Focal Nodular Hyperplasia

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DEFINITION
A hyperplastic reaction to an arterial malformation that induces a (benign) liver mass.

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EPIDEMIOLOGY

Incidence
2nd most common liver lesion.
Age
30-50 peak age
Gender
Female predilection

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AETIOLOGY

Pathogenesis


Sieve

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BIOLOGICAL BEHAVIOUR

Pathophysiology
A hyperplastic reaction to an arterial malformation
- i.e. arterial malformation --> hyperperfusion of liver parenchyma --> hepatocellular hyperplasia
Supported by evidence showing polyclonal regenerative process.
Not related to oestrogen administration.

Pathology
Macroscopically, a well-circumscribed, unencapsulated lesion, with a central fibrous scar.
Microscopically, normal hepatocytes arranged in nodules with fibrous septa, originating from a central scar.
Majority solitary but 20-30% have multiple lesions.

Natural history
Malignant transformation has not been reported.

Complications
Can cause pressure on adjacent organs.
Pedunculated lesions can torse on their pedicle, causing pain.

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MANIFESTATIONS

Symptoms
Most lesions are asymptomatic
And are picked up incidentally on imaging.

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INVESTIGATIONS

Biochemistry
LFTs generally normal, but ALP and GGT rise possible.

Imaging
Central scar is characteristic
- but not specific, as also seen in fibrolamellar HCC, hepatic adenomas, and mets.
CT
Hypodense or isodense on precontrast CT
These are vascular lesions, so fill in rapidly with IV contrast
- then becomes well demarcated; central hypodense scar.
- then washes out during portal venous phase
- then becomes isodense on the delayed phase.
- but(!) central scar can gradually become denser with delay due to slower contrast uptake.
MRI
Isointense or hypointense on T1 weighted images
Isointense or slightly hyperintense on T2 images.
Gadolinium results in hyperintensity during the portal venous phase.
- isointensity during portal venous phase but central scar becomes hyperintense on delayed imaging.
Most studies demonstrate higher sensitivity and specificity for MRI than CT or USS.
- if still uncertain, sulphur colloid scan can help.
- taken up by Kupffer cells, whereas hepatic adenomas do not.

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MANAGEMENT

No treatment when asymptomatic.
No evidence to avoid pregnancy or discontinue OCP
Follow up unnecessary.

Operative
Only indicated if symptomatic
Taking a margin of normal parenchyma is safer than enucleation.

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REFERENCES
Cameron 10th

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