Anatomical study of pectoral nerves and its implications in surgery.

Abstract

This anatomical study of the pectoral nerves and their innervation is to provide detail informations on the pectoral nerves and their variations in their course, to guide the cosmetic and plastic surgeons for their easy intra operative localization and to improve the understanding of the pectoral muscle innervation, which is very much required during breast reconstruction after modified radical mastectomy (MRM) in breast cancer; axillary dissection; removal of the pectoralis minor muscle, and in harvesting the pectoralis major for myocutaneous head and neck island flap surgeries. A total of 50 pectoral region specimens (both right and left sided) from 25 embalmed adult human cadavers (20 female & 05 male) were studied by dissection method. The data were tabulated in Microsoft excel and analysed by using Statistical Package for Social Science (SPSS 17(th) version). Mean, Proportion, Standard deviation and Unpaired t-test were applied for analysing the data obtained. In all the specimens, the medial pectoral nerve pierces the pectoralis minor muscle; but as a single trunk in 76%, and as dividing branches in 34% specimens. The extent of costal attachment of the pectoralis minor muscle found to be less than 6.0 cm in cases of the medial pectoral nerve piercing the pectoralis minor muscle as a single trunk. The medial pectoral nerve after piercing the pectoralis minor, ramify within the muscle supplying it, finally runs along the lateral aspect (lower border) of the pectoralis minor muscle to supply the lower portion or distal segment of the pectoralis major muscle. Similarly, the lateral pectoral nerve runs along the upper border (medial aspect) of the pectoralis minor muscle (98%) and then runs under surface of the pectoralis major muscle along with the pectoral branch of thoracoacromial artery, supplying the upper portion or most of the proximal 2/3(rd) of the pectoralis major muscle. Therefore, when the pectoralis minor muscle is removed in a modified radical mastectomy or during dissection between the two muscles, there is partial denervation of the pectoralis major muscle with partial atrophy and decrease in muscle mass. If the lateral pectoral nerve also injured along with the medial pectoral nerve, it can result in total denervation of the pectoralis major muscle with severe atrophy and fibrosis. In breast augmentation implants placing behind the pectoralis major muscle, it is found to be more advantageous if the pectoralis major muscle is partially denervated for the better projection and contour. The distance of the branches of the medial pectoral nerve and the lateral pectoral nerve in the pectoral muscles from the lateral margin of the sternum being 8.8-10.8 cm and 5.8-10.2 cm respectively. The proximal segment or upper portion of the pectoralis major muscle has got separate independent vascular and nerve supply; therefore, it can be safely used as a myocutaneous flap in surgeries of head and neck or anterior chest wall.