Full story fatty liver imaging Dr Ahmed Esawy

Full Story Fatty Liver
Imaging
Dr. Ahmed Esawy
MBBS M.Sc MD

Introduction
The image-based diagnosis of fatty
liver usually is straightforward, but
fat accumulation may be manifested
with unusual structural patterns that
mimic neoplastic, inflammatory, or
vascular conditions.
Leading to :
Unnecessary diagnosis test and Invasive procedure

Table of content
• Risk Factors and Pathophysiologic
Features
• Imaging-based Diagnosis of Fatty
Liver
• Patterns of Fat Deposition
• Differential Diagnosis
• Pitfalls

Risk Factors and
Pathophysiologic Features
Histologically
Fatty liver: Triglyceride
accumulation within the
cytoplasm of hepatocytes.
Term ―fatty infiltration of the liver‖ is misleading because
fat deposition is characterized by accumulation of
discrete triglyceride droplets in hepatocytes and rarely,
in other cell types. The term fatty liver is more accurate.

Conditions Associated with Fatty Liver

Pathophysiologic
Features
Triglyceride accumulation (steatosis)
within hepatocytes by altering
the hepatocellular lipid metabolism,
in particular, by causing
defects in free fatty acid metabolic
pathways.

Pathophysiologic
Features
• Hepatocytes in the center of the lobule
(near the central vein) are tend to
accumulate lipid earlier than periphery.
• In advanced cases, there is diffuse,
relatively homogeneous involvement of
the entire lobule.
• Steatosis may progress to steatohepatitis
( with inflammation, cell injury, or fibrosis
accompanying steatosis) and cirrhosis.

Pathophysiologic
Features
• To grade steatosis, pathologist
visually estimate the fraction of
hepatocytes that contain fat droplets.
• 0%, 1-5%, 6-33%, 34-66%, ≥67%.
• Size of fat droplets is not considered.

Natural history of fatty liver
disease

Once fatty liver is found ,
look for for causes. If no
cause is found labelled as
NAFLD nonalcoholic fatty
liver disease. This affects
10-20% of population.
Those with normal liver
enzymes can be managed
with reduction in weight
and lifestyle modification.
Those with
persistent
elevated liver
enzymes are
called NASH
Nonalcoholic
steatohepatitis.

Prevalence of Fatty
Liver
• General population about 15%.
• Higher in
–40% of consume large quanities of
alcohol (>60g /day)
–50% of Hyperlipidemia
–75% of Obesity (BMI> 30 kg/m2)
–95% of Both obesity and high alcohol
consumption

Imaging-based
Diagnosis of Fatty Liver
• Diagnosis at US
• Diagnosis at CT
• Diagnosis at MR Imaging
• Elastography
• Contrast enhanced
ultrasound

Diagnosis at US
Normal Liver
• Echogenicity of the
normal liver equals or
minimally exceeds that
of the renal cortex or
spleen.
• Intrahepatic vessels are
sharply demarcated
• Posterior aspects of the
liver are well depicted
Fatty liver
• Liver echogenicity
exceeds that of renal
cortex and spleen
• Poor delineation of the
intrahepatic architecture
• Loss of definition of
diaphragm

Liver Pathology (Diffuse Diseases).
 Fatty Liver
 • Mild (early stage)
 Minimal increase in liver
echogenicity
 Intrahepatic vessels and diaphragm
well visualized.
 • Moderate (mid stage)
 Moderate increase in liver
echogenicity
 Intrahepatic vessels and diaphragm
suboptimally visualized.
 • Severe (late stage)
 Significant increase in liver
echogenicity
 Poor visualization of posterior
aspect of liver
 Poor or nonvisualization of
intrahepatic vessels and diaphragm
.
 Focal fat infiltration
 Hyperechoic area within an otherwise
normal liver
 commonly seen in right lobe and may
resolve over time .
 Focal fat sparing
 Area of normal liver within fatty liver;
 commonly seen anterior to portal vein
and Gallbladder.
 Focal fat infiltration and sparing
may mimic liver tumor

Does grade 3 fatty liver
means progression to
cirrhosis..?
•NO. Not necessarily
• it is a rough estimate
for fat in liver , that`s all

Sonographic features of normal
liver (A) show same echogenicity
as the kidney while fatty liver
(B) shows increased
echogenicity compared with the
kidney.

Diagnosis of fatty liver based on ultrasound evaluation.
1 – parenchymal hyperechogenicity, 2 – intensified
attenuation,
3 – poorly visible vessels, 4 – focal hyposteatosis.
Presence of all four signs leads to diagnosis of fatty liver

Criteria for fatty liver on USG
• Liver echogenicity exceeds
that of right kidney and
spleen.
• There is beam attenuation.

Fatty liver
• Posterior sound
attenuation.
• Enlarged liver.
• Tend to have fine
homogeneous
echotexture.

