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May 2020

Focal Nodular Hyperplasia

Reviewers: Dharam Ramnani, MD |

Focal nodular hyperplasia (FNH) is not a true neoplasm but a tumor-like mass of benign hyperplastic hepatocytes. It is the 2nd most common benign liver nodule (after hemangioma).

It is a regenerative response of liver to a localized vascular anomaly/injury. Following associations have been noted: vascular lesions, such as cavernous hemangioma, epithelioid hemangioendothelioma, and hereditary hemorrhagic telangiectasia; hepatic venous outflow obstruction; orthotopic liver transplantation; and chronic alcohol abuse. There is no convincing relationship with oral contraceptive use.

Grossly, FNH is a subcapsular, pale yellow-brown or gray, solitary, well-circumscribed (but unencapsulated), firm, coarsely nodular lesion with a depressed central stellate scar. Fibrous strands radiate from the scar and divide the lesion into nodules. Hemorrhage and necrosis are uncommon. Contrast-enhanced CT or MRI of liver show FNH as a hypervascular lesion that enhances during the arterial phase with a non-enhancing central scar.

FNH comprises nodules of normal hepatocytes separated by fibrous bands that radiate from the central scar. There is some resemblance to cirrhosis. The fibrovascular stroma contains thick-walled dystrophic arteries, bile ductular proliferations, and inflammatory cell infiltrates. FNH lacks normal portal tracts but may contain intermediate- to large- caliber bile ducts within the central fibrous zone. Map-like staining pattern with glutamine synthetase is an important distinguishing feature from hepatocellular adenoma.

The differential diagnosis includes: hepatocellular adenoma, cirrhosis, and well-differentiated hepatocellular carcinoma. FNH can be safely left alone and monitored with periodic ultrasound. Larger or symptomatic lesions are removed by segmental resection or enucleation.

1. Goldblum, J. R. et al (2018). Rosai and Ackerman's Surgical Pathology - 11th Edition. Philadelphia, PA. Elsevier.
2. WHO Classification of Tumours. Digestive System Tumors, 5th Edition, 2019; IARC, Lyon, France.
3. Feldman, M., Friedman, L. S., & Brandt, L. J. (2016). Sleisenger & Fordtran's Gastrointestinal & Liver Disease - 10th Edition. Philadelphia, PA. Elsevier Saunders.

Focal Nodular Hyperplasia