Utility of second-look ultrasound in the management of incidental enhancing lesions detected by breast MR imaging

Purpose. To assess the utility of second-look ultrasound (US) for identifying and characterising incidental enhancing lesions detected by breast magnetic resonance imaging (MRI). Materials and methods. From among 655 consecutive breast MRI studies, 62 lesions (MRI visible, nonpalpable, occult at first-look US and mammography) were recommended for second-look US. MRI enhancement of lesions was mass-like in 59 cases (95%) and non-mass-like in three (5%). Forty-two lesions (68%) were <= 10 mm; only three lesions (5%) were >20 mm. Of all lesions, the Breast Imaging Reporting and Data System (BI-RADS) MRI category was highly suggestive of malignancy in six cases (10%), suspicious abnormality in 33 (53%) and probably benign in 23 (37%). The correlation between MRI lesion appearance, lesion size, histopathology findings and detection rate at second-look US were analysed. The reference standard was histopathology and/or follow-up (range 18-24 months). Statistical analysis was performed with the Fisher exact test. Results. Second-look US identified 44 out of 62 (71%) lesions depicted at MRI. The detection rate at second-look US was higher for mass-like MRI lesions (75%) than non-mass-like lesions (0%), for lesion size >10mm (90%) and for BI-RADS 4 lesions (88%). Second-look US-guided biopsy detected 12 out of 17 (71%) malignant lesions. There was no correlation between the likelihood of carcinoma and the presence of a sonographic correlate. Conclusions. Second-look US is a reliable problem-solving tool in identifying and characterising most incidental MRI findings. It contributes to accurately selecting the cases in which MRI-guided biopsy is required.