Normal Liver Fatty Liver
To avoid false-positive interpretations, fatty liver should
not be considered present if only one or two of these
criteria are fulfilled

What is grading of fatty liver on USG
Grade
1
Grade
2
Grade
3

• grade I: increased hepatic echogenicity with
visible periportal and diaphragmatic echogenicity
• grade II: increased hepatic echogenicity with
imperceptible periportal echogenicity, without
obscuration of diaphragm
• grade III: increased hepatic echogenicity with
imperceptible periportal echogenicity
and obscuration of diaphragm
Grading of fatty liver

Severe fatty infiltration of the liver. A
longitudinal image showing increased
echogenicity of the liver in the anterior
segment .The posterior segment is
hypoechoic because of poor penetration of
the beam. The diaphragm (arrow) is poorly
demonstrated and the intrahepatic vessels
are not seen.
Mild fatty infiltration of the liver. A
longitudinal image showing generalized
increased echogenicity of the liver. Note that
the diaphragm (black arrow) and section of an
intrahepatic vessel (white arrow) are well
visualized. Right kidney (RK) is posterior to
the liver.

Can not be detected on USG at present
Biopsy is recommended to assess
inflammation and fibrosis.

Two new techniques
promise to fill this gap

Fatty fibrotic pattern
• Increased echogenicity of
liver parenchyma.
• Decreased definitions of PV
walls.
• Echotexture
- Homogeneous (fine)
- Heterogeneous (coarse).
• Posterior sound attenuation.
• Causes: fatty infiltration,
chronic hepatitis, cirrhosis,
acute alcoholic hepatitis.

Fatty fibrotic pattern
Echotexture
• homogeneous • heterogeneous

Diagnosis at CT
Normal Liver
• The normal liver has
slightly greater
attenuation than the
spleen and blood.
• Intrahepatic vessels are
visible as
hypoattenuated
structures
Fatty liver
• Unenhanced CT
• Attenuation of the liver is
at least 10 HU less than
that of the spleen or
attenuation of fatty liver
is less than 40 HU
• In severe cases,
intrahepatic vessels may
appear hyperattenuated
relative to fat-containing
liver tissue.

Fatty liver CT without contrast demonstrates liver
41 HU, spleen 56 HU.

Fatty Liver CT with contrast in 33-year-old female
demonstrates liver attenuation 36 HU.

Normal Liver Fatty Liver
• At enhanced CT, the comparison of liver and
spleen attenuation value is not reliable.
• Fatty liver can be diagnosed at contrast-
enhanced CT if absolute attenuation is less than 40
HU, but this threshold has limited sensitivity.

• Normal appearance of the liver at unenhanced CT. The
attenuation of the liver (66 HU) is slightly higher than that
of the spleen (56 HU), and intrahepatic vessels (v) appear
hypoattenuated in comparison with the liver.

• Diffuse fat accumulation in the liver at un-enhanced CT. The
attenuation of the liver (15 HU) is markedly lower than that of
the spleen (40 HU). Intrahepatic vessels (v) also appear
hyperattenuated in comparison with the liver.

• Then if the liver is < 40 HU, is that
specific for liver steatosis?
• a. No. Ischemic or mucinous
metastases,or abscesses can have
this attenuation. Clinical, laboratory,
and other imaging features need
consideration.

Lipid quantification can be performed by the following
methods:
a. Hepatic attenuation measurement i. A value of 40 HU
is reported to represent fatty change of approximately
30%.
b. Hepatic attenuation index i. A ratio of hepatic HU to
splenic HU less than 0.8 is reported as highly specific for
moderate to severe (>30%) macrovesicular steatosis.
c. Hepatic attenuation difference at dual-energy CT
note, in review, that while there is a paucity of literature
to validate its use, an increase in fatty content associates
with decreased HU at low energy; when the energy level
increases, the fat attenuation increases

Diagnosis at MR
Imaging
Normal Liver
The signal intensity of the
normal liver
parenchyma is similar
on in-phase and
opposed-phase images
Fatty liver
The signal intensity loss on
opposed-phase images
in comparison with in-
phase images.
Chemical shift gradient-echo(GRE) imaging with
in-phase and opposed-phase acquisitions is the most
widely used MR imaging technique for the assessment
of fatty liver.

Chemical shift gradient-
echo(GRE) imaging with
in-phase and opposed-phase
Normal Liver
The signal
intensity of
the normal
liver
parenchyma
is similar on
in-phase and
opposed-
phase
images

Chemical shift gradient-
echo(GRE) imaging with
in-phase and opposed-phase
Fatty liver
The signal
intensity loss
on opposed-
phase
images in
comparison
with in-phase
images.

Chemical shift gradient-echo(GRE) imaging
opposed-phase in-phase

T1 in-phase MRI (left) and T1 out-of-phase MRI (right) shows liver
signal loss on out-of-phase image

T1 in-phase MRI (left) and T1 out-of-phase MRI (right) of 55-year-old male
shows diffuse liver signal loss on out-of-phase image.

Potential pitfalls in Opposed-
phase T1 include:
• 1. The presence of liver iron, which
can cause signal intensity loss on in
phase images.
• 2. Fat fractions >50%, which cannot
be reliably assessed
• 3. Fat is spectrally complex.

T2 weighted imaging
with (bottom left),
and without (bottom
right), fat saturation
can be
used to detect
steatosis. When no
fat-saturation is
used, the liver is
relatively bright
compared to the
spleen (arrow).
When steatosis is
present, the signal
intensity of the liver
drops because the
fat-saturation pulse
suppresses the
signal from fat within
the liver
Note the relative signal intensity of fat relative to the spleen in the fat-saturated image.
IOP imaging (top row) demonstrates marked signal dropout on opposed-phase
imaging indicating the presence of steatosis.

