Definition:

Lack of lipid or relative lack of lipid within portion of otherwise fatty hepatic parenchyma. 

LI-RADS Categorization:

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

Synonyms:

• Focal sparing, Focal fatty sparing

Characteristic imaging features:

• MRI is more sensitive and specific for detection of hepatic fat sparing than CT.
• At MRI, hepatic fat sparing may be diagnosed if
• The liver 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 (i.e., liver is fatty) AND
• One or more portions of the liver show less signal loss than the rest of the liver on OP compared to IP images or on fat-suppressed compared to non-fat-suppressed images (i.e., portions of liver are less fatty).
• At CT, hepatic fat sparing may be diagnosed if
• The attenuation of the liver measures ≤ 40HU (on unenhanced or enhanced images) or ≥ 10 HU less than that of spleen (on unenhanced images)(i.e., liver is fatty) AND
• One or more portions of the liver are hyperattenuating relative to the rest of the liver (i.e., portions of liver are less fatty).
• Focal hepatic fat sparing usually occurs in similar areas as focal hepatic fat deposition (e.g., adjacent to the porta hepatis, gallbladder fossa, falciform ligament and ligamentum venosum). In diffusely fatty liver, it may occur around the margin of a mass or in an area affected by a perfusion alteration.