Focal nodular hyperplasia

Ultrasound of malformed vessels within the fibrous scar of FNH.

Focal nodular hyperplasia's most recognizable gross feature is a central stellate scar seen in 60–70% of cases. Microscopically, a lobular proliferation of bland-appearing hepatocytes with a bile ductular proliferation and malformed vessels within the fibrous scar is the most common pattern. Other patterns include telangiectatic, hyperplastic-adenomatous, and lesions with focal large-cell dysplasia.[1] Rarely, these lesions may be multiple or can occur as part of a syndrome with hemangiomas, epithelioid hemangioendothelioma, hepatic adenomas, fibrolamellar hepatocellular carcinoma, vascular malformations of the brain, meningiomas, and/or astrocytomas.[1]

FNH is not a true neoplasm; it is believed to result from localized hyperplastic hepatocyte response to an underlying congenital arteriovenous malformation. It consists of normal liver constituents in an abnormally organized pattern, grows in a stellate pattern and may display central necrosis when large.[2] Additionally evidence suggests that the incidence of FNH is related to oral contraceptive use.[3]

Triple phase CT scan, or MRI are generally diagnostic. If still unable to differentiate from a hepatic adenoma, a sulfur colloid scan may be obtained. This will be positive in FNH, but not in an adenoma due to less Kupffer cells being present to uptake the colloid.