Focal Nodular Hyperplasia

Epidemiology

Focal Nodular Hyperplasia is a benign hepatocytary tumor, more frequent when compared to the adenoma, with a prevalence of 3%. Due to technological progress in imaging techniques, prevalence may be superior (1%) (Hepatology 1995; 22: 1647-1681).

This tumor is diagnosed more frequently in women (age 30 years) in 30%, fortuitous or more frequently by ultrasound. The association with hemangioma is classic (20% of cases)(Gastroenterology 1989; 97: 154-157).

It is also thought to be caused by a secondary heaptocytary proliferation due to a vascular problem (local arterial hyperdebit) produced by a preexistent arterial anomaly (Hepatology 1995; 22: 1194-1200).

This hypothesis is suggested by the presence, inside the lesion, of a great arterial vessel, made up of a thick wall. It’s relationship with contraceptives appears to be nonexistent. A study showed the absence of influence of contraceptives with the size and number of FNH (Gastroenterology 2000; 118: 560-564 and Lancet 1998; 351: 1251-1252).

Clinical Manifestations and Biology

Even though 75% of cases  are asymptomatic, there may be clinical manifestations such as: pain, diarrhea, dyspepsia and rarely an inflammatory syndrome. Local complications may appear exceptionally, such as necrosis, hemoperitoneum and portal hypertension secondary to tumor compression.

Also, there exists the relationship with other vascular anomalies in other organs (aneurysms, Rendu-Osler disease, spider angyomata, portal vein atresia, arterial dysplasia, meningyomas, etc) (Gastroenterology 1995; 108: 1256-1262 and Gastroenterology 1999; 117: 284-285).

Pathological Anatomy 

It is more freuqently a unique tumor (74-80% cases), non encapsulated, sub-capsular, and varies in size (usually < 5 cm), located frequently in the inferior border of the liver (J Gastroenterol 1998; 33: 904-908).

Histologically, the tumor is made up of obstructed and sclerosed vessels. A biliary duct proliferation inside fibrous septa and the surrounding parenchyma is common. A mononuclear cellular infiltrate with steatosis and glycogen deposits or cholestasis can be observed (Gastroenterol Clin Biol 1980; 4: 364-375). Histology is typical in 80% of cases. A precise diagnosis is difficult to make in 20% of cases due to atypical forms.

Diagnosis

Ultrasound 

FNH appears as a isoechogenic tumor (45-54% of cases), hypoechogenic (30-41%) and hyperechogenic (3-25% of cases) (Hepatology 1995; 22: 1674-1681 and Br J Radiol 1998; 71: 1026-1032).

It has a homogenous echostructure. When the tumor is isoechogenic, it is diagnosed by its mass effect on surrounding structures. A central zone discretely hyperechogenic may be related to the central zone of fibrosis.

On a Doppler ultrasound, one may observe in the central fibrous zone, an arterial signal (Radiology 1993; 187: 113-117). The administration of contrast medium (CO2 microlobulles) augments the visualization of the central artery (Radiology 1991; 179: 377-382).

CT Scan 

This study is particularly important to view the kynesis of theses tumors. FNH is particular and is rapidly diagnosed. Previous to the injection of contrast medium, the lesion is isodense, homogenous. After the uptake, an intense lesion in the arterial phase can be seen. Stellar zone becomes isodense very rapidly during the portal phase (92% cases) (AJR 1997; 168: 1185-1192).

MRI 

After the injection of contrast medium  similar kinetics can be observed regarding CT scanning, and is common in  70% of cases (Hepatology 1995; 22: 1674-1681). Today, MRI is the most relevant method of diagnosis for this tumor.

Arteriography 

The tumor is hypervascular, with an opacification that appears early, in the center and spreads outwardly towards the periphery. This aspect is not specific of FNH. It is rarely used today, and exclusively for preoperative studies.

Practical Conduct and Treatment 

The evolution of theses tumors is benign. Follow-up shows generally an absence of size modifications (J Clin Ultrasound 1996; 24: 345-350 and Gastroenterology 2000; 118: 560-564), and in occassions, regression (J Comput Assist Tomogr 2000; 24: 61-66).

Rare cases of increasing in size have been reported, specially in multiple FNH (World J Surg 1997; 21: 983-991 and Hepatol 2000; 23: 9-11). The risk of malignant transformation is non-existent.

The differential diagnosis is mainly with the hepatic adenoma. In practice, ultrasound cannot differenciate between both tumors, so complementary methods have to be used (CT, MRI). In cases where apperas to be doubts, biopsy is recommended (World J Surg 2000; 24: 372-376).

The presence of a central fibrous scar in some occasions may signal a fibrolamellar carcinoma, specially if there are calcifications (Radiology 1996; 198: 889-892).  The fact that one has FNH as a diagnosis implies a “no treatment” attitude, knowing that there is zero risk of malignization and increasing in size.