Implications of Anomalous Pectoralis Muscle in Reconstructive Breast Surgery: The Oblique Pectoralis Anterior

Introduction: Many case reports have described anatomical variants of the pectoralis muscles. However, there is a paucity of published literature on the consequence of such presentations in reconstructive breast surgery. Methods: A 45-year-old female patient with breast cancer presented for left mastectomy and immediate reconstruction with tissue expander. During mastectomy, she was noted to have an extra muscle anterior to her pectoralis major muscle. This variant had not previously been described in the literature and was therefore named the oblique pectoralis anterior. After inspection of the aberrant musculature, the decision was made to release the inferolateral insertion of the accessory muscle with the inferior edge of pectoralis major. An adequate pocket for the expander was created. Results: After routine expansion and implant exchange, muscular coverage of the implant from pectoralis major and the oblique pectoralis anterior muscle approximated 70%. The patient was left with good symmetry and a cosmetic result, despite the challenges presented by her anomalous chest wall musculature. Discussion: Prior knowledge of the various anatomic aberrations described in the literature can prepare a surgeon to properly incorporate and utilize the variant anatomy, should it be encountered, to benefit the outcome of the operation.