Unexpected parasternal musculature during skin-sparing mastectomy and microvascular breast reconstruction.

The sternalis muscle is an uncommon anatomical variant of the anterior thoracic wall. Although regarded as functionally insignificant, its presence may influence diagnostic interpretation, surgical dissection and reconstructive planning in breast surgery. We report bilateral sternalis muscles discovered during bilateral skin-sparing mastectomy and immediate autologous reconstruction in a woman in her late 40s. The sternalis muscles were identified intraoperatively, following which retrospective review of preoperative imaging confirmed their presence. Recognition of this variant aided orientation and safe exposure of the internal mammary vessels during reconstruction. Awareness of the sternalis muscle can prevent imaging misinterpretation, avoid intraoperative confusion and optimise reconstructive outcomes.