Breast MRI after conservation therapy: usual findings in routine follow-up examinations

The objective of our study was to define the usual alterations in the ipsilateral and contralateral breast on MRI of women who have undergone surgery and radiation for the treatment of primary breast cancer.

Database searches identified 744 breast MR examinations of 248 women with newly diagnosed primary breast cancer who had undergone standard breast conservation therapy (BCT) and who had undergone MRI before radiotherapy and at least twice after BCT; these MR examinations were reviewed retrospectively. In each MR study, both breasts were evaluated for background enhancement and cystic alteration. In the treated breast, edema, skin thickening, seroma, and enhancement at the lumpectomy site were assessed.

Background enhancement and cystic alteration decreased bilaterally on MRI after completion of surgery and radiation. Edema, skin thickening, seroma, and enhancement at the lumpectomy site progressively decreased over time. These changes never resolved in some women, with edema present in 25.9% of women at 6 or more years after BCT and seroma present in 3.7%. Lumpectomy site enhancement was seen in 37% of studies obtained in the first 12 months after treatment and persisted in 15% of women at 5 or more years. Rim enhancement was seen in women with seromas, whereas focal enhancement was typically seen in those without seromas. The persistence of lumpectomy site enhancement was seen in 12 of 16 women with fat necrosis, indicated by fat signal in the seroma and was seen in only five of 19 patients without fat seen in the surgery cavity (p = 0.007).

After a patient has undergone BCT, MRI shows changes in both breasts. Although the changes in our study population were greatest in the treated breast, parenchymal enhancement and cystic alteration decrease bilaterally indicating a systemic influence. Edematous changes, seroma, focal enhancement, and skin thickening were seen only in the treated breast. All posttreatment MRI findings decrease progressively, and all may persist. Lumpectomy site enhancement is most persistent in women with fat necrosis.