Focal Nodular Hyperplasia (FNH): A Comprehensive Review of the Common Benign Liver Lesion

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🧐 Introduction: Understanding Focal Nodular Hyperplasia (FNH)

Focal Nodular Hyperplasia (FNH) is one of the most common benign liver lesions in adults. It is often an incidental finding but can occasionally present with symptoms. This comprehensive column, based on a case study of a 31-year-old woman with intermittent abdominal pain, delves into the essential aspects of FNH, from its underlying mechanism to its characteristic imaging features and management.

🔬 Pathophysiology of Focal Nodular Hyperplasia (FNH)

Focal Nodular Hyperplasia is generally regarded as a hyperplastic process rather than a true neoplastic growth.

  • Histological Structure: The classic form of FNH is described as a solitary tumor mass composed of nodular parenchymal proliferation/hyperplasia, often surrounded by fibrous septa and thickened liver plates.
  • The Central Scar: A key pathological and radiological feature is the central, stellate scar. Histologically, this central scar is made up of fibrous connective tissue, mature collagen, abnormal arteries, and draining veins. This structure forms a pseudocapsule, helping to differentiate it from other liver lesions like hepatocellular carcinoma or adenoma.
  • Malignancy Risk: It is crucial to remember that FNH is a common benign liver lesion that is not recognized to have a malignant potential.

🌍 Epidemiology of Focal Nodular Hyperplasia (FNH)

Focal Nodular Hyperplasia shows a marked predilection for women, with the incidence rate approximately 8 times higher in women than in men.

  • Patient Profile: The majority of patients are young or middle-aged women (within childbearing age)
  • Location: FNH lesions appear more frequently in the right hepatic lobe.
  • Hormonal Association: It is weakly associated with the use of oral contraceptives.

👩‍⚕️ Clinical Presentation of Focal Nodular Hyperplasia (FNH)

Most cases of FNH are discovered incidentally (asymptomatic) during imaging for other reasons.

  • Symptomatic Cases: When symptomatic, the most common complaints include recent or chronic abdominal pain, which accounted for 57.7% of cases in a review.
  • Case Example: The 31-year-old female patient presented with intermittent abdominal pain that started in her lower back and radiated throughout her abdomen, concentrating in the epigastrium. She also reported recurrent nausea and vomiting over the preceding few months.

🖼️ Imaging Features of Focal Nodular Hyperplasia (FNH)

The diagnosis of FNH is often made confidently through characteristic imaging findings on Computed Tomography (CT) and Magnetic Resonance Imaging (MRI).

CT Findings

  • Appearance: CT scans typically show a well-circumscribed, iso-attenuating lesion with a central scar of reduced attenuation.

  • Case Image: The contrast-enhanced abdominal CT in the case study demonstrated a hepatic lesion.

Figure 1 Abdomen Axial c+ portal venous phase

Figure 2 Abdomen coronal c+ portal venous phase


Figure 3 Abdomen sagittal c+ portal venous phase

MRI Findings (The Gold Standard)

Contrast-enhanced MRI is the most suitable study for further characterization of soft-tissue lesions due to its highest sensitivity and specificity.
  • T1/T2 Weighting: The mass is typically mildly hypo-intense on T1 and iso-intense on T2 imaging.  
  • Central Scar: The associated central scar is classically T2 hyper-intense and T1 hypo-intense.

  • Contrast Enhancement: FNH shows intense initial, relatively homogeneous arterial enhancement. Crucially, the lesion fades to iso-intensity relative to the background liver on delayed/portal venous phase images. The central scar typically shows delayed, faint enhancement.

  • Eovist (Gadoxetate disodium): Using the contrast agent Eovist further increases the specificity because FNH takes up the contrast during the hepatobiliary delayed phase, while other common lesions often do not.

Figure 4 MRI
The mass in segments 4/1 is seen as a well-encapsulated mass (approximately 4.7 X 3.5 X 4.2 cm) showing features consistent with FNH: intense initial enhancement fading to iso-intensity on delayed images, and an associated central scar that is T2 hyper-intense/T1 hypo-intense and shows faint delayed enhancement. The sensitivity and specificity of this diagnosis approach 100% with contrast-enhanced MRI. 

