Evaluation of Pectoralis Major Muscle in Patients with Posterior Breast Tumors on Breast MR Images: Early Experience

PURPOSE: To evaluate the ability to use breast magnetic resonance (MR) imaging to assess disease extent in patients with posterior breast masses who are suspected to have tumor invasion into underlying muscle. MATERIALS AND METHODS: Nineteen patients with posterior breast masses underwent three-dimensional, gradient-echo, 1.5-T MR imaging before and after the administration of gadopentetate dimeglumine. Thirteen had deep palpable masses that were clinically determined to be fixed to the underlying chest wall. Twelve had mammographic findings that caused muscle involvement to be suspected, and seven had normal mammograms. All patients underwent surgery. MR images were reviewed and were correlated with histologic findings. RESULTS: Enhancing masses were identified on MR images in all 19 patients. Five (26%) of the 19 patients had masses that abutted the muscles, with obliteration of the fat plane and muscle enhancement. All five had muscle involvement at surgery. In the remaining 14 (74%) patients, no enhancement of muscle was seen; none of these had invasion of the muscle at surgery. CONCLUSION: Extension of adjacent tumor into underlying musculature was indicated by abnormal enhancement within these structures. Violation of the fat plane between tumor and muscle, without other findings, did not indicate tumor involvement of these deep structures.