ACR LI-RADS

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Definition:

Enhancement in the arterial phase that is equivalent to that of liver.

If unsure whether arterial phase enhancement is hyperenhancement vs. isoenhancement:

Comments:

Applies to enhancing observations that in the arterial phase do not in any part unequivocally enhance more than liver.
Does not apply to non-enhancing observations.
Arterial phase hypo- or isoenhancement is a LI-RADS major feature for categorization of masses that are neither definite benign entities nor probable benign entities and that lack features of non-HCC malignancy or tumor in vein. For such masses, those with arterial phase hypo- or isoenhancement may be categorized LR-3 or LR-4, depending on diameter and other features. As shown in Table, masses without arterial phase hyperenhancement cannot be categorized LR-5.

Rationale: Masses with arterial phase hypo- or isoenhancement cannot be diagnosed with 100% certainty as HCC based on imaging alone, regardless of other features. While such masses may represent HCC, the differential diagnosis includes non-malignant entities as well as non-HCC malignancy.

At MRI, for observations that are hyperintense pre-contrast, post-processing with generation of subtraction images may be helpful for characterization of arterial phase hypo- or isoenhancement.

For subtractions to be valid, arterial phase and pre-contrast images need to be co-registered and acquired with the same technique.

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