Focal nodular hyperplasia (FNH)
What is it?
Focal nodular hyperplasia (FNH) is the second most common benign liver tumor and occurs mainly in young women. FNH is usually small (<5 cm) and develops as a solid nodular formation in a normal liver. It occurs in the right or left hemisphere with the same frequency. The formation is chracterized by the presence of a central fibrous scar with radial septa, but this feature is not detected in 15% of cases. From a histological point of view, the FNH contains strands of normal hepatocytes separated by multiple fibrous septa originating from a central scar, which often contains an arterial vessel radially divided into smaller arterioles.
Causes and risk factors
The etiology, i.e., the cause of the development of FNH, is not very well known, but the most accepted theory is that it is based on an abnormality of vascular development. In the past, it was deemed that female sex hormones and oral contraceptives could be possible predisposing factors, but this relationship is still being debated.
Which are the symptoms?
Sometimes the tumor may cause some discomfort or abdominal pain, or other completely non-specific symptoms; in addition, with the exception of some sporadic cases, liver function tests are normal and alpha-fetoprotein (AFP) levels do not change.
How is it diagnosed?
In most patients, FNH is asymptomatic and most often it is detected accidentally during an examination (ultrasound, CT and MRI) for another disease.
On ultrasound examination, the FNH appears as a well-delineated, homogeneous formation with a central hyperechoic (i.e., clearer) scar. The use of a contrast agent for ultrasound, which makes it possible to visualize the morphology of the arteries of the tumor, helps in the differential diagnosis of adenoma. On CT, the central scar becomes hyperdense on later images, and on MRI, the characteristics of the scar and the lack of contrast capture of the capsule makes it possible to distinguish FNH from other formations with arterial enhancement (hepatocarcinoma, adenoma).
This way, thanks to advances in radiology, most cases of FNH can be diagnosed using traditional methods (CT and MRI) with a sufficient degree of confidence. Great difficulties arise in cases where a typical central scar is absent, and, consequently, it is difficult to make a differential diagnosis, choosing between a benign and malignant formation (in particular, fibrolamellar hepatocarcinoma). In these cases, the final diagnosis can only be established by histological examination (i.e., microscopic assessment of the characteristics of the tumor), and therefore it is sometimes necessary to offer surgical resection to the patient, since with a needle biopsy (i.e., aspiration of a very small amount of cell material performed with a thin needle) the result is unsatisfactory.
How is it treated?
As mentioned earlier, FNH is a benign formation, and therefore its development without surgical treatment is slow. In most cases, patients always remain asymptomatic, and complications such as rupture, bleeding and necrosis in the affected area are very rare. In addition, cases of malignant degeneration are not reported.
Therefore, treatment depends on the reliability of the diagnosis and symptoms. Asymptomatic patients with lesions characteristic of FNH do not need treatment. Conversely, if there is diagnostic uncertainty, surgery may be required for histological confirmation. Patients who experience persistent symptoms over a long period of time (and who are excluded from other major pathologies), or who experience an increase in the size of the tumor, may be referred for surgery.
Where do we treat it?
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