Definition:

Enhancement in the delayed phase that unequivocally is less than that liver.

Comments:

• Applies only to enhancing observations that, in whole or in part, unequivocally are lower in attenuation or intensity than liver in the delayed phase.
• Does not apply to non-enhancing observations.
• The attenuation or intensity of the observation should be compared to that of the adjacent liver parenchyma. If the liver parenchyma visually consists of both nodules and fibrosis, then attenuation or intensity of the observation should be compared to that of the composite liver tissue (i.e., a visual average of the nodules and fibrosis) (see schematics).
• The degree of arterial phase and portal venous phase enhancement is not relevant for characterization of this imaging feature.
• Delayed phase hypoenhancement is part of the definition of washout appearance.
• Washout appearance is a LI-RADS major feature. It is defined as a temporal reduction in enhancement relative to liver from an earlier to a later phase, resulting in portal venous phase hypoenhancement or delayed phase hypoenhancement.