Subcategorization of Ultrasonographic BI-RADS Category 4: Assessment of Diagnostic Accuracy in Diagnosing Breast Lesions and Influence of Clinical Factors on Positive Predictive Value.

To evaluate the diagnostic accuracy of subcategories 4a-4c of the second edition of the Breast Imaging Reporting and Data System (BI-RADS) ultrasonography (US) lexicon, and to investigate whether clinical factors influence the positive predictive values (PPVs). Overall, 1240 breast lesions in 1227 women diagnosed on ultrasound as category 4 and with pathology were included. The PPV with 95% confidence interval (CI) was 13.6% (95% CI: 11%, 16%) in BI-RADS 4a, 50.0% (95% CI: 44%, 56%) in BI-RADS 4b and 86.0% (95% CI: 82%, 90%) in BI-RADS 4c. Patients' age significantly affected PPVs for subcategories 4a-4c, whereas radiologists' experience and application time had little influence on PPVs for subcategories 4a-4c. In conclusion, the diagnostic accuracies of subcategories 4b and 4c were superior to subcategory 4a. Patients' age significantly affected PPVs for subcategories 4a-4c. Utilizing the subcategories of category 4 was a feasible method regardless of radiologists' experience and application time.