Definition:

• Relative paucity of iron in a solid mass compared to that of background reference tissue (e.g. iron-overloaded liver).

Usage

• Applies, in iron-overloaded livers, to solid masses that unequivocally have lower fractional iron content than background liver.
• Does not apply to benign entities such as cysts, hemangiomas, confluent fibrosis, and focal scars.
• Lesional iron sparing in a solid mass is an ancillary feature favoring malignancy.
• Radiologists at their discretion may apply lesional iron sparing to upgrade the category of solid masses (up to LR-4).
• At MRI, a mass may be characterized as having lesional iron sparing if:
  • The liver shows signal loss on the second echo of a dual-echo sequence or is more hypo-intense than normal on T2w or T2*w images (i.e. liver is iron overloaded) AND
  • Relative to the liver, the mass shows less signal loss on the second echo of a dual-echo sequence and the  mass is less hypointense on T2w or T2*w images (i.e., the mass has lower fractional iron content than the liver). The difference in signal intensity between the mass and the liver is more pronounced with longer echo times and, if dual-echo imaging is performed, with greater echo spacing.

• At CT, a mass may be characterized as having lesional iron sparing if:
  • The liver has greater attenuation than normal (e.g., hepatic attenuation > 75HU) on unenhanced images (i.e., the liver is iron overloaded) AND
  • Relative to the liver, the mass is less hyperattenuating (i.e., the mass has lower fractional iron content than the liver).

If unsure about feature:

• Do not characterize as lesional iron sparing.

Synonyms:

• Synonyms: Non-siderotic nodule, T1 hyperintense nodule
• Preferred terms: Lesional iron sparing

Background

• HCCs have variable signal intensity on T1w and T2w imaging
• Signal intensity on T1w/T2w imaging may be helpful in differentiating benign nodules from early HCC

Potential pitfalls and challenges

• MRI is more sensitive and specific for detection of lesional iron sparing than CT.
• Signal is not helpful in differentiating benign nodules from early HCC.

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