Focal nodular hyperplasia (FNH) is a benign nodule formed in the liver by histologically normal (or nearly normal) hepatocytes, accounting for approximately 8% of all primary liver tumors and the second most prevalent benign liver lesion, after hepatic hemangioma.FNH was first reported by Endmondson in 1958 FNH was first reported by Endmondson in 1958 and was previously misdiagnosed as hepatic adenoma, biliary hepatocellular malformation tumor, and focal nodular sclerosis. The exact etiology of FNH is still not well understood, and most scholars believe that it is a reactive proliferative change of hepatocytes in response to local vascular abnormalities, rather than a true tumor. the link between FNH and oral contraceptives is inconclusive, and the use of oral contraceptives does not increase the incidence of FNH, but may promote its growth. the pathology of FNH is divided into two categories: classic and atypical. The classic features include (1) abnormal nodule-like structures, (2) malformed vessels, and (3) proliferating bile ducts. Stellate purpura fibrous tissue is seen in the center of the lesion section, forming intervals radiating in all directions and dividing the mass. Atypia can be subdivided into three categories: capillary dilated, mixed hyperplastic and adenomatous, and cellular atypia. The lesions may lack abnormal structural nodules or malformed vessels, but proliferating bile ducts are always present. Most present as a heterogeneous adenomatous pattern with poorly defined contours, and almost all lesions lack scarring visible to the naked eye. The vast majority of patients with FNH are asymptomatic and are seen by incidental finding of an occupying lesion in the liver, and less than 1/3 of patients have clinical manifestations such as mild epigastric pain, discomfort, or abdominal masses. preoperative diagnosis of FNH relies primarily on imaging, and some scholars have compared pathologic findings with imaging diagnosis and found that about 70% of FNH can be diagnosed by imaging, and almost all cases diagnosed by imaging are classic FNH. Although pathological diagnosis is the gold standard, liver aspiration biopsy is of limited value, because FNH with atypical imaging is often atypical microscopically as well. Ultrasonography can show continuous enhancement of the lesion in the arterial and portal phases, which is an important differentiator between FNH and hepatic adenoma and hepatocellular carcinoma. The typical MRI features of FNH include: uniform signal except for the scar; significant enhancement in the arterial phase; low signal in T1 and high signal in T2 of the scar, no enhancement in the arterial and portal phases, and enhancement in the delayed phase (some lesions can be enhanced in the portal phase). Angiography showed that the FNH lesions were multivessel masses, characterized by central arterial supply and radiolucent perfusion to the periphery, with uniform staining in the hepatic parenchymal phase and filling defects in the portal venous phase. FNH is a benign non-neoplastic lesion that is generally not malignant. If MRI and other imaging examinations show typical FNH imaging manifestations, combined with no history of hepatitis and normal tumor markers AFP and CA199, FNH can be diagnosed clinically, and if patients have no clinical symptoms they can be followed up and observed regularly. Long-term follow-up studies have shown that FNH lesions do not increase in size during conservative treatment, and even decrease or disappear after discontinuation of oral contraceptives in some patients. ruptured FNH bleeding is also rare, and more than 80% of ruptured FNH bleeding cases have lesions >5 cm, which may suggest that the risk of ruptured FNH bleeding is significantly higher in lesions >5 cm, and surgical excision of such lesions may be the most appropriate. Terkivatan believes that FNH >4 cm in diameter often causes abdominal symptoms due to compression of surrounding tissue or the hepatic tegument. Therefore, an FNH >4 cm in diameter with symptoms is also an indication for surgery. We believe that the indications for FNH surgery should be: (1) progressive enlargement of FNH lesions during the follow-up period (2) clear diagnosis of FNH but with obvious clinical symptoms, especially lesions larger than 4 cm (3) clear diagnosis of FNH but with risk of rupture and bleeding (lesions larger than 5 cm) (4) unclear diagnosis of FNH and failure to exclude hepatic adenoma and hepatocellular carcinoma. In cases with surgical indication, surgical resection is still the first choice. However, for deep or central liver tumors less than 3 cm, radiofrequency ablation or microwave ablation can achieve treatment results equivalent to surgery with much less trauma and can be preferred. For patients who cannot tolerate surgery, catheter artery embolization is also a safe and effective alternative treatment, taking advantage of the fact that FNH is often supplied by a single artery.