Accuracy for Detection and
Grading of Fat Deposition
Sensitivity Specificity
• US 60-100% 77-95%
• NECT 43-95% 90%
• Chemical shift GRE MRI
81% 100%

Patterns of Fat Deposition
• Diffuse Deposition.
• Focal Deposition and Focal
Sparing.
• Multifocal Deposition.
• Perivascular Deposition.
• Subcapsular Deposition.

Diffuse Deposition
• Diffuse fat deposition in the liver is the
most frequently encountered pattern.
• Liver involvement usually is
homogeneous.
• The image interpretation is
straightforward if the rules specified
earlier are applied

This abdominal CT scan with contrast reveals markedly decreased
attenuation of the liver due to marked steatosis (fatty change). The hepatic
veins with contrast stand out sharply, and the spleen is much brighter. This
patient proved to have non-alcoholic steatohepatitis (NASH), though a
similar appearance of the liver is typical with chronic alcoholism

Severe diffuse
fatty liver
disease.

Diffuse fatty liver. On the pre-contrast HASTE T2-weighted image (a) and the GRE
T1-weighted ―in-phase‖ image (b) the signal intensity of the liver is homogeneously
increased. Conversely, on the GRE T1-weighted ―out-of-phase‖ image (c) the signal
intensity is markedly and characteristically decreased. GRE T1-weighted fat
suppressed sequences (d) are not sufficiently sensitive to small quantities of fat, and
so the liver appears hyperintense as compared with the spleen

IPOP
Geographic fat accumulation
limited to the right lobe of the liver

IPOP
subtraction
Severe
geographic
fatty liver
deposition

Focal Deposition and Focal Sparing
• Slightly less common
• More difficult to diagnosis because
may resemble mass lesions.

1. Fat content
2. Location in areas characteristic of fat
deposition or sparing
3. Absence of a mass effect on vessels and
other liver structures
4. A geographic configuration rather than a
round or oval shape
5. Poorly delineated margins
6. Contrast enhancement that is similar to or
less than that of the normal liver
Imaging findings suggestive of fatty pseudolesions rather than true masses include
the following:

• Segment IV, around falciform
ligament .
• Subcapsular.
• Posterior IV, in front of porta hepatis .
• Anterior I, behind porta .
• GB bed.
COMMONEST LOCATIONS:
FOCAL FAT DEPOSITION
Focal fat deposition adjacent to insulinoma metastases,
probably due to local insulin effects on hepatocyte
triglyceride synthesis and accumulation.

• Adjacent to the falciform ligament
• In the porta hepatis
• In the gallbladder fossa
focal fat sparing
characteristically occurs in specific areas:

Focal fatty sparing. The longitudinal
image demonstrates normal liver (M)
surrounded by liver with increased
echogenicity caused by fatty
infiltration.
Focal fatty infiltration. A longitudinal
image showing hyperechoic area (M)
consistent with focal fatty infiltration.

Focal fatty liver changes
• Focal fatty liver
infiltration.
• Focal fatty sparing

Focal fat accumulation in the liver at US. Transverse image.

Focal Fat Deposition
Focal hepatic steatosis.
Axial US scan of the
liver shows an ovoid,
uniformly hyperechoic
focus (arrow), a finding
consistent with focal fat.

Focal fat accumulation in the liver at CT. Axial contrast-enhanced image obtained during the portal venous phase.

Diffuse fat accumulation with focal sparing at US and CT.

Focal fatty liver deposition.
a CT, axial contrastenhanced
portal phase image in
a 58-year-old woman shows a
hypodense, mildly heterogeneous,
cuneiform lesion in the
posterior aspect of segment IV.
MRI, b axial T1-weighted inphase
and c out-of-phase images
show a signal drop within this
lesion on the opposed-phase
image

Fatty Pseudolesions of the Liver:
Postoperative Changes
Contrast-enhanced CT
scan shows a fatty hepatic
pseudomass due to
omental packing (arrow).
Such a pseudomass is a
common postoperative
finding.

Focal fatty infiltration. A geographic region of decreased
attenuation is demonstrated in the left lobe of the liver. The
hepatic vasculature is seen coursing undisturbed through the
left lobe.

Focal hepatic steatosis. (a) Axial in-phase T1-weighted MR
image shows peripheral high-signal-intensity foci (arrow). (b)
Axial opposed-phase T1-weighted MR image shows a
uniform decrease in the signal intensity of the foci (arrow).

Focal fatty liver. An oval
shaped, well-defined, slightly
hyperintense area
(arrowheads) in the posterior
portion of segment IV can be
detected on the pre-contrast
GRE T1-weighted ―in-phase‖
image (a). The lesion is
heterogeneously hypointense
on the pre-contrast GRE T1-
weighted ―out-of-phase‖ image
(b). In the hepatobiliary phase
after Gd-BOPTA administration
(c, d) the area of focal fatty infiltration appears isointense on the T1-weighted ―in-
phase‖ image (c) and hypointense on the T1-weighted ―out-of-phase‖ image (d).
The decreased uptake of Gd-BOPTA is due to the altered metabolic function in
the area of focal fatty infiltration

Fatty sparing. The liver is fat infiltrated, with a focal area
of sparing seen centrally near the porta hepatic
(arrows). Small vessels course through the spared area,
helping differentiating it from a mass lesion.

