What is Focal Nodular Hyperplasia?
Your liver is the only organ inside your body that can heal itself. But this unique ability can also lead to the development of unusual growths in it. Although most of these growths are either solid or fluid-filled sacs, the reasons behind their formation can vary largely.
In 1958, a doctor named Hugh Edmondson first talked about a certain type of solid, non-cancerous liver growth, called focal nodular hyperplasia (FNH). Unlike hemangioma, which is the most common liver growth, FNH is believed to happen when the count of liver cells increases due to abnormal blood flow from certain odd arteries inside the liver.
Establishing the diagnosis and management of FNH can become difficult when it occurs alongside other health conditions. In the past, FNH was known by several other names, such as pavilion-shaped tumor, solitary growth due to excessive cell multiplication, localized liver scarring, and liver growth due to mixed cell types.
Because there was no clear category for this condition, a standard term was needed. In 1994, a group of international experts at the World Congresses of Gastroenterology agreed to use the term follicular nodular hyperplasia and classified it as a growth due to the liver’s healing ability. After this, FNH was clearly set apart from cancerous liver conditions.
What Causes Focal Nodular Hyperplasia?
Focal nodular hyperplasia (FNH), a type of liver growth, doesn’t have a well-established cause. However, it is believed to be triggered by abnormal blood vessels within the liver. These changes in how blood flows could result in the liver cells growing excessively in response.
It’s interesting to note that liver cells can respond with such growth both when blood flow is reduced and when it’s increased. Therefore, any pre-existing conditions that cause these blood vessel abnormalities might increase the chances of FNH developing.
Certain inherited conditions, such as hereditary hemorrhagic telangiectasia, also called Osler-Weber-Rendu syndrome, can lead to a higher occurrence of FNH. The presence of hemangiomas, which are non-cancerous masses of blood vessels, may also increase the chances of FNH.
However, understanding the exact causes becomes tricky as FNH can sometimes develop without any blood vessel abnormalities. The reasons for this remain unclear, and could be due to issues with biopsy samples or structural abnormalities that confuse the examination process.
Certain experts in the field of digestion and liver diseases believe that irregular blood flow in certain sections of the liver can lead to the cellular changes typically seen with FNH.
Key to distinguishing FNH from other types of liver growths is understanding its origin. Several studies have indicated that the liver cells within FNH growths come from multiple origins, leading to it being classified as a benign or harmless condition.
Evidence also suggests a potential genetic component to FNH. Studies show a higher occurrence of FNH in genetically identical (monozygotic) twins. However, researchers have yet to identify any particular genetic mutation that significantly increases the risk of developing FNH.
Risk Factors and Frequency for Focal Nodular Hyperplasia
In adults, the most frequently found benign liver lesion is the hemangioma, but the second most common is FNH, which is a type of non-hemangiomatous liver lesion. FNH makes up about 8% of these kinds of liver lesions. Even though FNH can appear as early as childhood, it’s usually found in women more than men, with a rough ratio of 8 to 1. Specifically, FNH is more common in women aged 20 to 50, which hints at a possible connection to increased estrogen levels. However, it’s important to note that it’s not proven that oral contraceptives cause FNH. Interestingly enough, women who take daily oral contraceptives usually have larger nodules than women who don’t. Larger nodules are also observed in women compared to men, regardless of contraceptive use.
In children, FNH is very rare. Its occurrence has mostly been reported in children who have undergone chemotherapy or stem cell therapy, or those with a history of cancer. For example, Baylor University Medical Center reported a case of FNH in a healthy 3-year-old girl who had no relevant medical history. She had surgery to remove a noticeable abdominal mass, which doctors initially thought was liver cancer. But after examining the mass, they discovered she actually had FNH.
Signs and Symptoms of Focal Nodular Hyperplasia
Focal nodular hyperplasia (FNH), a type of liver lesion, is mostly found unexpectedly during an imaging test for another abdominal issue. Although typically symptom-free, it may cause a detectable abdominal lump. This lump tends to be sensitive when the lesion is larger than 10 centimeters. These nodules are solo lesions, making liver enlargement uncommon. While it’s possible for the lesion to rupture spontaneously, this is extremely rare.
