MR imaging of the breast in patients with positive margins after lumpectomy: influence of the time interval between lumpectomy and MR imaging

OBJECTIVE: Postsurgical contrast enhancement resulting from inflammatory changes at the site of surgery limits the accuracy of MR imaging of the breast in diagnosing residual breast cancer. This study was undertaken to evaluate the influence of the time interval between lumpectomy and MR imaging on the diagnosis of residual breast cancer. MATERIALS AND METHODS: Sixty-eight patients who had undergone excisional biopsy with positive resection margins underwent MR imaging for evaluation of residual breast cancer and possible breast conservation. Patients were retrospectively stratified according to the time interval between lumpectomy and MR imaging. Dynamic and morphologic enhancement features were used for lesion characterization. Imaging findings were correlated with results of histopathology. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for patients waiting 7, 14, 21, 28, 35, and 42 days after initial surgery before undergoing MR imaging of the breast. RESULTS: The time interval between lumpectomy and MR imaging of the breast had the greatest influence on the specificity and negative predictive value of MR imaging, increasing progressively over time. A plateau of highest values of 75% specificity and 86% negative predictive value was reached at 28 and 35 days after surgery, respectively. Although the sensitivity and positive predictive value showed smaller variations over time, peak values of 95% sensitivity and 92% positive predictive value were obtained at 35 and 28 days after surgery, respectively. CONCLUSION: We recommend scheduling patients with positive resection margins no earlier than 28 days after initial surgery for evaluation of residual cancer using MR imaging of the breast.