Focal sparing on US. B-mode US (a) reveals a hypoechoic area (arrowhead) with a
triangular shape near the surface of the liver.
On color Doppler US (b) an intralesional vessel is clearly visible. Note the absence of
any mass effect. This is typical of focal sparing in fatty liver

Focal sparing. Patient with
Burkitt lymphoma after
chemotherapy. On the US
examination
(a) the liver is extremely
bright
due to hepatic steatosis,
and a round, hypoechoic
nodule (arrowhead) is
visible in segment IV of the
liver.
On the CT study (b-d) the
lesion (arrowhead) does not
show significant
enhancement. This is
indicative of focal sparing in
fatty liver

Focal sparing. Patient with
history of breast cancer and
chemotherapy. US
evaluation (a) reveals an
oval shaped, hypoechoic
area (arrowhead) within a
diffuse fatty liver. This is
considered suspicious for
metastasis. On the MR
examination, this focal area
(arrow) appears
slightly hypointense on the
pre-contrast TSE T2-
weighted image (b),
isointense on the GRE T1-
weighted ―in-phase‖ image
(c), and hyperintense on the
GRE T1-weighted ―out-of-
phase‖ image (d). On the
dynamic images after Gd-
BOPTA administration

(e, f) the lesion does not reveal increased perfusion or wash-out. This is more
indicative of an area of focal sparing in a fatty liver than of a metastasis

IOP imaging demonstrates steatosis with regions of geographic sparing (arrows) in
a patient with NAFLD. Fat-saturated T2 weighted imaging shows diffuse decrease
in signal in the liver in regions with fat accumulation. Regions of geographic sparing
are unaffected by the fat-saturation pulse and therefore have higher relative signal
intensity compared with regions of steatotic liver.

Conventional in-
phase and
opposed-phase
(IOP) imaging is
a well-
established
qualitative
method for
detection and
characterizing fat
within the liver.
Examples of IOP
imaging in
patients with
steatosis
demonstrate a
variety of
patterns
diffuse
diffuse
with mass-
like sparing
geographic
steatosis
lobar

FOCAL FATTY CHANGES
(Atypical Forms)
• Locations.
• Mass effect on vessels.
• CT: Parallel dynamics.
• MI: IPOP

Multifocal Deposition
• Uncommon pattern.
• In this pattern, multiple fat foci are scattered
in atypical locations throughout the liver.
• The foci may be round or oval and closely
mimic true nodules.
• Chemical shift GRE may be helpful, and
• May be seen with regenerative nodules in
cirrhosis
Correct diagnosis is difficult, especially in patients with a known
malignancy.

Other clues indicative of multifocal fat deposition;
• Lack of a mass effect
• Stability in size over time
• Contrast enhancement similar to or less than that
in the surrounding liver parenchyma.
For this purpose, chemical shift GRE imaging is more reliable than CT
or US.

Multifocal Focal fatty liver. Patient
with history of renal cell carcinoma
and chemotherapy. On the CT
examination (a-c), and on the
precontrast
GRE T1-weighted ―in-phase‖ and
GRE T1-weighted ―out-of-phase‖
images (d, e), the heterogeneous,
diffuse fatty infiltration does
not permit the confident definition
of any lesion and in particular a
small and ill-defined area
(arrowhead) in liver segment II. On
the corresponding
HASTE T2-weighted image (f) two
markedly hyperintense lesions
(arrows) can be seen, and the
signal intensity is suggestive of
hemangioma

(c) as hyperechoic skip nodules
(arrowheads), and finally
Multifocal Focal fatty liver
on US. On US
examinations, focal fatty
areas in the liver may
appear with different
patterns:
(a) as hyperechoic
nodules (arrows),
(b) as multiple, confluent
hyperechoic lesions
(arrowheads),
(d) as irregular hyper- (asterisk)
and hypoechoic areas (arrowheads)

Multifocal Focal fatty liver on color Doppler US. On color Doppler evaluation,
a vascular structure (arrowheads) courses, without distortion,
between the hyperechoic nodules that represent focal fatty infiltration

Axial US scan shows patchy, diffuse hepatic Steatosis
(arrow), which simulates an infiltrative tumor.

Multifocal Focal fatty liver on CT. Pre-contrast CT scans show that in moderate forms
of focal fatty liver (a) the ROI values of the liver are lower than those of the spleen.
Conversely, in advanced focal fatty liver (b) the liver is markedly hypodense with ROI
values near 0 HU. Note that in advanced focal fatty liver, vessels are seen as
hyperdense compared with normal liver tissue

(a) that appears slightly hypodense after contrast medium administration (b). In
focal fatty liver with irregular distribution (c, d) numerous small, ill-defined,
hypodense nodules (arrowheads) on the pre-contrast scan (c) demonstrate
heterogeneous enhancement in the portal venous phase after contrast medium
administration (d). Fatty liver with a focal distribution
Multifocal Focal fatty liver
on CT. Fatty liver with lobar
distribution (a, b) is
represented
by a large pseudolesion
(asterisk) on the pre-
contrast CT scan

(e-g) is characterized by a well-defined
hypodense nodule (arrow) on the
pre-contrast examination (e) which does
not show significant enhancement after
contrast medium administration (f, g). Note
the presence of an aberrant vessel within
the pseudolesion (arrowhead)

