Recalibrating the decision for MRI-directed breast ultrasound in patients with newly diagnosed breast cancer, factors predicting sonographic success

Objective: Evaluate utilization of MRI-directed breast ultrasound (US) in patients with newly diagnosed breast cancer and refine practices to increase success of sonographic lesion detection. Methods: This retrospective single-institution review was restricted to women with breast cancer who underwent MRI from November 2006 to January 2017. Enhancing breast lesions, separate from the index tumor, recommended for MRI-directed US were assessed to see which were detected and which characteristics predicted success in detection. Univariate mixed-effects logistic modeling predicted likelihood of finding breast lesions with US, with odds ratios reported. All tests were two-sided with p < 0.05 considered significant. Results: A total of 275 patients underwent MRI-directed US for 361 breast lesions, of which 187 (51.8%) were found on US. Of those detected, 171 (91.4%) were masses and 16 (8.6%) were nonmass enhancement (NME), with masses 14 times more likely to be seen (p < 0.001). Size alone was not a significant predictor but achieved significance when associated with lesion type (mass size, p < 0.001). Masses with irregular shapes or margins and invasive carcinomas were more frequently detected. Patient age, internal enhancement pattern, and distribution of NME were not significant predictors in sonographic detection. A presumed sonographic correlate for NME was found for 16 (16.2%) of 99 attempted lesions. Conclusion: As MRI access expands, utilization of MRI-directed US should be scrutinized to avoid downstream practice inefficiencies. Sonographic detection rates for NME remain low for women undergoing MRI for disease extent, with NME often better suited for MRI-guided biopsy.