Definition:

Enhancement in the arterial phase that unequivocally is greater than that of liver.

If unsure about arterial phase hyperenhancement:

Synonyms:

• Synonyms:Arterial hypervascularity, Hypervascularity in the arterial phase, Increased contrast enhancement in late hepatic arterial phase, Hypervascularity, High attenuation area in the arterial phase, Contrast uptake in the arterial phase
• Preferred term: Arterial phase hyperenhancement
• Rationale for preferred term: 
• Term is applicable to both CT and MR imaging.
• Term is a descriptor of the appearance of the observation rather than a description of the possible underlying physiology, such as vascularity

Comments:

• Applies to observations that, in the arterial phase, unequivocally:
• enhance, in whole or in part, more than liver and
• are higher, in whole or in part, in attenuation or intensity than liver
• Arterial phase hyperenhancement is a LI-RADS major feature used to categorize 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 hyperenhancement may be categorized LR-3, LR-4, or LR-5, depending on diameter and other features. As shown in Table, only masses with arterial phase hyperenhancement can be categorized LR-5.
• At MRI, for observations that are hyper-intense pre-contrast, post-processing with generation of subtraction images may be helpful for characterization of arterial phase hyperenhancement.
• For subtractions to be valid, arterial phase and pre-contrast images need to be co-registered and acquired with the same technique.