Focal Nodular Hyperplasia (FNH) of the Liver

Abstract

Focal nodular hyperplasia (FNH) of the liver is a reactive mass-forming regenerative hyperplastic response of hepatocytes, secondary to localized vascular and circulatory abnormalities. FNH has a predilection for young females and represents, after hemangioma, the second most common benign hepatic tumorous lesion of the liver in adults. Many FNH are asymptomatic and detected by chance, but a minority of FNH are associated with various symptoms mainly related to large size or atypical location. Most FNH are solitary lesions that are predominantly located in the right liver lobe. In a minority of patients, multiple lesions, sometimes exceeding 30, are present. Macroscopically, FNH are well-circumscribed nodular, yellowish to tan masses with a characteristic nodular texture, radiating septa, and a central stellate scar-like fibrotic structure. Part of the lesions protrude from the liver and can become pedunculated masses. The diameter of FNH may exceed 20 cm. Histologically, FNH is characterized by nodules that consist of normal-looking hepatocytes forming thin plates. These nodules are separated from each other by fibrous septa and interspersed portal tract-like structures. The latter lack interlobular bile ducts but contain ductular proliferations. The fibrous tissue areas contain abnormal thick-walled blood vessels.

Benign Neoplasms, Mass‐Like Infections, and Pseudotumors That Mimic Hepatic Malignancy at MRI

“…FNH most commonly arises in premenopausal women, with a female‐to‐male ratio of 8:1 10,11 . FNH is a well‐circumscribed, unencapsulated lobulated mass composed of nonneoplastic, hyperplastic hepatocytes separated by fibrous septa that radiate from a central scar 12 . The scar contains dysmorphic arteries but no portal vein, and may be absent in lesions smaller than 3 cm 13 .…”

“…The pathogenesis of FNH is thought to relate to perfusion anomalies such as portal venule thrombosis or injury, which results in arterial to portal venous shunting 14–16 ; accordingly, FNH and nodular regenerative hyperplasia (NRH) are associated with vascular disorders such as hereditary hemorrhagic telangiectasia, congenital absence of the portal vein, and sinusoidal obstruction syndrome. FNH is increasingly diagnosed in children treated for hemato‐oncologic diseases, 12 and in patients receiving oxaliplatin‐based chemotherapy 17 . The pathogenesis is unclear but postulated to arise from chemotherapy‐induced sinusoidal obstruction 17 …”