Focal Nodular Hyperplasia (FNH) is a common benign liver lesion. It represents a non-cancerous growth within the liver that typically does not cause any symptoms. It is often discovered incidentally during imaging tests for other medical reasons.
Understanding This Liver Condition
Focal nodular hyperplasia is a regenerative mass lesion, not a true tumor, but rather a localized area of liver cells that have grown in an abnormal pattern. It is composed of normal liver cell components, including hepatocytes (the main liver cells), bile duct elements, and blood vessels, but these are arranged in a disorganized way. FNH has no potential to become malignant.
A characteristic feature of FNH is the presence of a central stellate scar, which is found in about 60-70% of cases. This scar serves as the focal point from which fibrous septa radiate outwards, creating a distinct spoke-wheel pattern. A large central artery typically supplies blood to the lesion, and unlike normal liver tissue, FNH lesions lack a portal vein supply.
FNH is the second most common benign liver lesion, with hepatic hemangiomas being the most frequent. It is found more often in women, with a ratio of approximately 8 or 9 women for every man affected. The condition is typically identified in younger to middle-aged adults.
The precise cause of FNH is not fully understood, but it is believed to be a response to an underlying blood vessel abnormality within the liver. This vascular anomaly leads to altered blood flow, stimulating the localized growth of liver cells. While some past discussions suggested a link to hormones like estrogen or oral contraceptive use, current evidence indicates these are not direct causes, though they might influence lesion size in some instances.
How Focal Nodular Hyperplasia is Diagnosed
Focal nodular hyperplasia is most frequently detected incidentally when individuals undergo imaging tests for unrelated health concerns. Since most people with FNH do not experience symptoms, this incidental finding then prompts further diagnostic evaluation to characterize the liver lesion.
Ultrasound can initially detect a liver lesion, but its specificity for FNH is low. Computed tomography (CT) scans can also suggest FNH, often showing a bright enhancement during contrast injection. However, CT may not always be definitive in distinguishing FNH from other liver masses.
Magnetic Resonance Imaging (MRI) with contrast agents is considered the gold standard for diagnosing FNH due to its ability to reveal characteristic features. Hepatocyte-specific contrast agents, such as gadoxetate disodium, are particularly useful as they are taken up by the liver cells within the FNH lesion, providing unique enhancement patterns that help differentiate it from other liver tumors. On MRI, FNH lesions typically show intense, homogeneous enhancement in the arterial phase, followed by becoming isointense (similar to normal liver tissue) in later phases, and the central scar often remains hypointense (darker) in early phases but may enhance later.
A liver biopsy is typically not required to diagnose FNH if the characteristic imaging features are present. Biopsies carry certain risks, but the distinctive appearance of FNH on advanced MRI often provides sufficient diagnostic confidence. A biopsy might only be considered in rare cases where imaging results are atypical or when there is persistent uncertainty about the diagnosis.
Living with Focal Nodular Hyperplasia
For most individuals, a diagnosis of focal nodular hyperplasia does not necessitate any specific treatment. These lesions are generally asymptomatic and do not affect the liver’s normal function. They rarely grow significantly, rupture, or bleed.
The usual approach to managing FNH is watchful waiting. Once the diagnosis is confidently established through imaging, particularly MRI, long-term follow-up imaging may not be routinely necessary. However, some physicians may recommend initial follow-up scans, such as MRI, to confirm the stability of the lesion over time.
Surgical removal is considered in only a few, very specific circumstances. This might include instances where the FNH lesion is causing significant symptoms, such as abdominal pain or a feeling of fullness, or if it grows to a very large size. Intervention may also be explored if imaging results remain inconclusive and differentiation from other liver lesions, like hepatic adenomas or cancerous tumors, cannot be definitively made.
Despite these rare exceptions, the prognosis for individuals diagnosed with focal nodular hyperplasia is excellent. The presence of FNH does not impair overall liver function or impact a person’s general health or life expectancy. Patients can typically continue with their normal daily activities without restriction once the diagnosis is confirmed.