgery for FNH is usually undertaken to resolve persistent symptoms or to establish a definitive tissue diagnosis when results of imaging are uncertain. Modern imaging techniques have improved diagnosis and thereby increased the incidence of FNH over the last two decades. Thus increasing use of modern imaging modalities FNH is becoming clinically more relevant. Ultrasonography is usually the initial imaging technique showing variable echogenicity lesion. The central scar can have an echogenic linear or stellate appearance. CT scan shows a homogeneous, well-defined isodense or hypodense lesion which becomes isodense in the delayed images with central hypodense scar. Magnetic resonance imaging can be helpful to differentiate FNH from other benign tumors. In post gadolinium delayed phase, FNH appeared hyperintense or isointense, whereas adenomas are hypointense. Arteriographic features of FNH include numerous dilated feeding arteries that enter the periphery of the  lesion and follow a centripetal course. It is not uncommonly for a larger artery  to enter directly into the centre of the lesion. During the parenchymatous phase a homogeneous and marked blush of the mass is observed.Technetium 99m sulphur colloid may demonstrate the reticuloendothelial function of these tumours. However, uptake will be present in only 50% of cases. In 50% of cases the radionuclide , notwithstanding the presence of Kupffer cells in the lesion , will accumulate to a lesser degree as in the normal liver. Tc-99m-labelled imino diacetic acid (IDA) analogues can be used to demonstrate the delayed excretion by the hepatocytes of the radionuclide and thus the delayed washout reflecting the absence of normal drainage of the small bile ducts present in the lesion.