Focal nodular hyperplasia (FNH) is a non-cancerous, benign liver condition characterized by the presence of a distinctive, well-defined lesion within the liver tissue. FNH is one of the most common benign liver lesions, often discovered incidentally during routine medical imaging studies. 

• Appearance: FNH typically appears as a solitary, round or oval-shaped nodule within the liver. It is known for its unique imaging characteristics, which include a central scar or stellate scar at the core of the lesion. This scar gives FNH a characteristic “bull’s-eye” or “target” appearance on imaging scans.
• Origins: The lesion in FNH arises from the abnormal growth of liver cells, particularly hepatocytes, which are the main functional cells of the liver. The exact cause of FNH is not always clear, but it is believed to be related to abnormal blood flow within the liver.
• Symptoms: Many individuals with FNH are asymptomatic, meaning they do not experience any noticeable symptoms. When symptoms do occur, they are typically mild and may include vague discomfort or a feeling of fullness in the upper right abdomen. Severe pain or complications are rare.
• Diagnosis: FNH is often diagnosed incidentally when imaging studies such as ultrasound, computed tomography (CT) scans, or magnetic resonance imaging (MRI) scans are conducted for unrelated medical reasons. The presence of a characteristic central scar and a well-defined, non-invasive nature of the lesion help distinguish FNH from other liver conditions.
• Differential Diagnosis: Healthcare providers may need to differentiate FNH from other liver lesions or tumors, such as hepatocellular adenoma or hepatocellular carcinoma (liver cancer). Imaging studies, along with clinical evaluation, are used to make this distinction.
• Natural History: FNH is generally a stable condition, meaning it does not tend to grow or change significantly over time. It is not associated with a risk of developing into liver cancer. In most cases, FNH remains a benign and non-threatening liver lesion.
• Treatment: Treatment for FNH is usually unnecessary unless the lesion causes significant symptoms or if there is diagnostic uncertainty. In rare cases, when symptoms are severe or when there are concerns about potential complications, surgical removal of the FNH lesion may be considered. However, this is typically reserved for specific situations, and the decision to intervene is made on a case-by-case basis.