Multifocal fatty liver. On the US examination (a) multiple ill-
defined, slightly hyperechoic nodules are detected (arrows). The
corresponding pre-contrast CT scan (b) reveals numerous, ill-
defined, slightly hypodense areas (arrows), which do not show
significant enhancement
during the arterial (c) and portal venous (d) phases after contrast
medium injection. Note some vascular structures within the
focal fatty areas (arrowheads in d)

Multifocal Focal fatty liver. On the pre-contrast T2-weighted image (a) the liver
appears homogeneously, slightly hyperintense, whereas on the pre-contrast GRE T1-
weighted ―in-phase‖ image (b) it appears heteogeneous, and ill-defined slightly
hyperintense areas (arrows) can be seen. The corresponding pre-contrast GRE T1-
weighted ―out-of-phase‖ image (c) shows diffuse hypointense areas (arrowheads) in
both liver lobes indicating focal fatty infiltration. During the T1-weighted dynamic study
after contrast agent administration, weak and heterogeneous intralesional
enhancement can be detected in the arterial phase (d). Note that some vascular
structures are clearly visible in the affected areas. In the portal venous phase

(e), areas of focal fatty infiltration (arrows) appear as slightly hypointense
compared to surrounding normal liver tissue. In the hepatobiliary phase after Gd-
BOPTA administration (f) the liver is relatively homogeneous in appearance,
although some of the areas of focal fatty infiltration show slightly decreased signal
intensity. The signal intensity of these areas is relatively
unchanged compared with the unenhanced images; however, these areas appear
slightly hypointense because of the increased signal
intensity of the surrounding normal liver tissue

Multifocal fat accumulation in the liver at CT and MR imaging in a 48-year-old
woman with breast cancer. (a) Unenhanced CT image shows multiple
hypoattenuated 1-cm nodules (arrows). (b, c) T1-weighted GRE MR images
show nodules (arrows) with a signal intensity slightly higher than that of the
normal liver parenchyma on the in-phase image (b) but with a signal intensity
loss on the opposed-phase image (c).

Confluent foci of fat accumulation in the liver at MR imaging.
Axial T1-weighted MR images

• Multinodular hepatic steatosis. (a) Axial in-
phase T1-weighted GRE image shows subtle
hyperintense foci (arrow). (b) Axial out-of-
phase T1-weighted GRE image shows
uniform signal loss in the foci (arrows).

Perivascular fat deposition
and perivascular fatty sparing

Perivascular Deposition
• This pattern is characterized by halos of fat
that surround the hepatic veins, the portal
veins, or both hepatic and portal veins.
• The configuration is tramlike or tubular for
vessels with a course in the imaging plane
and ringlike or round for vessels with a
course perpendicular to the imaging plane.

• An unequivocal signal intensity loss on
opposed-phase images in comparison with
that on in-phase images.
• The lack of a mass effect on the surrounded
vessels are.
Indicative of the diagnosis
The pathogenesis of perivascular fat deposition in the liver is unknown.

Transverse portal venous phase CT images
in 45-year-old man )
show well-defined hypoattenuating TRAME
LIKE halos of fatty infiltration (white arrows)
around hepatic veins in both lobes of liver.
On B, the more caudal scan, in which hepatic veins are
perpendicular to the imaging plane, the halos have a
round or ringlike appearance.
Small hepatic veins inside some halos (black arrows) in
B) are poorly depicted because of location at a lower
level in the cross section..
Attenuation of fatty tissue (37 HU) on these images is distinctly lower than that of spared liver
parenchyma (80 HU) and meets imaging criteria for fatty infiltration of the liver

Periportal fat accumulation
in a patient with a chronic
hepatitis B infection.
Axial unenhanced and
late portal venous phase

The apparent affinity of infiltration for the upper liver segments as opposed to the lower ones on these
images is related to section selection; perivenous fatty infiltration of the liver involved all liver segments.
Halos that surround hepatic veins in the imaging plane (coronal images) are tramlike, and those that
surround veins perpendicular to the imaging plane (transverse images) are ringlike or round. Note also the
evidence of perihepatic ascites on all images
MR images in 58-year-old
woman
OP
IP
IP
OP
Fatty tissue (arrows) surrounding the hepatic veins is subtly
hyperintense on in-phase images and shows unequivocal
signal loss on opposed-phase images, features that confirm
perivascular fatty infiltration of the liver

Transverse (A) and sagittal (B) transabdominal gray-scale US
images of liver in 58-year-old woman with biopsy-proved
alcoholic cirrhosis (same patient as in same image before). US
images, obtained with a sector transducer, show irregular bands
and vaguely nodular areas of hyperechogenicity (arrows). The
perivenous distribution is not appreciable, in part because the
intrahepatic vessels are poorly depicted. Exclusion of underlying
neoplasia is not possible.
MR images in 58-year-old woman

Perivesicular fatty
sparing. hyperechoic
liver with hypoechoic
perivesicular foci.
CT, axial contrast enhanced portal phase image
shows a diffusely hypodense liver (57 HU) in
comparison with the spleen (135 HU) with a
perivesicular spared zone (in segments IV and V).
C axial T1-
weighted in-phase
and d out-of-phase
images show an
important signal
drop of the
liver on the
opposed-phase
image with the
exception of a
perivesicular
spared zone

Perivascular fatty sparing. a Ultrasound image in a 39-year-old man with a clinical
suspicion of non-alcoholic fatty liver disease based on elevated liver enzymes
shows a geographic area of fatty sparing parallel to the right hepatic vein. b
Doppler image shows an absence of mass effect on the right hepatic vein

Subcapsular Deposition
• In patients with renal failure and insulin-
dependent diabetes, insulin may be added to the
peritoneal dialysate during kidney dialysis.
• This route of insulin administration exposes
subcapsular hepatocytes to a higher
concentration of insulin than that to which the
remainder of the liver is exposed.
• Administration of insulin results in a subcapsular
pattern of fat deposition, which may be
manifested as discrete fat nodules or a confluent
peripheral region of fat.

