"Category 4A" microcalcifications: how should this subcategory be applied to microcalcifications seen on mammography?

Background The BI-RADS provides descriptors for microcalcifications based on morphology and distribution. However, the descriptor for category 4A microcalcifications is not specified in the 5th BI-RADS nor in the prior editions. Purpose To investigate how the category 4A assessment is applied to suspicious microcalcifications, and the appropriate descriptors for category 4A assessment for microcalcifications seen on mammography. Material and Methods From June 2008 to November 2011, 296 women with 305 suspicious microcalcifications that were assessed as BI-RADS category 4A, who underwent imaging-guided biopsy or surgery, were included. Mammograms were reviewed and imaging features were analyzed according to the morphology and distribution descriptors of the 5th edition of BI-RADS. Pathological results were considered as the reference standard. Positive predictive values were calculated and compared between morphology and distribution descriptors. Results The overall positive predictive value (PPV) of category 4A microcalcifications was 17.7% (54/305). Most common descriptors for category 4A microcalcifications were amorphous morphology (73.1%) and grouped distribution (71.1%). PPVs of individual morphology descriptors were as follows: amorphous = 7.2%; coarse heterogeneous = 12.8%; fine pleomorphic or fine linear/fine linear branching = 91.4% ( P < 0.001). PPVs of distribution descriptors were as follows: regional = 13.2%; grouped = 16.1%; linear/segmental = 54.5% ( P < 0.001). For morphology and distribution descriptors combinations, PPVs for amorphous/regional and amorphous/grouped microcalcifications were 6.8% and 6.9%, while PPVs of other combinations were higher than 10%, respectively. Conclusion Common descriptors used in category 4A assessment for microcalcifications are amorphous morphology and grouped distribution. PPV of amorphous/regional and amorphous/grouped microcalcifications were suitable for category 4A assessment.