Second-look US: how to find breast lesions with a suspicious MR imaging appearance

Breast magnetic resonance (MR) imaging has high sensitivity in breast cancer diagnosis. The probability of malignancy for additional detected lesions is higher in patients with breast cancer than in the population without malignancy, which is why biopsy or further study should be considered for additional detected lesions. Because of the shortcomings of MR imaging-guided biopsy, second-look ultrasonography (US) may be the preferred next step. Detecting target lesions at second-look US and correlating lesions between the two modalities may be challenging. Using axial MR imaging to localize the lesion with respect to the nipple and the lesion-to-nipple distance can narrow the scan range at US. Evaluating the lesion's location relative to the mammary zones and surrounding tissues, as well as noting its depth, characteristics, and nearby landmarks, will aid in lesion correlation. Doppler imaging, tissue harmonic imaging, and other US techniques can be used to identify subtle lesions. Although malignant breast lesions may appear probably benign at second-look US, decision making for biopsy must be based primarily on MR imaging findings. In sonographically occult, MR imaging-detected lesions with suspicious MR imaging features, the probability of malignancy is much higher than 2%, and MR imaging-guided biopsy must be performed.