Computed Tomography:
The main advantage of CT scans is to allow a more accurate detection and a better characterization of focal hepatic lesions.
(3)
The comparison of the HCA relative to the liver depends on the composition of the tumor and of the liver as well as on the phase of contrast material enhancement.
Using a 16-slice helical CT, non-enhanced images are the first to be obtained.
Then,
after the injection of intravenous non ionic contrast (120-150ml at a rate of 3-5mL/s with a 25 to 30s delay) the arterial phase images are obtained.
After a 70-80 delay,
a scan is made for the portal venous phase.
Imaging findings of HCA in CT:
- Well marginated, nonlobulated mass,
that sometimes can be encapsulated and is rarely calcified.
(Fig.1)
- Homogeneous enhancement in the hepatic arterial phase.(Fig.
2) Typically isoattenuating but sometimes mildly hypoattenuating relative to normal liver on unenhanced,
portal venous–phase and delayed-phase images.(6) (Fig.3)
- Can be a hypoattenuating mass if the presence of intratumoral fat is considerable.
(Fig.1) If it`s surrounded by a fatty liver it appears hyperattenuating on all contrast phases and unenhanced images.
- Necrosis or old hemorrhage is usually seen as a heterogeneous, hypoattenuating area within the tumor.
- Larger hepatocellular adenomas may be more heterogeneous than smaller lesions,
and their CT appearance is less specific.
Magnetic Resonance Imaging:
With this technique the detection of fat and hemorrhage is usually more sensitive and accurate,
leading to a better understanding of the composition of the focal hepatic lesions.(3)
A 1,5 tesla MRI was used to perform the exams.
Protocol included a sagittal gradient echo, sagittal and axial T1 post gadolinium injection.
Imaging findings of HCA in MRI:
- From hyperintense to mildly hipointense relative to the liver tissue on T1-weighted images.
This heterogeneous appearance results from areas of high intensity due to fat and acute hemorrhage and low signal-intensity area corresponding to necrosis or old hemorrhage or calcifications.
(3) (Fig.4)
- On T2-weighted images hepatocellular adenomas are predominantly hyperintense relative to liver. Although in the presence of necrosis and hemorrhage they can be heterogeneous with hyper and hypo-attenuating signal.(Fig.4 and 5)
- Dynamic postgadolinium show intense arterial phase enhancement with isointensity on portal phase and delayed images.
- A pseudocapsule (rim) can be seen in some patients as a peripheral zone of low signal intensity on both T1 and T2 weighted images (8).(Fig.6)
- HCA don’t have a central scar so if a central scar enhances after gadolinium is administered,
the diagnosis of FNH is strongly favored.
A central scar has never been reported in hepatic adenomas.
- With the injection of a hepatocellular-specific contrast agent,
gadolinium benzyloxypropionictetraacetate (Gd-BOPTA) there is usually no substantial uptake.
These imaging characteristics are still not enough to solely give the final diagnosis of Hepatocellular Adenoma.
It is necessary to correlate these characteristics with the findings of a histological evaluation through liver biopsy (Fig.7) and eventually resection of the tumor.
(1) Only then can we make the final diagnosis of Hepatocellular Adenoma.
Differential diagnosis:
- Focal Nodular Hyperplasia (7)
o No malignant degeneration or hemorrhage,
o On T2 weighted images central scar is typically
hyperintense.
- Hepatocellular Carcinoma (7)
o Similar imaging features as hepatocellular adenoma,
o Biliary,
nodal invasion and metastases establish
the malignancy.
- Fibrolamellar Hepatocellular Carcinoma (7)
o Large, lobulated mass scar and septa,
o Heterogeneous on all imaging.
- Hipervascular Metastases (7)
o Hypointense on T1 weighted images and markedly
hyperintense on T2 weighted images,
o Typically in large numbers and in the presence of primary tumor (breast,
thyroid,
kidney and endocrine)
Histopathology:
HCA are constituted by large plates of cells closely resembling normal hepatocytes,
with the plates being separated by dilated sinusoids.
(Fig.8) Adenomas lack a portal venous supply and are fed solely by peripheral arterial feeding vessels.(9) The extensive sinusoids and feeding arteries constitute the hypervascular nature of hepatocellular adenoma.
A fibrous capsule is uncommon and can be complete or incomplete. Adenoma cells are larger than normal hepatocytes and contain large amounts of glycogen and lipid. Intra- and intercellular lipid uncommonly manifests as macroscopic fat deposits within the tumor.(9)