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Focal Nodular Hyperplasia (FNH)

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Focal nodular hyperplasia (FNH), defined as a nodule composed of normal-appearing hepatocytes in an otherwise normal liver (30), is the second most common benign hepatic tumor after hemangioma. Histopathologically, FNH is categorized into two major groups: (i) classic (80%) and (ii) nonclassic (20%). The nonclassic-type is further subcategorized as the telangiectatic FNH (15%), FNH with cytologic atypia (3%) and mixed hyperplastic and adenomatous FNH (2%). Three key elements are present in classic FNH lesions including an abnormal nodular architecture, cholangiolar proliferation, and malformed vessels. In nonclassic-type, the cholangiolar proliferation is always present but one of the other two elements may be missing (31). In approximately…show more content…
When the central scar is large the conspicuity of the lesion increases (34). In some cases, a halo might be present around the lesion. It is thought that this halo represents compressed hepatic parenchyma or vessels and is more prominent when the lesion is located within a liver with steatosis. Contrast-enhanced US has been reported more accurate in detecting FNH. With using contrast materials an enhancement is possible and prominent feeding vessels may be seen in the arterial phase (34). In the portal venous phase, in contrast to hemangioma and hepatocellular adenoma, a centrifugal filling is seen and the enhancement is sustained in the portal venous phase (opposite to hepatocellular adenoma)…show more content…
In large hemangiomas, the central scar is typically brighter and larger on T2-weighted images. Because of the presence of calcifications, necrosis, and scar tissue the central scar in hepatocellular carcinoma shows low signal intensity on both T1- and T2-weighted images and the enhancement is slight (37).
The pseudocapsules around some FNH lesions result from compressed liver parenchyma and vessels surrounding the lesion and an inflammatory reaction. The pseudocapsule of FNH is often seen with high signal intensity on T2-weighted images and enhances on delayed contrast-enhanced sequences. In contrast to this pseudocapsule, the true capsule of hepatocellular carcinoma shows low signal intensity on both T1- and T2-weighted images, with persistent enhancement on delayed contrast-enhanced sequences (37).
Nuclear medicine: because of the presence of Kupffer cells in FNH, technetium 99m sulfur colloid can be taken up by this tumor. This ability differentiates FNH lesions from hepatocellular adenomas, hepatocellular carcinoma and hepatic metastasis that usually don’t have functionally active Kupffer cells
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