From the Guidelines
Atypical focal nodular hyperplasia (FNH) of the liver is a benign growth that may not display the typical characteristics of classical FNH, such as a central scar, and its appearance on imaging can be variable. Unlike typical FNH, which is considered a hyperplastic or regenerative response to hyperperfusion through anomalous arteries located in the center of these lesions 1, atypical FNH may have irregular features that make it harder to distinguish from other liver conditions. These growths are not cancerous and generally don't require treatment unless they cause symptoms. Most patients with atypical FNH don't experience any symptoms, but some might feel discomfort or pain in the upper right abdomen if the lesion is large.
Key Characteristics of Atypical FNH
- May not have a central scar, which is a typical feature of classical FNH
- Variable appearance on imaging, making it harder to diagnose
- Not cancerous and rarely requires treatment
- May cause symptoms if the lesion is large, such as discomfort or pain in the upper right abdomen
We typically discover these growths incidentally during imaging tests done for other reasons. The cause isn't fully understood, but it may result from abnormal blood vessel formation in the liver, similar to classical FNH, which is considered to be a congenital vascular malformation 1. If you have atypical FNH, we'll monitor it with periodic imaging (ultrasound, CT, or MRI) to ensure it doesn't change in appearance or size, as recommended by current consensus and guidelines of contrast-enhanced ultrasound for the characterization of focal liver lesions 1. Surgery is rarely needed unless the diagnosis is uncertain or you're experiencing significant symptoms. You can continue normal activities without restrictions, and there's no need for dietary changes or medication. Women taking oral contraceptives can typically continue them, as the relationship between hormones and FNH growth remains unclear. The most important thing to understand is that atypical FNH is not cancer and won't turn into cancer, so while it requires monitoring, it shouldn't be a cause for significant concern.
From the Research
Definition and Presentation of Atypical Focal Nodular Hyperplasia
- Atypical focal nodular hyperplasia (FNH) of the liver is a rare benign hepatic tumor that can cause symptoms, unlike typical FNH which is usually asymptomatic 2.
- Atypical FNH can present with a range of symptoms, including pain, emesis, and a palpable mass in the right upper quadrant 2.
- The diagnosis of atypical FNH can be challenging, even with extensive work-up, due to its unusual presentation 2, 3.
Characteristics and Complications of Atypical Focal Nodular Hyperplasia
- Atypical FNH can be characterized by its large size, multiple lesions, and potential for rupture and bleeding 3.
- The risk of rupture and bleeding is higher in larger FNH lesions (>5 cm) 3.
- Atypical FNH can also cause compression of nearby structures, such as the hepatic vein, stomach, and biliary system 4.
Diagnosis and Management of Atypical Focal Nodular Hyperplasia
- The diagnosis of atypical FNH requires a combination of imaging techniques, such as computed tomography and angiography, and histopathological examination 2, 5.
- The management of atypical FNH depends on the presence of symptoms, the size of the lesion, and the risk of complications 4, 6.
- Surgical resection, radiofrequency ablation, or arterial embolization may be considered in cases of symptomatic atypical FNH or large lesions with a high risk of complications 4, 6.
Key Considerations in the Management of Atypical Focal Nodular Hyperplasia
- Systematic follow-up is the gold standard in asymptomatic patients with FNH 6.
- Elective surgery should be considered in symptomatic patients, those with marked enlargement, and in cases of uncertainty of diagnosis 6.
- The use of liver biopsy, imaging, and clinical context are important diagnostic tools in the diagnosis of atypical FNH 5.