Focal nodular hyperplasia
Updates to Article Attributes
Focal nodular hyperplasia (FNH) is a benign tumour-like mass of the liver, second only to haemangiomas in frequency. It has characteristic radiographic features but multi-modality imaging may be required in atypical cases. FNH are usually treated conservatively.
Epidemiology
FNH is most frequently found in young to middle aged adults, with a strong female predilection 3-4; ~15% (range 10-20%) occur in men 7. Additionally, exogenous oestrogens have been shown to increase the size of these masses 4. Solitary occurrence is more common.
Clinical presentation
These masses are either found incidentally on imaging or present due to mass effect with right upper quadrant pain in 20% 5. Unlike hepatic adenomas, FNH are only rarely complicated by spontaneous rupture and haemorrhage 1,4.
Associations
Association with other benign lesions is seen in up to 23%, including adenomas and haemangiomas 8
- hereditary haemorrhagic telangiectasia
- arteriovenous malformations (AVM)
- anomalous venous drainage
- hepatic haemangioma 6
- congenital absence of portal vein/portal vein atresia
- Budd-Chiari syndrome
- portal shunts
- idiopathic portal hypertension
- portal or pulmonary hypertension 7
Pathology
The origin of FNH is thought to be due to hyperplastic growth of normal hepatocytes with a malformed biliary draining system. It is also thought to be in response to a pre-existent arteriovenous malformation 1,4. The arterial supply is derived from the hepatic artery whereas the venous drainage is into the hepatic veins. FNH does not contain portal venous supply9.
FNH is divided into two types 4:
- typical: 80%
- atypical: 20%
Typical FNH
Macroscopically, typical lesions demonstrate a tumour which is often quite large with well circumscribed margins. A prominent central scar is usually noted with radiating fibrous septae: <50% of cases 7. A large central artery is usually present with spoke-wheel like centrifugal flow 3-4 (no portal veins).
Histologically the lesion is multinodular, composed of nearly normal hepatocytes arranged in 1-2 cell thick plates. Bile ductules are usually found at the interface between hepatocytes and fibrous regions 1-2. Kupffer cells are present 4,7.
There is essentially no malignant potential 1.
Atypical FNH
An atypical FNH essentially refers to a lesion which lacks the central scar and central artery, and is thus harder to distinguish from other lesions on gross inspection and imaging 4.
Atypical features also include pseudocapsule, lesion heterogeneity (more commonly seen in adenoma), non enhancement of the central scar and intralesional fat 6.
Nodules can grow and disappear and new nodules can appear even after resection 7.
Variants
Some authors also describe division of atypical FNH into several variants which include 8:
- telangiectatic variant
- mixed hyperplastic and adenomatous variant
- lesions with large cell hepatocellular atypia
Radiographic features
As FNH is usually treated conservatively, accurate imaging is essential in preventing unnecessary intervention.
It should be noted that up to 20% of patients with an FNH will have multiple lesions 4 and a further 23% will have haemangiomas 4.
Ultrasound
The echogenicity of both FNH (and its scar) is variable and it may be difficult to detect on ultrasound. Some lesions are well marginated and easily seen whereas other are isoechoic with surrounding liver. Detectable lesions characteristically will demonstrate a central scar with displacement of peripheral vasculature on colour Doppler examination, however these findings are seen in only 20% of cases 4.
- contrast-enhanced ultrasound 14:
- arterial phase
- FNH will enhance relative to background liver
- prominent feeding vessel may be seen
- portal venous phase
- centrifugal filling (opposite to haemangioma and adenoma)
- sustained enhancement in the portal venous phase
- unenhanced scar may be present
- arterial phase
CT
A multi-phase scan is ideal, commonly comprising 4:
- non-contrast
- arterial (25-35 second delay)
- portal venous (60-70 second delay)
- delayed (5-10 minute delay)
On the non contrast series, the lesion is usually hypo- or isoattenuatung, but may appear hyperattenuating if the rest of the liver is fatty. A hypoattenuating central scar can be seen in up to 60% of lesions >3 cm in size 4.
FNH demonstrates bright arterial contrast enhancement except for the central scar which remains hypoattenuating 4. Enlarged central arteries may be seen.
In the portal venous phase the lesion becomes isoattenuating to liver.
The scar demonstrates enhancement on delayed scans in up to 80% of cases 4
MRI
MRI is both sensitive (70%) and specific (98%).
See: liver MRI protocol
-
T1
- iso to moderately hypointense
- hypointense central scar
-
T2
- iso to somewhat hyperintense
- hyperintense central scar
-
contrast studies
-
T1 C+ (Gd)
- intense early arterial phase enhancement, similar to CT
- central scar retains contrast on delayed scans 13
- isointense to liver on portal venous phase 10-12
-
T1 C+ (Eovist)
- early arterial enhancement
- enhancement persists into delayed phases 11
- fades toward background liver intensity on the hepatobiliary phase, with a small amount of enhancement remaining (c.f. adenomas which appear hypointense relative to liver on hepatobiliary phase)
-
T2* C+ (reticuloendothelial agent: SPIO)
- hypointense mass as a result of suceptibility signal loss due to uptake by Kupffer cells
-
T1 C+ (Gd)
Nuclear medicine
The presence of Kupffer cells in FNH allows these lesions to take up technetium (Tc) 99m sulphur colloid. P\A positive scans is seen in 80% of lesions, and is helpful in distinguishing them from hepatic adenomas, HCC and hepatic metastases which do not contain Kupffer cells 4.
Treatment and prognosis
FNH is benign, with no malignant potential and a very small risk of complication (rupture, haemorrhage) and thus are usually treated conservatively 1.
Differential diagnosis
General imaging differential considerations include:
- hepatic adenoma
- hepatocellular carcinoma (HCC)
- fibrolamellar HCC
- hypervascular hepatic metastasis(es)
- hepatic haemangioma
Practical points
For all practical purposes, don'tdo not call FNH in a cirrhotic liverref required.
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