Definition:

• Unequivocal decrease in the diameter of an observation, measured on examinations performed on different dates, which is not attributable to artifact, differences in technique between the two examinations, or measurement error.

Synonyms:

• Synonyms: Decreased size

Comments:

• Applies to masses that unequivocally become smaller in absence of treatment (i.e., spontaneously).
• Diameter reduction in the absence of treatment is an ancillary feature that favors benignity. LI-RADS does not stipulate a minimum reduction in diameter required for use as an ancillary feature.
• Radiologists at their discretion may apply diameter reduction to downgrade category.
• Radiologists should exercise judgment in the application of this feature, which applies only to an unequivocal decrease in the diameter of an observation.
• Diameter reduction should be assessed on images in the same plane and, if possible, acquired in the same phase or sequence.
• After treatment, diameter reduction should not be used as an ancillary feature favoring benignity.

Potential pitfalls and challenges:

• For tumors that reduce in size following resorption of acute bleed, diameter reduction should not be used as an ancillary feature favoring benignity.