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| Discussion |
A 16 year-old-girl presented with complaints of a lump in the epigastric
region since five years which progressively increased in size. There was no history
of vomiting, hematemesis, malena, jaundice or fever. On examination, the lump
was firm to hard on palpation, moving with respiration and was palpable 10cms
below the costal margin. The patient's vital parameters were normal; the serum
alpha fetoproteins were within normal limits.
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| Fig. 1 |
Fig. 2 |
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Fig.
3 | Fig.
4 |
arising from the left lobe of the liver with a large exophytic component.
It showed a central scar, which appeared hyperechoic with evidence of calcification
within it. Multiple septe were seen radiating from this central scar towards the
periphery giving it a pseudolobular appearance. On colour Doppler, the lesion
showed moderate vascularity. The scar and its septe did not show any vascularity.
Triple phase CT scan of the abdomen showed gross hepatomegaly with a large
mass lesion involving the left lobe of the liver extending into the right lobe
with an exophytic component.
On plain scan, the lesion showed a variegated
appearance with hyper and hypodense components within. A central stellate scar
was seen with the foci of calcification with fat components within.
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Fig.
5 | Fig.
6 | |
Images
obtained during the arterial phase showed hypertrophy of the common hepatic artery.
No obvious neovascularity was detected. The main portal vein and its left branch
were displaced laterally and inferiorly.
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Fig.
7 | Fig.
8 | |
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Fig.
9 | Fig.
10 | |
A
delayed scan showed a non-enhancing scar with subtle enhancement of the capsule
of the tumor.
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Fig.
11 |
An
MR scan was done for further characterization of the tumor.The mass was predominantly
iso to hypointense on gradient T1W images. Chemical shift images confirmed fat
intensity within the mass. On T2W image, mass appeared hypointense whereas the
scar was hyperintense.
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Fig.
12 | Fig.
13 | |
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Fig.
14 | Fig.
15 | |
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Fig.
16 | ||
Films
obtained during the arterial phase after intravenous contrast administration showed
heterogenous enhancement of the mass with a non-enhancing scar. The capsule was
well demonstrated on delayed images. There was no dilatation of biliary radicals.
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Fig.
17 | Fig.
18 | |
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Fig.
19 | ||
A radiological diagnosis of an atypical focal nodular hyperplasia was made.
A CT guided biopsy was performed. Histopathological diagnosis was consistent
with focal nodular hyperplasia.
DISCUSSION:
Focal Nodular Hyperplasia
(FNH) is the second most common benign liver tumor after hemangioma and has a
reported prevalence of 0.9%. The male-to-female ratio is 1:8, and the tumor occurs
in relatively young patients.
FNH is believed to occur as a result of a localized hepatocyte response to
an underlying congenital arteriovenous malformation. FNH is a hyperplastic process
in which all the normal constituents of the liver are present but in an abnormally
organized pattern. Oral contraceptive use is not responsible for the development
of FNH, but it probably stimulates its growth.
FNH is often an incidental
finding at imaging. Distinction between FNH and other hypervascular liver lesions
such as hepatocellular adenoma, hepatocellular carcinoma (HCC), and hypervascular
metastases is critical to ensure proper treatment. FNH is asymptomatic in most
patients, and in such cases no treatment is necessary. A small minority (10-15%)
may present with vague abdominal symptoms from mass effect, a palpable mass, or
hepatomegaly.
Pathology - The gross appearance of classic FNH consists of lobulated contours
and parenchyma that is composed of nodules surrounded by radiating fibrous septa
originating from a central scar. The central scar contains malformed vascular
structures.
On Imaging studies, typical and atypical lesions can
often be distinguished on the basis of morphology. Typical FNH can be diagnosed
with confidence at CT or MR imaging. Atypical FNH may appear as a large lesion,
which is sometimes multiple in location. The tumor may show less intense enhancement,
unusual appearance or nonenhancement of the central scar and a pseudocapsular
enhancement on delayed images. In such cases, histopathological study may be required
to confirm the diagnosis.
On MRI, typically, FNH is iso- or hypointense
on T1W images, is slightly hyper- or isointense on T2W images, and has a hyperintense
central scar on T2W images. FNH demonstrates intense homogeneous enhancement during
the arterial phase of gadolinium-enhanced imaging and enhancement of the central
scar during later phases.
On
CT - The most reliable signs of FNH are homogeneous bright enhancement and a central
scar. Other common features of FNH are smooth (nonlobulated) contour, ill-defined
margins, and a subcapsular location. Calcification is a rare finding in FNH.
FNH
does not have a tumor capsule, although the pseudocapsule surrounding some FNH
lesions may be quite prominent. The pseudocapsule typically shows high signal
intensity on T2W images and may show enhancement on delayed contrast-enhanced
images. On the contrary, tumor capsule which is a characteristic feature of HCC
(seen in 60% - 80%) has low signal intensity on both T1- and T2-weighted images;
it shows persistent enhancement on delayed contrast-enhanced images.
A central scar is present at imaging in most patients (50%) with FNH. However,
it is not a specific finding of FNH and can be seen in a variety of other focal
liver lesions such as giant hemangiomas and HCC's. The central scar in FNH is
typically high in signal intensity on T2W images and low in signal intensity on
T1W images. It shows visible enhancement on delayed contrast-enhanced images.
The central scar in giant hemangiomas is typically larger and brighter on T2-weighted
images. In addition, the lesions have homogeneous high signal intensity on T2-weighted
images and show peripheral nodular enhancement in most cases. Some HCCs may contain
a central scar, which shows low signal intensity on T2- and T1-weighted images
and does not enhance much on contrast-enhanced images.
While adenomas are also most common in women of reproductive age, adenomas are
more likely than FNH to contain areas of heterogeneity, fat, necrosis, hemorrhage,
and calcification. Adenomas usually enhance less brightly and less homogeneously
than FNH.
Metastases, as compared with FNH, are more often multiple, heterogeneous,
and less likely to be isoattenuating to liver on nonenhanced, portal venous phase,
and delayed CT scans.
Most hemangiomas are easily diagnosed with CT due
to the characteristic nodular, peripheral, and progressive enhancement. Small
hemangiomas may be uniformly hyperattenuating on arterial phase but are usually
similar to blood pool attenuation on all phases of enhanced and nonenhanced CT,
unlike FNH.
No treatment is necessary in most of the cases as it is often
asymptomatic. Some patients who present with symptoms due to mass effect or hepatomegaly
may require treatment such as transarterial embolization or surgical resection.
Although FNH usually has no clinical significance, recognition of the
radiologic characteristics of FNH is important to avoid unnecessary surgery, biopsy,
and follow-up imaging. Malignant transformation of FNH has not been reported.