Subcapsular fatty liver deposition. a Axial contrast-enhanced portal phase CT
image in a 58-year-old man with a neuro-endocrine tumour of the pancreas shows
two small hypodense subcapsular hepatic lesions in segment V. MRI, b axial T1-
weighted in-phase and c out-of-phase images show a drop of signal within the two
subcapsular lesions on the opposed-phase image

Differential Diagnosis
• Primary Lesions and
Hypervascular Metastases.
• Hypovascular Metastases and
Lymphoma.
• Perfusion Anormalies.
• Periportal Abnormalities.
The diagnosis of diffuse fat deposition in the liver tends to be
straightforward.

What tumors are pitfalls and can contain microscopic fat?
1. Hepatic adenomas may contain microscopic fat.
2. Hepatocellular carcinomas, angiomyolipoma, and focal nodular hyperplasia
may contain microscopic fat and soft tissue

Primary Lesions and
Hypervascular Metastases
• A mass effect.
• Tend to show vivid or
heterogeneous enhancement.
• May contain areas of necrosis or
hemorrhage
Primary hepatic lesions eg, hepatocellular carcinoma,
hepatic adenoma, and focal nodular hyperplasia.

Primary Lesions and
Hypervascular Metastases
• A mass effect.
• Tend to show vivid or heterogeneous enhancement.
• May contain areas of necrosis or hemorrhage
Infiltrative hepatocellular carcinoma is a notable exception
On CT images, this tumor may exert a minimal mass effect, show
little evidence of necrosis, show the same degree of enhancement
as the normal liver parenchyma, and closely resemble
heterogeneous fat deposition.
Correct diagnosis is usually possible with MR imaging,
but the correlation of imaging findings with serum
biomarkers may be helpful.

Periportal fat accumulation
in a patient with a chronic
hepatitis B infection.
Axial unenhanced and
late portal venous phase
Axial opposed-phase Axial in-phase
Differentiation of adenoma from fatty deposition in the liver in a woman with a long history of oral contraceptive use.
T1-weighted GRE images obtained before and during the hepatic arterial phase
Two round adenoma masses in the left lobe of the liver (arrows in a)
resemble nodular areas of fat sparing.
before (c) and during (d) the hepatic arterial phase show enhancement of
the masses (arrows in c and d) The rounded shape of the lesions, as well
as their location, which is atypical for regions of fatty liver sparing, are
important clues suggestive of tumors

Portal venous phase
Axial unenhanced CT
Differentiation of
hepatocellular
carcinoma from fatty
deposition in the liver.
a nodular liver contour suggestive of cirrhosis, as well
as large gastric varices (arrowheads in b). In b, the right
lobe of the liver appears hypoattenuated in comparison
with the left lobe, a finding that could be misinterpreted
as evidence of regional fatty liver deposition; however,
the mass effect with bulging of the anterolateral border
of the right liver lobe (arrow), the mosaic enhancement
pattern, and the thrombus (t) in the left main portal vein
are strongly suggestive of an infiltrative malignancy.
This is a case of infiltrative hepatocellular carcinoma.

Differentiation of metastases from fatty liver deposition in a woman undergoing
chemotherapy for breast cancer.
show diffuse fatty deposition in the liver and a geographic pseudolesion at
the porta hepatis (arrows in a and b) , a finding that represents focal sparing
Multiple round lesions (arrows in c and d), which are more vividly enhanced than
the liver parenchyma, represent metastases . If unenhanced CT had not been
performed, the region of focal sparing on the contrast-enhanced images may have
been mistaken for an enhanced hypervascular tumor

Hypovascular Metastases
and Lymphoma
• The differentiation of focal or multifocal fat
deposition from hypovascular metastases and
lymphoma in the liver may be difficult.
• The clinical manifestations and imaging
features such as lesion morphology, location,
and microscopic fat content usually permit a
correct diagnosis.
• Chemical shift GRE imaging may be
necessary to assess the amount of
intralesional fat.

Perfusion Anormalies
• Resemble fat deposition but visible
only during the arterial and portal
venous phases.
• Not detectable on unenhanced
images or equilibrium phase
images.

the upper mediastinumThe level of the liver
Differentiation of superior vena cava syndrome from fatty
liver deposition.
a hyperattenuated geographic pseudolesion (white arrow in a) in segment IV, at the anterior
border of the liver, and obstruction of the superior vena cava by a thoracic mass (arrow in b).
With regard to morphologic features, the pseudolesion resembles a focal area of fatty liver
deposition or sparing, but its marked enhancement on early phase images helps confirm that
the lesion represents a perfusion abnormality—in this case, one associated with superior vena
cava syndrome. Note the large systemic collateral veins (arrowheads in a and b) and the
collateral draining vessel in segment IV (black arrow in a).

