Focal Nodular Hyperplasia of the Liver
Focal nodular hyperplasia (FNH) is the second most common benign liver tumor after hemangioma, with a prevalence of 0.3% to 3% in the general population, requiring no intervention or monitoring in most cases as it has no malignant potential. 1
Definition and Pathophysiology
FNH is considered a congenital vascular malformation characterized by:
- A hyperplastic or regenerative response to hyperperfusion through anomalous arteries located in the center of these lesions 2
- Typically presents as a single lesion, though multiple lesions can occur 2
- Can be divided into two types:
Histologically, FNH is characterized by:
- Proliferation of normal hepatocytes without a prominent central scar
- Thin fibrous septa with a more or less apparent ductular reaction
- No true cirrhosis (sometimes called "pseudocirrhosis") 2
Epidemiology
- Affects females more commonly than males with an estimated sex ratio of 26:1 1
- Most commonly diagnosed in reproductive-aged women 2, 4
- May coexist with other vascular hepatic lesions such as hemangiomas in up to 20% of cases 2, 1
Diagnosis
FNH is typically diagnosed through imaging techniques:
Ultrasound Features
- Often appears hyperechogenic in B-mode images 2
- Color and power Doppler may show the pathognomonic "spoke-wheel" sign with a central feeding vessel 2
Contrast-Enhanced Ultrasound (CEUS) Features
- Strong hyperperfusion from a large, tortuous feeding artery in the arterial phase
- Enhancement pattern from center to periphery, producing a spoke-wheel appearance 2
CT and MRI Features
- Iso- or hypointense on T1-weighted images
- Slightly hyper- or isointense on T2-weighted images
- Hyperintense central scar on T2-weighted images
- Intense homogeneous enhancement during arterial phase
- Enhancement of the central scar during later phases 3
- MRI with liver-specific contrast agents has the highest sensitivity and specificity 1, 3
Differential Diagnosis
FNH must be differentiated from other hypervascular liver lesions:
Management
Conservative management is the standard of care for FNH, effective in approximately 94.4% of cases: 1
- No routine monitoring required after diagnosis
- No follow-up imaging necessary for asymptomatic FNH
- No intervention required regardless of size 1
Special Considerations
Pregnancy:
- No monitoring is required for FNH during pregnancy, regardless of size
- Pregnancy is not contraindicated in women with FNH
- Unlike hepatocellular adenomas, FNH poses minimal risk during pregnancy 2, 1
Oral Contraceptives:
- No established association between FNH and oral contraceptives
- Both contraceptive use and pregnancy are considered safe with FNH, with no monitoring required 2
Surgical Intervention
Surgical intervention is rarely indicated and should be considered only in specific circumstances:
- Persistent symptoms clearly attributable to FNH
- Unusual behavior
- Risk of rupture (extremely rare) 1, 5
Clinical Pitfalls and Caveats
Misdiagnosis risk: FNH can be mistaken for malignant lesions, potentially leading to unnecessary interventions 4, 6
Atypical presentations: Non-classical variants may lack the typical central scar, making diagnosis more challenging 2
Coexistence with other lesions: FNH may coexist with other vascular liver lesions, requiring careful evaluation 2, 1
Telangiectatic FNH: This variant may have a higher risk of bleeding, similar to adenomas 2
Biopsy considerations: In most cases, invasive diagnostic procedures can be avoided with appropriate imaging techniques 4
By understanding the characteristic features and benign nature of FNH, unnecessary interventions can be avoided, improving patient quality of life while maintaining appropriate surveillance when indicated.