[Sternalis muscle in breast surgery].

The sternalis muscle is a normal anatomic variant, which exists in about 5 to 8% of people. It runs longitudinally superficial to pectoralis major, alongside the sternum. Although the sternalis seems common in cadaveric studies, physicians are not familiar with it, which may lead to confusion in diagnosis. Occasionally, the sternalis may be misinterpreted as a breast mass on mammogramm. In that case, computed tomography and magnetic resonance imaging are useful. We report herein two cases of sternalis muscles encountered during mastectomy.