Anatomy of the pectoral nerves and their preservation in modified mastectomy

Abstract

The upper part of the pectoralis major muscle is innervated by the medial pectoral nerve, whereas the lateral pectoral nerve supplies approximately the lower third of the muscle. The lateral pectoral nerve is closely associated with the pectoralis minor muscle, with its branches passing through or around the lateral margin of the muscle, or both. As a result, the nerve may be compromised during division, retraction or removal of the pectoralis minor muscle and during resection of the central and anterior lymph nodes. The medial pectoral nerve distributes with the thoracoacromial vessel branches, and both should be avoided during removal of the lymph nodes at the apex of the axillary space. Injury to the lateral pectoral nerve by accidental division or by evulsion produces variable postoperative atrophy, fibrosis and shortening of the lower third of the pectoralis major muscle, with limitation of shoulder motion and change in the cosmetic contour of the pectoral region of the chest. Routine removal of the pectoralis minor muscle and the lateral pectoral nerve as described by Patey and Handley during their modified mastectomy is not recommended because of the loss of innervation of the lower part of the pectoralis major muscle. The medial and lateral pectoral nerves described herein were named according to their anatomic position in the pectoral area. Furthermore, it is suggested that the use of the terms medial and lateral as applied to these pectoral nerves should denote their actual course, location and distribution and not perpetuate the confusing traditional practice of reversing the names of these nerves on the basis of their origin.