Diagnostic Ultrasound - Abdomen and Pelvis

Hepatic Steatosis
TERMINOLOGY
Synonyms
• Fatty liver, hepatic fatty metamorphosis
Definitions
• Accumulation of increasing amount of triglycerides within
hepatocytes
IMAGING
General Features
• Best diagnostic clue
○ Preservation of normal hepatic architecture
○ Presence of normal vessels coursing through fatty
infiltration
○ Decreased signal intensity of liver on T1W out of phase
gradient-echo images
• Location
○ Focal, multifocal, or diffuse
○ Lobar, segmental, or wedge shaped
– Common along hepatic vessels, ligaments, and
fissures
• Morphology
○ Geographic/wedge shape
○ Multifocal spherical lesions may simulate metastasis or
primary tumor
• Variable imaging features depend on
○ Amount of fat deposited in liver
○ Distribution of fat within liver: Focal vs. diffuse
○ Presence of associated hepatic disease
Ultrasonographic Findings
• Grayscale ultrasound
○ Diffuse fatty infiltration
– Increased echogenicity of liver, becoming more
echogenic than kidney
– Attenuation of US beam by steatosis results in poor
visualization of diaphragm
– Margins of hepatic veins blurred due to increased
refraction and scattering of sound
– Loss of echogenic portal vein walls
– Liver often enlarged and changes shape as volume of
infiltration increases
– US grading of steatosis is subjective and prone to
interobserver variation
○ Focal fatty infiltration
– Hyperechoic nodule/multiple confluent hyperechoic
lesions
– No mass effect, with vessels running undisplaced
through lesion
– Wedge-shaped lobar/segmental distribution
○ Focal fatty sparing
– Hypoechoic area within echogenic liver
– Due to direct drainage of hepatic flow into systemic
circulation
□ Next to gallbladder bed (drained by cystic vein)
□ Segment 4, anterior to portal bifurcation (drained
by aberrant gastric vein)
– No mass effect
CT Findings
• NECT
○ Decreased attenuation of liver compared to spleen
– Normal: Liver 8-10 HU more than spleen (50-65 HU)
– Steatosis: Liver at least 10 HU less than spleen, or
absolute liver attenuation < 40 HU
○ Focal nodular fatty infiltration: Low attenuation
– Common location: Adjacent to falciform ligament
– Due to nutritional ischemia at vascular watershed
• CECT
○ Attenuation measurements and comparisons are less
reliable than NECT
– Dependent on timing relative to contrast
administration
– On venous phase or delayed CECT, steatotic liver is
usually > 35 HU less dense than spleen
○ Normal vessels course through fatty infiltration
○ Dual-energy CT:Steatosis accentuated on lower kVp
sequence
MR Findings
• T1 in-phase GRE (chemical shift): Increased signal intensity
of fatty liver vs. spleen
• T1 out of phase GRE: Decreased or loss of signal intensity of
fatty liver
• T1 C+ out of phase GRE: Paradoxical decreased signal
intensity of liver
• Short T1 inversion recovery (STIR): Fatty areas are low signal
intensity
DIFFERENTIAL DIAGNOSIS
Steatohepatitis
• Diabetic fatty liver, alcoholic hepatitis, nonalcoholic
steatohepatitis (NASH)
• Fatty liver + inflammatory change, fibrosis, and necrosis
• Smooth surface, decreased plasticity
• Hepatic veins show disjointed network-like appearance with
blurred outline
• Increasing fibrosis and scarring
Fatty Cirrhosis
• Dense, firm liver
• Hypertrophied left caudate lobe/atrophy of right lobe
• Heterogeneous, hyperechoic parenchyma
• Rarefaction of hepatic veins
Hemangioma
• Typically well-defined, hyperechoic nodule
• Posterior acoustic enhancement
Metastases or Lymphoma
• Hyperechoic metastases may simulate focal steatosis
• Confluent or infiltrative tumor distorts vessels and bile
ducts
• Diffuse lymphoma infiltration may be indistinguishable
from normal liver or steatosis
PATHOLOGY
General Features
• Etiology
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Diagnoses: Liver
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