Figure 5 Example of Focal nodular hyperplasia [Image showing a side-by-side comparison of an anatomical diagram and a CT scan of FNH, both highlighting the central scar (black arrow) and the well-circumscribed nature of the lesion (yellow circle, white arrow)]

🩺 Differential Diagnosis (DDx) and Definitive Diagnosis

The primary goal of imaging is to distinguish FNH from other common liver masses, especially those with malignant potential or a risk of hemorrhage.

Definitive Diagnosis: Focal Nodular Hyperplasia (FNH). The presence of a central scar, intense arterial enhancement, and fading to iso-intensity on delayed phases in a young woman is highly characteristic.

💊 Treatment and Prognosis

The prognosis for patients with FNH is excellent as it is a benign lesion with no malignant potential.
  • Management: Management is generally conservative. 
  • Treatment: Surgical resection is the final treatment option reserved for symptomatic patients. Since most patients are asymptomatic, regular follow-up imaging is often sufficient.

Quiz

Question 1 ( Most Common Benign Lesion) What is the most common benign liver lesion in adults? 

(1) Hemangioma/venous malformation 

(2) Focal nodular hyperplasia (FNH) 

(3) Adenoma 

(4) Angiomyolipoma

Answer: (1) Hemangioma/venous malformation. Explanation: While Focal Nodular Hyperplasia (FNH) is a very common benign liver lesion, the Hemangioma (venous malformation) is the most common benign lesion found in the adult liver.

Question 2 (Best Imaging Modality) Following the initial detection of a solid liver lesion on a contrast-enhanced CT, which study is the most suitable for subsequent evaluation and definitive characterization?

(1) Complete abdominal ultrasound 

(2) Focused right upper quadrant ultrasound 

(3) Contrast-enhanced MRI abdomen 

(4) Noncontrast MRI abdomen 

Answer: (3) Contrast-enhanced MRI abdomen. Explanation: Contrast-enhanced MRI provides the highest sensitivity and characterization for evaluating soft tissue lesions of the liver, which is essential for differentiating FNH from other lesions like adenoma or hepatocellular carcinoma.

Question 3 (FNH Key Features and Malignancy) Which statement regarding Focal Nodular Hyperplasia (FNH) is TRUE?

(1) FNH has a recognized potential for malignant transformation. 

(2) FNH lesions typically require surgical resection in all cases. 

(3) The classical finding on MRI is a central scar that is T2 hypo-intense/T1 hyper-intense. 

(4) FNH is a common benign disease of the liver without recognized malignant potential. 

Answer: (4) FNH is a common benign disease of the liver without recognized malignant potential. 

Explanation:

  • (1) is False. FNH is a benign condition without malignant potential.

  • (2) is False. Management is conservative, and surgical resection is reserved for symptomatic patients.

  • (3) is False. The central scar is classically T2 hyper-intense and T1 hypo-intense.

Reference

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[2] C. Balabaud et al., "Focal nodular hyperplasia and hepatocellular adenoma around the world viewed through the scope of the immunopathological classification," Int. J. Hepatol., vol. 2013, 268625, 2013. doi: 10.1155/2013/268625.

[3] S. Hamad, C. E. Willyard, and S. Mukherjee, "Focal nodular hyperplasia," StatPearls Publishing, Treasure Island, FL, 2020. [Online]. Available: https://www.ncbi.nlm.nih.gov/books/NBK560868/.

[4] A. P. Navarro et al., "Focal nodular hyperplasia: A review of current indications for and outcomes of hepatic resection," HPB (Oxford), vol. 16, no. 6, pp. 503–511, 2014.

[5] B. N. Nguyen et al., "Focal nodular hyperplasia of the liver: A comprehensive pathologic study of 305 lesions and recognition of new histologic forms," Am. J. Surg. Pathol., vol. 23, no. 12, pp. 1441–1454, Dec. 1999. doi: 10.1097/00000478-199912000-00001.

[6] C. H. Suh et al., "The diagnostic value of Gd-EOB-DTPA-MRI for the diagnosis of focal nodular hyperplasia: a systematic review and meta-analysis," Eur. Radiol., vol. 25, pp. 950–960, 2015. doi: 10.1007/s00330-014-3499-9.

[7] S. M. Hussain et al., "Focal Nodular Hyperplasia: Findings at State-of-the-Art MR Imaging, US, CT, and Pathologic Analysis," Radiology, vol. 233, no. 1, pp. 1–13, 2004.

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