Differentiation of hepatic venous congestion from fatty liver deposition.
hepatic arterial phase shows irregular areas with low attenuation in the nutmeg pattern,
features that could be mistaken for multifocal or geographic fatty liver deposition.
However, this pattern was visible only on arterial phase images and early portal venous
phase images and not on unenhanced images or images obtained in later phases. A
pericardial effusion also was present. Nutmeg liver is a perfusion abnormality that is
related to hepatic venous congestion from cardiac disease or other causes.

CT images obtained at
the same level in the
liver.
Iatrogenic postbiopsy
arteriovenous
fistula

Periportal Abnormalities
• The US- and CT-based differential diagnosis of
periportal fat deposition is broad and includes
edema, inflammation, hemorrhage, and lymphatic
dilatation.
• Edema, inflammation, and lymphatic dilatation tend
to affect the portal triads symmetrically.
• Hemorrhage characteristically involves the portal
triads asymmetrically and may be associated with
laceration or other signs of injury.
• Thus, if chemical shift imaging is performed, a signal
intensity loss of perivascular tissue on opposed-
phase images permits the correct diagnosis of fat
deposition

Differentiation of periportal inflammation from fatty liver deposition. Axial
contrast-enhanced CT images obtained during the portal venous phase and
the equilibrium phase.
The hypoattenuated halos (arrows) that surround the portal venous tracts in a could be
misinterpreted as perivascular fat accumulation, but they retain contrast material and
appear hyperattenuated in b. Retention of contrast material on delayed images is
suggestive of periportal inflammation with transcapillary leakage of the contrast agent
into inflamed periportal tissue; perivascular fat deposition would not be expected to
retain contrast material. The attenuation of periportal halos should be measured on
unenhanced or delayed phase images, if available, to help differentiate periportal fat
deposition from edema or inflammation.

Pitfalls
• Fat-containing Primary Tumors.
• Low-Attenuation Lesions.
• Focal Sparing that Mimics an
Enhanced Tumor.

Fat-containing Primary Tumors
• Hepatic adenomas, hepatocellular
carcinomas, and, rarely, focal nodular
hyperplasias may have microscopic fat
content.
• Hence, a finding of intralesional fat does not
help exclude these entities, and clinical
findings as well as imaging features such as
morphologic structure, mass effect, and
enhancement characteristics must be
considered.

Differentiation of a fat-containing tumor from fat deposition in the liver.

Differentiation of metastases from
fat deposition in the liver.
•bulging of the liver surface (arrow) and
compression of the right hepatic vein
•multiplicity of lesions
•the mass effect
• predominant round shape,
• the thrombus in the superior mesenteric
vein
• and numerous heterogeneous lymph
nodes
hematogenous metastases from
pancreatic adenocarcinoma.

MR Spectroscopy
a. This technique uses the frequency position along the x-axis to separate and
characterize chemicals within voxels.
b. Localized or single-voxel MRI. Sequences include:
i. Point-resolved spectroscopy (PRESS)
ii. Stimulated echo acquisition mode (STEAM)
iii. A reconfigured STEAM sequence has been reported with breath-hold
acquisition of T2-corrected lipid measurement.
iv. A disadvantage is that a large, single voxel is studied.
c. Spectroscopy shows good correlation to hepatic lipid content, sensitive to as
little as 0.5% lipid change, and potentially useful for therapy assessment,
d. The summation of individual lipid peaks calculates the total liver triglyceride
content.

• Fatty liver is a common imaging finding, with a prevalence of 15%–
95%, depending on the population.
• The diagnostic standard of reference is biopsy with histologic
analysis,
• Fat deposition in the liver may be diagnosed noninvasively with US,
CT, or MR imaging if established criteria are applied.
• The most common imaging pattern is diffuse and relatively
homogeneous fat deposition.
• Less common patterns include focal deposition, diffuse deposition
with focal sparing, multifocal deposition, perivascular deposition,
and subcapsular deposition.
• These patterns may mimic neoplastic, inflammatory, or vascular
conditions, leading to confusion and to unnecessary diagnostic
tests and invasive procedures.
• Assessment of the lesion fat content, location, morphologic
features, contrast enhancement, and mass effect usually permits a
correct diagnosis.
• Chemical shift GRE imaging is more reliable than US or CT for
assessing intralesional fat and may be necessary when findings are
equivocal.
Tips and tricks

Tips and tricks
• USG is sensitive in detecting fatty liver.
• It can not detect liver inflammation and
early fibrosis.
• Liver biopsy is currently gold standard
for nonalcoholic steatohepatitis.
• New noninvasive techniques are
promising.

