Ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) findings of fatty infiltration of the liver.
US: Fatty infiltration is seen as areas of focal or diffuse increased echogenicity that do not demonstrate mass effect on adjacent biliary structures or blood vessels. Fatty infiltration may limit or prevent visualization of intrahepatic vessels, the deeper posterior portion of the liver, and the diaphragm posterior to the liver. Hepatitis or cirrhosis can also present with diffusely increased liver echogenicity.
CT: On NCCT, the liver is normally 8 Hounsfield units (HU) greater in density than the spleen. In fatty infiltration, the spleen is 10 HU more dense than the liver. In diffuse fatty infiltration, the hepatic vessels are more conspicuous and may appear as if they contain contrast even on a NCCT scan. In focal fatty infiltration, the normal hepatic vessels traverse the area of decreased attenuation, a finding not usually present in malignancy. Focal fatty infiltration tends to be in a lobar distribution (wedge shaped) with linear margins. Areas where fatty infiltration or sparing typically occur include the gallbladder fossa, subcapsular, left lobe medial segment near the fissure for the ligamentum teres, anterior to the porta hepatis, and around the IVC.
MRI: Signal differences in focal fatty infiltration of the liver may be subtle. As with CT, vessels should course normally through the area of signal abnormality without mass effect on adjacent structures. MRI with fat suppression is more sensitive than T1-weighted (T1-w) and T2-weighted (T2-w) imaging for fatty infiltration, with fatty infiltration having decreased signal intensity compared with normal liver. Areas of fatty infiltration will also reliably demonstrate decreased signal on opposed-phase T1-w imaging.