What are the characteristics and management of Hepatic Focal Nodular Hyperplasia (FNH)?

Hepatic Focal Nodular Hyperplasia: Characteristics and Management

Hepatic focal nodular hyperplasia (FNH) usually occurs in women of reproductive age, is not related to oral contraceptive use, rarely presents with abdominal pain, and does not carry a risk of spontaneous rupture.

Epidemiology and Demographics

• FNH is the second most common benign liver tumor after hemangioma, with a prevalence of 0.3% to 3% 1
• FNH is predominantly diagnosed in reproductive-aged women, with a female-to-male ratio estimated at 26:1 1
• The condition is commonly diagnosed incidentally during imaging studies performed for unrelated reasons 2

Relationship with Oral Contraceptives

• Unlike hepatic adenomas, the association between FNH and estrogen or oral contraceptive use is not well established 1
• While one case-control study found a history of prolonged combined hormonal contraceptive use was associated with FNH, another study found no association between contraceptive use and the size or number of lesions 1
• Current guidelines do not consider oral contraceptive use to be causally related to FNH development or growth 1

Clinical Presentation

• FNH is typically asymptomatic in most cases and rarely causes abdominal pain 2
• When symptoms do occur, they may include epigastric or right upper quadrant discomfort, but this is uncommon 2
• The majority of FNH lesions are discovered incidentally during imaging performed for other reasons 2, 3

Risk of Rupture

• Unlike hepatic adenomas, FNH has an extremely low risk of spontaneous rupture 1
• In the literature, only one case of hepatic rupture of FNH has been reported, making this an exceptionally rare complication 1
• The excellent arterial blood supply to FNH lesions makes hemorrhage, necrosis, and infarction extremely unusual 3
• This contrasts with hepatic adenomas, which carry a significant risk of rupture, especially during pregnancy 1

Imaging Characteristics

• FNH typically appears hyperechogenic on B-mode ultrasound images 1
• Characteristic imaging features include a hypervascular homogeneous tumor with a central scar 3
• On contrast-enhanced ultrasound (CEUS), FNH shows strong hyperperfusion from a large, tortuous feeding artery in the arterial phase, creating a spoke-wheel appearance 1
• After a few seconds, the lesion fills with contrast agent and appears more enhanced than the surrounding liver (the "lightbulb" sign) 1

Management Approach

• Once a correct diagnosis of FNH has been made, in most cases there is no indication for surgery 2
• Conservative clinical follow-up is recommended for asymptomatic patients 2
• Pregnancy is not contraindicated in women with FNH, and vaginal delivery is not associated with increased risks 1
• Imaging is not routinely recommended to monitor FNH during pregnancy 1
• Unlike hepatic adenomas, which require close monitoring during pregnancy, FNH does not require special surveillance 1

Potential Complications and Pitfalls

• The main clinical challenge is differentiating FNH from other hypervascular hepatic lesions such as hepatic adenoma, hepatocellular carcinoma, or hypervascular metastases 2
• FNH may coexist with other vascular hepatic lesions, such as hepatic hemangiomas, in up to 20% of cases 1
• Atypical imaging features can sometimes make diagnosis challenging, potentially requiring biopsy in uncertain cases 3
• Unlike hepatic adenomas, which may require intervention before pregnancy if >5cm, FNH does not require pre-pregnancy intervention regardless of size 1