Comments:

• Applies only to enhancing observations that, in whole or in part, unequivocally are lower in attenuation or intensity than liver in the portal venous phase.
• Does not apply to non-enhancing observations.
• The degree of arterial phase and delayed phase enhancement is not relevant for characterization of this imaging feature.
• 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).
• Portal venous phase hypo-enhancement is part of the definition of “washout”.
• Washout appearance is a LI-RADS major feature. It is defined as a visually assessed temporal reduction in enhancement relative to liver from an earlier to a later phase, resulting in portal venous phase hypo-enhancement or delayed phase hypoenhancement.