Clinical Utility of Real-Time MR-Navigated Ultrasound with Supine Breast MRI for Suspicious Enhancing Lesions Not Identified on Second-Look Ultrasound.

This study evaluated the usefulness of magnetic resonance (MR)-navigated ultrasound (US) for evaluation of magnetic resonance imaging (MRI)-detected lesions not visible on second-look US and analyzed differences in lesion-to-nipple distance between supine and prone positions. Of the 831 consecutive patients who were diagnosed with breast cancer and examined with breast MRI from June 2013 to September 2015, 40 lesions in 37 patients who underwent MR-navigated US for MRI-detected lesions that were not visible on second-look US were included. First, MRI was performed in a prone position using a 1.5-T imager, and second, MRI was performed in a supine position for MR-navigated US. Of 40 lesions, 31 (78%) were identified with MR-navigated US, whereas 5 (13%) lesions disappeared on supine MRI and 4 (10%) exhibited no correlation on MR-navigated US. Of 31 lesions with pathologic confirmation, 7 (23%) were malignant, 2 (6%) were high-risk lesions and 22 (71%) were benign lesions. Comparison of the US findings of benign and malignant lesions revealed that orientation of the lesion differed significantly (p = 0.045), whereas lesion shape, margin and echo pattern did not significantly differ between the two groups (p = 0.088, p = 0.094 and p = 0.412, respectively). Median difference in lesion-to-nipple distance on supine and prone MRI was 8 mm (0-34 mm) in the horizontal direction and 5 mm (0-39.5 mm) in the vertical direction. Thirteen lesions exhibited a >1-cm difference in both horizontal and vertical directions. In conclusion, MR-navigated US was useful for the evaluation of MRI-detected lesions that were not visible on second-look US in breast cancer patients.