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.


• 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.


• 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.

Normal Liver

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.

Fatty Liver

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

Diffuse Deposition

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

Geographic Fat

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

infiltration

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 FAT DEPOSITION

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 FATTY SPARING

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).

Pseudotumoral Steatosis

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

Perivascular Fat

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

Pseudotumoral Fat Sparing

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 mediastinum The 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.

THANK YOU

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.

Full story fatty liver imaging Dr Ahmed Esawy

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