A supernumerary muscle complicated axillary lymphadenectomy: case report

During lymphadenectomy in the left axilla of a 38-year-old woman with a 1.4 cm invasive ductal breast carcinoma, when the surgeon attempted to prepare the lateral margin of the pectoralis major muscle, an aberrant muscular slip was observed slightly lateral and deep to the pectoralis major muscle. The two muscles were separated by a narrow band of connective tissue that was completely dissected. Following this, the supernumerary muscle located in the center of the surgical field was pulled towards the latissimus dorsi muscle. As a result, the muscle formed an arcuate course and the lymphadenectomy was carried out troublesomely through a limited field. Nevertheless, the amount of the lymph node dissected was satisfactory (N: 0/25). Based on the anatomical characteristics of the muscle, it was recognized as a pectoralis quartus muscle. To our knowledge this is the first report of a pectoralis quartus muscle as a surgical finding. The surgeon should be aware of the possible presence of this supernumerary muscle as well as its anatomical characteristics in order to avoid any complications.