Objective: This study was undertaken to determine the frequency and significance of foci of enhancement having no corresponding mammographic or clinical abnormality that are encountered on MR imaging of the breast performed to evaluate mammograms with equivocal findings.
Materials and methods: Reports from MR examinations of 103 patients who underwent MR imaging of the breast to evaluate questionable mammographic findings were retrospectively reviewed. We identified cases that had focal enhancing lesions without a corresponding mammographic or palpable abnormality. Clinical history, mammograms, MR images, and follow-up information were reviewed.
Results: Of the 103 patients, 30 (29%) had incidental foci of enhancement. These women were significantly younger, more often premenopausal, and more likely to have dense breasts than those who did not have incidental foci. Tissue confirmation of the incidental foci was available for seven patients, mammographic follow-up was available for a mean interval of 22 months for 22 patients, and no follow-up was available for one. Cancer at the incidental sites was diagnosed in one of the 30 patients with multiple foci. She was also shown to have cancer at the site originally questioned mammographically (index site). None of the remaining patients has had a diagnosis of malignancy at the incidental sites.
Conclusion: Incidental enhancing foci are common in women undergoing breast MR imaging for questionable findings on mammography, occurring in 29% of our patients. Our results suggest that unless malignancy is diagnosed elsewhere in the breast, these incidental foci are unlikely to be malignant.