Testing for Focal Nodular Hyperplasia
Diagnosing focal nodular hyperplasia (FNH), a type of benign liver tumor, can involve a biopsy or various imaging techniques that show the typical characteristics of FNH and rule out other similar conditions. As part of the diagnostic process, your doctor might order lab tests, but these usually won’t show any significant abnormalities when FNH is present.
Alpha-fetoprotein, a substance often elevated in certain types of liver disease, will likely be within normal limits, further indicating that FNH tends to follow a harmless course. Other liver enzyme tests, such as serum alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and gamma-glutamyl transpeptidase (GGT), might show minor increases. However, these increases could also be due to other co-existing conditions as these enzymes are rarely elevated in cases of FNH alone.
Ultrasound is often the first imaging test used to check for liver problems, including FNH. However, its ability to spot FNH is relatively low (20%), so it’s not considered the top imaging choice for this condition. In ultrasound images, FNH usually appears as a light or dark mass with a brighter central area compared to the surrounding liver tissue. Some places outside of the United States use a technique called contrast-enhanced ultrasonography. Studies show this technique can help tell the difference between FNH and another liver condition called hepatocellular adenoma by showing detailed images of the arteries in the early phase of the test.
Although it’s not the absolute best imaging technique for diagnosing FNH, three-phase helical computed tomography (CT scan) with and without contrast dye injection is a cost-effective and reliable choice. Before the contrast dye is given, FNH tends to appear as a light or similar density mass with a central scar seen in about one-third of patients. During the liver’s arterial phase (when the liver’s arteries are filled with contrast dye), FNH usually appears brighter and then similar in density to the rest of the liver tissue during the portal venous phase. This makes the FNH blend in with the surrounding liver tissue.
Magnetic resonance imaging (MRI), a technique which generates detailed images of the body’s internal structures using magnetic fields, is excellent for diagnosing FNH. These images reveal that FNH appears as a light to dark lesion on T1-weighted images and light to very bright on T2-weighted images. Like the CT scan, the MRI shows the FNH to be enhanced during the arterial phase images. In the venous and delayed phase images, it becomes less noticeable. When a special contrast dye called gadobenate dimeglumine is used, MRI can achieve a sensitivity and specificity of 99% and 100%, respectively, making it the best diagnostic test for FNH.
Treatment Options for Focal Nodular Hyperplasia
Given the risks linked with biopsy or surgical procedures, coupled with the slow-growing nature of Focal Nodular Hyperplasia (FNH), a type of liver tumor, it’s often suggested to regularly monitor the condition with medical imaging every 3 to 6 months. Despite this, a biopsy or surgical removal may be necessary if the patient experiences symptoms or there’s a possibility of cancer after a non-conclusive biopsy, or if the tumor keeps growing. Surgical removal remains the most certain form of treatment.
FNH was first identified back in the 1960s, before birth control pills came into widespread use. Since then, no concrete evidence suggest that the occurrence of FNH has increased due to estrogen use. Nevertheless, almost all recorded cases of FNH that result in severe bleeding or rupturing have been found in patients using birth control pills. While stopping the use of birth control pills is not typically required, those taking estrogen therapy are advised to have follow-up imaging to monitor for any growth.
Additionally, for the younger population, it’s crucial to carefully evaluate the patient’s risk factors for cancer or liver disease.
What else can Focal Nodular Hyperplasia be?
When diagnosing focal nodular hyperplasia (a liver condition), there are several other conditions that may present similar symptoms and appear similar which doctors have to consider. These include:
- Hepatic adenoma (a rare liver tumor)
- Hepatocellular carcinoma (a type of liver cancer)
- Fibrolamellar hepatocellular carcinoma (a rare type of liver cancer)
- Hemangioma (a benign blood vessel tumor)
- Idiopathic noncirrhotic portal hypertension (a liver disorder causing high blood pressure)
- Regenerative nodules (liver tissue that has healed after damage)
- Metastatic disease (cancer that has spread to the liver from another part of the body)
