Anatomy of the pectoral nerves in plastic surgery
This study has multiple objectives:
- Clarify and provide precise data on the anatomy of the pectoral nerves.
- To provide the necessary data on the anatomy of the pectoral nerves to avoid their iatrogenic sectioning during axillary mastectomy/curage and during axillary breast augmentation.
Origin of the pectoral nerves
The origins and connections of these three branches were relatively variable, particularly in the upper and middle branches. In order to clarify the results of our dissections, we created a classification based on the origins and connections of the upper and middle branches.
In 77% dissections, the upper and middle branches arise separately at the truncal level (Type A).
In subtype A1, the superior branch arises from the anterior division of the superior primary trunk, and the middle branch arises from the anterior division of the middle primary trunk. In one case, the middle branch also received innervation from the anterior division of the lower trunk. These two branches were connected by a loop running from the middle branch to the upper branch. This subtype was present in 62% of dissections.
In the A2 subtype, the superior and middle branches arise from the anterolateral bundle and are not connected. This subtype was present in 15% of cases.
In type B, the upper and middle branches have the same truncal origin. This origin was the lateral bundle in one half of cases, and in the other half the origin was the anterior division of the middle trunk. This type was present in 23% of cases.
The origin of the inferior branch of the pectoral nerves was in all cases the anterior division of the inferior primary trunk.
Path of the pectoral nerves
The upper branch
The superior branch of the pectoral nerves generally arises below the clavicle, laterally to the axillary artery. It then runs directly into the clavicular portion of the pectoralis major muscle, which it usually innervates via three small branches.
The middle branch
The middle branch of the pectoral nerves arises just below the superior branch. It follows the course of the pectoral branch of the thoracoacromial artery into the deep fascia of the pectoralis major muscle, then enters distally into the pectoralis major muscle to innervate its sternocostal portion. The middle branch is generally composed of two branches (80% of cases). We found a pectoral loop running from the middle branch to the lower branch in all our dissections.
The lower branch
The inferior branch appears at the medial end of the axillary artery, close to the lateral thoracic artery. After receiving the pectoral loop, it continues its course deep into the pectoralis minor muscle, distributing one or two branches for its innervation.
Anatomy of the pectoral nerves and their environment in the axillary region
Definition: The hollow of the armpit is located in front of the shoulder blade (scapula), between the chest wall and the upper arm. It is shaped like a truncated pyramid, with four walls, a base and an apex.
Only the anterior and medial walls of the axillary fossa will be described, as these are the ones that concern the pectoral nerves.
Front wall
It is composed of two superimposed muscular planes:
The pectoral nerves run between these two musculoaponeurotic planes.
Pectoralis major muscle (pectoralis major)
The pectoralis major muscle inserts medially on the medial 2/3 of the clavicle, the anterior face of the sternum, the 2nd, 3rd, 4th, 5th and 6th costal cartilages and the fascia of the rectus abdominis and external oblique muscles.
During retropectoral prosthetic implantation, it is this inferior muscle insertion that must be freed to create the prosthetic pocket.
Clavi-pectoro-axillary plane :
The subclavius muscle
The pectoralis minor muscle is stretched from the coracoid towards the 3rd, 4th and 5th ribs.
These two muscles are joined by the clavi-pectoro-axillary fascia.
This fascia inserts at the lower edge of the clavicle, forms the fascia of these two muscles and ends at the deep surface of the axillary fossa to form the axillary suspensory ligament (Gerdy).
The inter-pectoral lodge
The pectoral branch of the thoracoacromial artery, the pectoral nerves and a lymphatic relay (Rotter's interpectoral ganglion) run through this cleavable cellular space between the two musculoaponeurotic planes.
The pectoral nerves
- The superior branch of the pectoral nerves is of little interest in the sub-pectoral approach, as it runs directly into the clavicular portion of the pectoralis major muscle. The risk of injury to this branch during axillary dissection is unlikely.
- The middle branch of the pectoral nerves follows the trajectory of the pectoral branch of the thoracoacromial artery at the deep surface of the fascia of the pectoralis major muscle. There is a risk of injury to the middle branch of the pectoral nerves during dissection of the inter-pectoral compartment.
- The inferior branch appears in the medial part of the axillary artery, close to the lateral thoracic artery. It continues its course in the deep, lateral part of the pectoralis minor muscle. In 65% of dissections, the main branch, which is the widest, pierces the pectoralis minor muscle to reach the pectoralis major muscle, whereas in 35% the main branch passes under the lateral border of the pectoralis minor muscle to reach the pectoralis major muscle. This branch presents a high risk of injury when the breast implants axillary approach or when performing an axillary mastectomy/trimming.
The superficial plane is composed of the serratus anterior muscle, stretching from the spinal edge of the scapula to the first 8 ribs.
The long thoracic nerve (Charles-Bell) and lateral thoracic vessels run along the superficial surface of the serratus major muscle. The nerve of the second intercostal space emerges posterior to the plane of the lateral thoracic artery and anterior to the long thoracic nerve; it crosses the region horizontally, passes above the inferior scapular pedicle and anastomoses with the medial cutaneous nerve of the upper arm (Hirtl's anastomosis) to innervate the base of the armpit and the inner surface of the upper arm. This branch may be injured during an axillary approach, resulting in hypoesthesia or even complete anesthesia of the region.
In all our dissections, the distance between the emergence of the intercostal brachial nerve and the lateral border of the pectoralis major muscle was greater than 1cm.