Imaging features of diffuse hepatic steatosis.
Ultrasound:
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CT:
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MRI:
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Hyper-echoic liver.(Fig1)
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Hypo-attenuation of the liver parenchyma.
(Fig1)
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T1: Increased signal.
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The renal cortex appears hypo-echoic relative to the liver.
(Fig2)
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Non-contrast CT: attenuation of the liver is >10Hounsfield units (HU) less than that of the spleen
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T2: Mild increase in signal intensity less so than on T1.
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Poor delineation of intra-hepatic echotexture.
(Fig1)
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Contrast enhanced CT: Attenuation is >40HU less than that of the spleen.
(Fig3)
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Opposed phase: Decreased signal intensity.
In-phase: Increased signal intensity.
(Fig7)
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Poor visualization of the deep portions of the liver parenchyma and diaphragm.
(Fig1)
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>15% signal drop out in the opposed phase imaging.
(Fig5)
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Imaging patterns of focal fatty change and common locations.
Focal fatty deposition.
Focal fat deposition characteristically occurs in specific areas.
These include adjacent to the gallbladder fossa,
the porta hepatis,
and the falciform ligament.
The diagnosis of focal fatty deposition is more difficult than diffuse fatty change and can commonly be misinterpreted as a sinister focal liver lesion.
(Fig5&6)
Focal fat sparing.
Typically occurs in the same specific areas as focal fatty deposition.
And can again often be misinterpreted as focal liver lesion.
(Fig5)
Multifocal deposition.
Multiple areas of fatty infiltration are scattered throughout the liver parenchyma.
Correct diagnosis is again difficult.
(Fig7)
Perivascular fat deposition.
This is characterized by halos of fat surrounding the hepatic veins,
portal veins,
or both hepatic and portal veins.
An unequivocal signal intensity loss on opposed-phase images in comparison with in-phase images and the lack of mass effect in the surrounding vessels is indicative of perivascular fat deposition.
The Impact of Chemotherapy.
Chemotherapeutic agents can induce hepatic steatosis with specific regimens,
and is associated with a wide range of chemotherapeutic agents.
(9)(Fig 8)
This can occur relatively rapidly,
but often resolves after therapy is discontinued.
(Fig15&16) Recognition of the specific patterns of focal fatty change can allow the radiologist to intervene and prevent over and under treatment.
Difficulties in diagnosing metastasis.
The diagnosis of diffuse hepatic steatosis in the liver is straightforward.
However differentiation of fat deposition in the liver from a low attenuating metastatic lesion or fat containing malignancy can be more difficult.
Imaging pitfalls associated with heptic steatosis include differentiating a focus of geographic fatty change from metastasis (Fig13,14&15) and focal fat sparing from an enhanced tumor.
(Fig12)
A threshold attenuation value of less than 40 Hu is not specific for fat deposition for example ischemic or mucinous metastasis or abscesses may manifest low attenuation values (10,11)(Fig15)
Also focal fatty sparing in a liver with diffuse fat deposition may mimic an enhanced hypervascular tumour at contrast enhance CT.
Therefore Mri chemical shift Gradient Echo imaging is often required to further evaluate.
(Fig13,14,15&16)