OVERVIEW
Focal nodular hyperplasia of the liver (FNH) is a rare benign lesion of the liver, which is one of the benign tumors of the liver after hepatic hemangioma, accounting for 8% of primary tumors of the liver, and the prevalence of FNH is about 0.9% in the population, and the cause of FNH is still unclear. Due to the development of imaging technology in recent years, the reports of focal nodular hyperplasia of the liver have gradually increased. In the past, there were various names in the literature, such as focal cirrhosis, hepatic malformation, hepatic inflammatory pseudotumor, etc. It was not until 1958 that Edmondson named it as focal nodular hyperplasia of the liver. This name was adopted by the World Health Organization in 1975 and the International Association for the Study of the Liver in 1976.
Etiology
It is currently believed that FNH is a proliferative response of the hepatic parenchyma to congenital arteriovenous malformations or is associated with limited reduction of blood supply due to inflammation, trauma, etc., rather than a tumor in the true sense of the word. Clinically, FNH is occasionally associated with vascular anomalies such as hemangiomas, which also supports the theory of congenital vascular anomalies. Some researchers also believe that the development of FNH may be related to estrogen.
Symptoms
The vast majority of patients with FNH are asymptomatic, with less than one-third of patients presenting with mild epigastric pain or abdominal masses. Often, FNH occurs by chance during a cesarean section or physical examination.
Symptomatic patients may present with right upper abdominal pain and discomfort, liver enlargement, or a right upper abdominal mass. Physical examination may reveal a hard mass in the liver under the right costal margin or in the right upper abdomen, which is tender, smooth, and moves up and down with respiration.
Examination
1. Laboratory examination
Liver function and AFP are mostly in the normal range.
2. Imaging examination
(1) Ultrasonography FNH is usually mildly hypoechoic or isoechoic, seldom hypoechoic, often with lobulated contours and hypoechoic halos, and the internal echoes of the mass are evenly distributed, with dotted line enhancement, clear margins, no periphery, and a star-shaped scar that is mildly hypoechoic. Color Doppler ultrasound showed that there was a thick artery in the center of the lesion radiating in all directions, and high arterial blood flow rate with low resistance was the characteristic manifestation of FNH.
(2) CT scan is hypointense or isointense, and in 1/3 of patients, hypointense stellate scar can be seen in the center of the mass; 89%-100% of the lesions have rapid, significant, and homogeneous enhancement in the arterial phase of enhancement, with hypointense or slightly hyperintense central scar; most of the lesions are isointense in the delayed phase, and the central scar can be isointense or hyperintense.
(3) MRI: Except for the scar, the signal is uniform, iso-signal or slightly low-signal in T1WI, and iso-signal or slightly high-signal in T2WI; after injection of Gd-DTPA, there are two typical dynamic enhancement modes: (1) FNH without scar is significantly enhanced in the arterial phase, and mildly to moderately enhanced or iso-signal or slightly low-signal in the portal vein phase and the delayed phase; (2) FNH with scar is significantly enhanced in the arterial phase (no enhancement of scar), and mildly to moderately enhanced or iso-signal in the portal vein phase. FNH with scarring has marked enhancement in the arterial phase (no enhancement in the portal vein phase), mild to moderate enhancement or equal or slightly low signal in the portal vein phase, and gradual enhancement in the portal vein and delayed phase of scarring.
(4) Angiography FNH shows a multivessel mass with central arterial blood supply and radial perfusion to the periphery, homogeneous staining in the parenchymal phase of the liver, filling defects in the portal venous phase, no invasion of the portal vein, no vascular leakage and arteriovenous fistulae.
(5) Nuclide examination Using 99mTc sulfur gel scintigraphy, 50% to 70% of FNH showed sulfur gel concentration, which could be differentiated from hepatocellular carcinoma and hepatic adenoma that did not contain Kuffer cells.
Diagnosis
It is mainly based on imaging examination; the combination of clinical manifestations and laboratory tests can lead to a preliminary diagnosis. Final diagnosis requires surgical resection of the lesion and histologic diagnosis.
Treatment
FNH is a benign lesion with no malignant tendency and rare complications, and the following consensus has been formed for its management: observation and follow-up of FNH is safe, and surgery should be avoided once the diagnosis is clear; surgical resection should be performed only if the tumor growth or tissue diagnosis is unclear.
Minimally invasive treatments including arterial embolization, radiofrequency ablation, and high-intensity focused ultrasound can be used for FNH with a clear diagnosis and clinical symptoms. Liver transplantation can be considered for a few cases with large masses or multifocal FNH causing liver failure.
For FNH found incidentally during dissection, the decision of whether to take surgery at the same time should be based on the size and location of the mass, the patient’s condition, and the experience of the operator. For asymptomatic FNH, it is best to perform only a simple liver tissue biopsy. The risk of complications from pregnancy and FNH is inconclusive, and prophylactic resection is not necessary in women who wish to become pregnant.
Prognosis
The disease is benign and has a favorable prognosis. The lesions develop extremely slowly. Rarely, deaths from ruptured nodes with hemorrhage and malignant transformation have been reported.