Transverse CT images at level of liver in 45-year-old woman with abdominal pain and
history of daily alcohol consumption Images obtained before intravenous
administration of contrast material (A) and during the hepatic arterial phase (B), portal
venous phase (C), and equilibrium phase (D) show well-defined hypoattenuating halos
that tightly cloak the hepatic veins in both lobes on images of all phases. Mean
attenuation of hypoattenuating zones on unenhanced images was 28 HU. Infiltration
was subjectively considered most conspicuous on portal venous phase and
equilibrium phase images.
MR images in 45-
year-old woman

halos with hyperintense signal on in-phase images (A, C; obtained with
204/4.76 and flip angle of 30°) and signal loss on opposed-phase images
(B, D; obtained with 204/2.65 and flip angle of 30°), features that confirm
the presence of perivascular fatty infiltration. The pattern of infiltration is
virtually identical to that on the CT images in image before.
MR images in 45-year-old
woman

Transverse CT images at level of liver in 35-year-old man with history of regular alcohol consumption and
clinical diagnosis of human immunodeficiency virus (patient 5). Images obtained before intravenous
administration of contrast material (A) and during the hepatic arterial phase (B), portal venous phase (C), and
equilibrium phase (D) show hypoattenuating (mean attenuation on unenhanced images, –17 HU) halos around
portal tracts (arrows in C), sparing of liver periphery in the right lobe (arrows in D), and ill-defined confluent
zones of perivascular infiltration in the left lobe that mimic a diffuse pattern of fatty infiltration of the liver.
Careful review of all images indicated a predisposition of periportal zones to fatty infiltration. Infiltration was
subjectively considered most conspicuous on hepatic arterial phase and portal venous phase images.

Transverse portal venous phase CT images in 78-year-old woman with no known risk factors for fatty
infiltration of the liver (patient 6). Image obtained at initial CT examination (A) shows two portal tracts
(arrows) surrounded by well-defined hypoattenuating tissue (30 HU). The abnormality persisted but
was less conspicuous on images from follow-up examinations at 52 weeks (B) and 54 weeks (C), as
confirmed by quantitative measurements. CNR for spared liver to fatty infiltration was 7, 5, and 1 at
the first, second, and third (last) CT examinations, respectively. There were slight differences in depth
of inspiration between the serial examinations. The hypoattenuation of central liver segments relative
to peripheral liver segments in B and C may represent mild fatty infiltration in these areas but did not
fulfill the imaging criteria for diagnosis of fatty infiltration of the liver.

NONDIFFUSE FATTY
CHANGE OF THE LIVER:
DISCERNING
PSEUDOTUMOR ON MR
IMAGES ENHANCED WITH
FERUMOXIDES-INITIAL
OBSERVATIONS

• Focal fatty change in a 60-year-old woman. (a) Transverse
nonenhanced CT scan shows a round area (arrows) of low
attenuation on the medial segment of the left lobe of the liver. (b)
Transverse contrast-enhanced CT scan shows normal vasculature
(arrowhead) in the area (arrows) of low attenuation without
displacement, which suggests focal fatty change. (c) Transverse
nonenhanced T1-weighted MR image obtained by using the spin-
echo sequence (480/15) on a 0.5-T imager depicts the lesion as
an area (arrows) of slightly higher intensity. (d) Transverse
contrast-enhanced T1-weighted MR image obtained by using the
spin-echo sequence (480/15) on a 0.5-T imager shows the lesion
is well delineated as an area (arrows) of relatively high intensity.
(e) Transverse opposed-phase MR image obtained by using the
gradient-echo sequence (170/22; flip angle, 30°) on a 0.5-T
imager demonstrates the lesion as a distinct area (arrows) of low
intensity.

• Focal spared area in the fatty liver along the porta
hepatis in a 73-year-old woman. (a) Transverse
nonenhanced CT scan of the liver shows low
attenuation, except for a trabecular area (arrows) of
relatively high attenuation along the porta hepatis. The
finding suggests a focal spared area along the porta
hepatis in the fatty liver. Before contrast enhancement,
the transverse (b) T1-weighted (500/20) and (c) T2-
weighted (2,000/80) spin-echo MR images obtained on
a 0.5-T imager show almost homogeneous intensity in
the liver. After contrast enhancement, the transverse
(d) T1-weighted (500/20) and (e) T2-weighted
(2,000/80) spin-echo MR images obtained on a 0.5-T
imager reveal a focal spared area (arrows) along the
porta hepatis as an area of relatively low intensity.

• Fatty liver in a 57-year-old woman with multiple metastases from colon
cancer. (a) Photomicrograph of the histologic specimen shows
adenocarcinoma and fatty change of the liver; however, there is a thin
spared area between the tumor (T) and the surrounding fatty liver (FL).
(Hematoxylin-eosin stain; original magnification, x40.) (b) Transverse
nonenhanced opposed-phase MR image obtained by using the gradient-
echo sequence (180/3.5; flip angle, 90°) on a 1.0-T imager demonstrates
the spared area around the tumor as a rim (arrows) of relatively high
intensity compared with the surrounding fatty hepatic tissue. Before
contrast enhancement, the spared area is barely discernible on the
transverse images obtained by using the (c) in-phase gradient-echo
(180/7.0; flip angle, 90°) and (d) T2-weighted fast spin-echo
(2,000/99[effective]; echo train length, 11) MR sequences on a 1.0-T
imager. After contrast enhancement, the transverse MR images obtained
by using (e) in-phase gradient-echo (180/7.0; flip angle, 90°) and (f) T2-
weighted fast spin-echo (2,000/99[effective]; echo train length, 11)
sequences on a 1.0-T imager reveal a focal spared area around the
tumor as a rim (arrows) of relatively low intensity.

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