Definition:

Presence of excess lipid within hepatic parenchyma. May be diffuse or focal.

LI-RADS Categorization:

• Observations thought to definitely represent hepatic fat deposition should be categorized LR-1.
• Observations thought to probably represent hepatic fat deposition should be categorized LR-2.
• Observations that are indeterminate for hepatic fat deposition versus intra-lesional fat should be categorized LR-3 or LR-4.

Synonyms:

• Fatty infiltration, Steatosis

Characteristic imaging features:

• MRI is more sensitive and specific for detection of hepatic fat deposition than CT.
• At MRI, hepatic fat deposition may be diagnosed if the liver, in whole or in part, shows signal loss on out-of-phase (OP) compared to in-phase (IP) gradient-echo images or on fat-suppressed compared to non-fat-suppressed images.
• At CT, hepatic fat deposition may be diagnosed if the attenuation of the liver, in whole or in part, measures
• ≤ 40 Hounsfield units (HU) on unenhanced or enhanced images OR
• ≥ 10HU lower than that of spleen on enhanced images.
• On contrast-enhanced images, focal hepatic fat deposition may appear as if an area of darker signal/attenuation was stamped on the liver.
• Hepatic fat deposition may be diffuse, focal, or multi-focal.
• Diffuse hepatic fat deposition affects a large area of the liver (entire liver, lobe, or segment) and may have a homogeneous distribution or a heterogeneous distribution (patchy, perivascular, subcapsular, multi-segmental).
• Focal hepatic fat deposition affects a small area of the liver (subsegmental) and usually has a geographic shape. Less commonly it has a rounded shape. It usually occurs in specific areas (e.g., adjacent to the porta hepatis, gallbladder fossa, falciform ligament and ligamentum venosum).
• If there are multiple areas of focal hepatic fat deposition, the term multi-focal fat deposition applies.