Asymmetric mammographic findings based on the fourth edition of BI-RADS: types, evaluation, and management.

Asymmetric breast findings are frequently encountered at screening and diagnostic mammography. However, there has been some confusion about the applicable terminology for describing asymmetric breast findings. The fourth edition of the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) has incorporated changes in the lexicon for asymmetric breast findings to address such problems and improve the clinical utility of reporting. The fourth edition has replaced "asymmetric breast tissue" with "global asymmetry," "density seen in only a single projection" with "asymmetry," and "focal asymmetric density" with "focal asymmetry." Once an asymmetric finding is perceived, it should be determined whether it is due to a definite lesion. To interpret and manage asymmetric breast findings, additional imaging studies such as straight lateral views, rolled views, and spot compression views at mammography and ultrasonography or magnetic resonance imaging should be applied appropriately in a logical work flow, and the radiologist should be aware of the pitfalls and pearls of each technique and modality.