The surgical anatomy of the ansa pectoralis.

Detailed anatomical knowledge of the pectoral nerves is of clinical importance in surgeries as diverse as limb neurotization, mastectomy, orthopedic procedures and operations related to trauma. The brachial plexus of 200 cadavers were examined in an attempt to clarify the normal origins, courses and variations of the nerves with special emphasis on the ansa pectoralis (AP). In 75% the MPN arose from the anterior division of the inferior trunk of the brachial plexus and in 25% it arose from the medial cord. In 40% of specimens, the LPN arose from a single contributing nerve (anterior division of the superior trunk, 11%; anterior division of the middle trunk 18%; lateral cord, 11%). In the remaining 60% of specimens, the LPN arose from the fusion of two rootlets derived variably from the anterior divisions of the superior and middle trunks and the lateral cord. A single AP was found to be present bilaterally in 200 (100%) of the specimens. Classification of the AP was based upon its origin from the upper or lower rootlet of the LPN, the LPN itself, or from the deep branch of the LPN. AP-1 (42%) arose from the deep branch of the LPN; AP-2 (28%) arose directly from the LPN; AP-3 (25%), arose from the lower rootlets of the LPN and rarely, the AP arose from the upper rootlet of the LPN and crossed posterior to the lower rootlet to communicate with the MPN (AP-4, 5%). Irrespective of the aforementioned types, the AP was found to be present, crossing the second segment of the axillary artery in 90% of the specimens. These results could prove useful during the preoperative planning of neurotization and other surgical procedures involving the axilla.