What is Focal Nodular Hyperplasia of the Liver?
Focal Nodular Hyperplasia is a benign tumor growth in the liver. Focal nodular hyperplasia is the second most common benign growth in the liver after hemangioma. Most cases are asymptomatic and are only diagnosed accidentally from imaging studies, while one third of the cases are discovered due to the emergence of clinical symptoms.
This is a benign tumor growth, and has rare tendencies to become malignant, these benign lesions rarely causes bleeding and does not grow rapidly.
The tumor growth in focal nodular hyperplasia has the following characteristics:
- Benign (no tendencies to be malignant)
- Has hepatocytes or liver cells
- Contains bile duct elements
- Presence of fibrous tissue formation
- Contains Kupffer cells
- hepatocyte hyperplasia or the increase in the number of cells is evident
Only a third of the cases of focal nodular hyperplasia shows symptoms. These cases may indicate an increased rate of cellular proliferation that is enough to cause signs and symptoms. Most cases are asymptomatic and are accidentally seen in X-Rays or CT scans.
When focal nodular hyperplasia is suspected or seen, it manifests the following clinical presentation:
- Gross feature is a scar with a stellate center, when the tumor is dissected and examined; a star-like scar is seen at the center of the growth.
- Large numbers of bland appearing hepatocytes proliferate the lobules of the liver And this is accompanied by the presence of bile compound and malformed blood vessels.
- Telangiectasia is also seen, this is a condition where small blood vessels become dilated. This is often accompanied by cellular changes such as dysplasia.
- Slower rate biliary secretion
- Tumors may be present on the liver surface or pedunculated
- Most lesions are smaller than 5cm most with an average diameter of 3 cm
- In some cases the lesion replace a lobe of the liver, this is then called Lobar Focal nodular hyperplasia
How Common is Focal Nodular Hyperplasia?
This is a rare condition with the following prevalence:
- 8% of liver tumors among adults is attributed to focal nodular hyperplasia. An approximate of 0.4-3% of the general population develops this condition. studies also reveal that the risk of focal nodular hyperplasia increases with age.
- For children, 2% of liver tumors are attributed to this condition. an estimated 2.25 per million children are affected by focal nodular hyperplasia. Focal nodular hyperplasia ranks third in the pediatric liver tumor diseases.
- Focal nodular hyperplasia is seen to occur in higher rates among females, but further studies are still done to explore this prevalence.
Symptoms and Signs
This is usually an incidental finding, meaning the condition is only known accidentally when the patient underwent an imaging test for evaluation of another disease. A symptom are usually rare and includes the following:
- Serum liver results that are abnormal
- Abdominal enlargement (especially on the right side)
- Palpable mass on the right upper abdomen
- Hepatomegaly or enlargement of the liver
- Weight loss
Causes and Pathogenesis
The exact cause of focal nodular hyperplasia is still unknown; however certain factors are seen to contribute to the formation of the benign lesions.
- Abnormalities in the blood vessels – The exact mechanism to why a person develops focal nodular hyperplasia is unknown but an accepted theory to why the disease emerges is the presence of abnormalities in the blood vessels. In focal nodular hyperplasia, additional networks of blood vessels and arterial malformations are seen. These abnormalities can either feed the liver cells with too much nutrients or oxygen or could leave them deprived of both. When either over nourishment and undernourishment happens, the cells increase in number
- Genetic abnormalities and inherited conditions – Focal nodular hyperplasia is also seen to occur in people with inherited conditions such as hemorrhagic telangiectasia. This is an inherited condition characterized by vascular malformations as well. This genetic predisposition causes vascular malformation in the liver and eventually leads to focal nodular hyperplasia.
- Past childhood malignancy – If a child had been treated for a past malignancy, he/she is at a higher risk of developing focal nodular hyperplasia. This is observed in clinical studies where 138 patients who received treatment for malignancies developed focal nodular hyperplasia. The incidence rate is at 045% of the cases.
- Color Doppler – Focal nodular hyperplasia (FNH) can be diagnosed with the use of imaging studies such as a color Doppler. Upon diagnosis a focal nodular hyperplasia would appear like a “comet tail”. This is because FNHs are hypervascular in nature; upon Doppler studies scattered veins and arteries are seen throughout the liver, giving a comet like appearance.
- Ultrasound – Ultrasound can also diagnose focal nodular hyperplasia since these tumors are isoechoic. But ultrasound studies can only detect tumors that are already pressing on to the adjacent structures or liver vessels. Ultrasound can only detect tumors with exerting mass effects.
- Ultrasound with Enhanced Contrast – This imaging study can help diagnose FNH by showing through contrast the classic sign of focal nodular hyperplasia: a central lesion that is non-enhancing and resembles a stellar shape.
- Low Index Contrast Enhanced Sonography – This diagnostic procedure enables the clinician to differentiate the condition from hepatic adenoma or other liver conditions. Focal nodular hyperplasia usually masks other liver conditions that need immediate or prompt treatment. Differential diagnosis to rule out focal nodular hyperplasia from any other forms of liver tumor formations is a priority intervention.
- Computed Tomography or CT Scan – A CT scan is usually done to point out the location, size and density of the tumor growth. A CT scan of a focal nodular dysplasia usually shows deformity in the contour of the liver, or a liver with a star shaped scar in the center. CT scans are often employed to give an overview of the growth but it doesn’t tell much about the characteristics of the tumor itself.
Imaging Studies that Reveal Characteristics of Focal Nodular Hyperplasia
- Nuclear Scintigraphy – This imaging study uses Sulphur colloid scan. 60% of focal nodular hyperplasia lesions would uptake this radiotracer, which is frequently seen in hepatic adenomas.
- MRI with Superparamagnetic Iron Oxide (SPIO) – MRI imaging enhanced with SPIO is used to determine the characteristics of focal nodular hyperplasia lesions. Since the lesions contain Kupffer cells, the contrast medium (SPIO) is greatly absorbed by the cells, indicating that the lesion is FNH in nature rather than an adenoma.
Resection of Focal Nodular Hyperplasic Liver – Surgery remains to be the primary mode of treatment. This is true for patients found to have the condition upon incidental finding or for those showing pronounced symptoms. Surgery involves the removal of the affected area (the tumor and some liver tissue or the entire lobe of the liver). After surgery follow up checkups are indicated to evaluate emergence of new tumors and the progression of their growth.
Indications for Surgery
This condition is rare and for most treatment nor surgery is not indicated. However on certain instances, a liver resection may be indicated:
- Lesions that are multiple
- Large lesions, probably greater than 5cm
- Liver enlargement or displacement due to the tumor formation
- Symptom producing tumors
- IF the behaves abnormally or increases size rapidly
- If there are signs of intra-lesional hemorrhage
Surgery involves liver resection. Liver resection is the removal of a part of the liver that is diseased or affected. In focal nodular hyperplasia, the part of the liver where there is tumor growth is removed. The healthy part of the liver is left unharmed. A person can still continue normal functioning despite the removal of one part of the liver.
Moderation in alcohol, medications and fat intake must be observed to prevent straining the liver. Of the right part of the liver is affected, the gallbladder may also be removed. Still if the removal of the gallbladder does not warrant a threat in one’s life. But dietary modifications and changes in lifestyle would be necessary.