Second-Look Ultrasound: When Things Are Not Always as They Seem

The purpose of this study was to compare size, morphologic features, and degree of suspicion between findings at second-look ultrasound (SL-US) and additional lesions with histological confirmation detected on breast magnetic resonance imaging (MRI). We performed an observational retrospective study including women who underwent SL-US between January 2021 and August 2022. Size, morphology according to Breast Imaging Reporting and Data System (BI-RADS) lexicon, and BI-RADS categories were analyzed for MRI and US findings. Two hundred twenty-four consecutive patients (aged 29-88 years; mean, 59.2 years) underwent SL-US to identify 235 additional lesions detected on MRI. US identified 173 (73.6%) findings. US- guided biopsy was performed in 148 (85.5%) of the detected lesions, proving 56 (37.8%) malignant and 92 (62.2%) benign. Mean size was 15.2 mm on MRI and 9.4 mm on US. Foci and masses showed good correlation, whereas nonmass enhancements tended to appear larger on MRI, and this difference was statistically significant (P = 0.0001). Morphology showed a higher agreement in the case of foci and masses than with nonmass enhancements. BI-RADS categories agreed in 66 cases (44.6%), whereas in 61 cases (41.2%), the degree of suspicion was higher for MRI, and in only 21 cases (14.2%) were lesions more suspicious on US than on MRI. In conclusion, lesions detected at SL-US show a higher agreement in size and morphologic features for foci and masses than with nonmass enhancements and similar or lower degree of suspicion than on MRI; therefore, decision to perform a biopsy should be based primarily on MRI findings.