BREAST, PECTORAL REGION, AND AXILLA LAB (Grant's Dissector (16th Ed.) pp. 28-38) TODAY’S GOALS: 1. Identify the major structural and tissue components of the female breast, including its blood supply. 2. Identify examples of axillary lymph nodes and understand the lymphatic drainage of the breast. 3. Identify the pectoralis major, pectoralis minor, and serratus anterior muscles. Demonstrate their bony attachments, nerve supply, and actions. 4. Identify the walls and associated muscles of the axilla. 5. Identify the axillary sheath, axillary vein, and the 6 major branches of the axillary artery. 6. Identify and trace the cords of the brachial plexus and their branches. DISSECTION NOTES: The donor should be in the supine position. Breast 1. The breast or mammary gland is a modified sweat gland embedded in the superficial fascia overlying the anterior chest wall. Refer to Fig. 2.5A for incisions for reflecting skin of the pectoral region to the mid-arm. Do this bilaterally. Within the superficial fascia in front of the shoulder and along the lateral and lower medial portions of the arm locate the cephalic and basilic veins and preserve these for now. Observe the course of the cephalic vein from the arm into the deltopectoral groove between the deltoid and pectoralis major muscles. 2. For those who have a female donor, mobilize the breast by inserting your fingers behind it within the retromammary space and separate it from the underlying deep fascia of the pectoralis major (see Fig. 2.7). An extension of breast tissue (axillary tail) from the superolateral (upper outer) quadrant often extends around the lateral border of the pectoralis major muscle into the axilla. Make an incision through the nipple and into superficial fascia. Identify one or two of the 15-20 main lactiferous ducts that converge on the nipple. Follow one of these into a glandular lobe of the breast. Between the glandular lobes, observe compartments of fat. Remove some of the fat and locate fibrous strands of tissue that extend from the skin to the deep portion of the breast. These are the suspensory ligaments of the breast and are more pronounced in the superior part of the breast and support the weight of the breast. For those who have a male donor, check with tables that have female donors to identify the components of the breast. 3. For both male and female breasts, probe within the superficial fascia near the midaxillary line to locate and identify lateral cutaneous branches of intercostal nerves within intercostal spaces (Fig. 2.8). Pectoral Muscles 1. Remove the superficial fascia overlying the pectoralis major muscle (Fig. 2.9). Observe the two heads of this muscle: clavicular head (attaches to the medial half of the clavicle) and the sternocostal head (attaches to the lateral border of the sternum and costal cartilages of the upper 6 ribs). The muscle narrows to a tendon that attaches to the lateral lip of the bicipital (or intertubercular) groove. 2. The two heads will be reflected individually. Using a scalpel, detach the clavicular head from the clavicle and reflect the muscle inferiorly. Observe the lateral pectoral nerve and pectoral branch of the thoracoacromial artery entering its deep surface. Identify the cephalic vein within the deltopectoral groove and follow it into the space deep to the clavicular head. It becomes tributary to the axillary vein. Next, mobilize the inferior edge of the sternocostal head by placing your fingers behind the muscle. Proceed to lift and detach this head using a scissors until it is completely free. Reflect the entire muscle laterally. During this maneuver, the pectoralis minor muscle will come into view. 3. Identify the pectoralis minor and trace its attachments from ribs 3-5 superiorly to the coracoid process of the scapula. Observe the medial pectoral nerve passing through this muscle and into the deep surface of the pectoral major. It supplies both muscles. (Q: The lateral pectoral nerve is located medial to the medial pectoral nerve. What is the explanation for this apparent inaccurate anatomic relationship?) 4. Identify the serratus anterior muscle. It attaches anteriorly to the upper 8 or 9 ribs and follows the contour of the ribs posteriorly where it attaches to the anteromedial surface of the scapula. It is innervated by the long thoracic nerve (C5-7), which descends on its external surface. Neurovasculature Nerves. In addition to the motor nerve supply to the pectoral muscles (via lateral and medial pectoral nerves) and serratus anterior (long thoracic nerve), sensory supply to skin of the breast region is provided by branches of the supraclavicular nerves (C3,4) in its superior aspect, and thereafter, by lateral and anterior cutaneous branches of the 3rd to 6th intercostal nerves. Arteries. The medial part of the pectoral region is supplied by branches of the internal thoracic artery which perforate intercostal spaces to supply muscle and breast. The lateral part of the pectoral region is supplied by the pectoral branch(es) of the thoracoacromial artery (Fig. 2.10) and the lateral thoracic artery. Both arteries are branches of the axillary artery. Clean fat and loose connective tissue surrounding the pectoral branch and trace it to the thoracoacromial artery. This artery typically gives rise to 3 other smaller branches (deltoid, acromial, and clavicular, named according to the regions they supply – don’t attempt to locate these). The lateral thoracic artery descends along the lateral border of pectoralis minor muscle to supply it and the serratus anterior. It is the principal blood supply to the breast. The thoracoacromial and lateral thoracic arteries will be identified in the dissection on the axilla. Veins. Unnamed vessels from the pectoral region empty into the internal thoracic and lateral thoracic veins. The internal thoracic vein becomes tributary to the subclavian vein and the lateral thoracic veins drains into the axillary vein. Lymph Nodes Lymphatic drainage of the upper limb and breast pass through groups of lymph nodes located in the axilla. These axillary lymph nodes usually accompany veins and are described in relation to the pectoralis minor muscle. Axillary lymph nodes groups include: • Pectoral (anterior) nodes – nodes associated with the lateral thoracic vein. 75% of lymph from the breast drain into these nodes • Subscapular (posterior) nodes – nodes associated with the subscapular vessels and drain the posterior thoracic wall and scapular region • Humeral (lateral) nodes – nodes associated with the origin of the axillary vein and drain lymph from the upper limb • Central nodes – nodes located deep to the pectoralis minor. These receive lymph from the pectoral, subscapular, and humeral nodes and carry this to the: • Apical nodes – nodes located along the axillary vein medial to the upper medial border of pectoralis minor. Lymph vessels from these nodes unite to form the right and left subclavian lymph trunks. These trunks drain, respectively, into the right lymphatic duct and the thoracic duct. Lymph from the medial quadrants of the breast and pectoral region typically drain into parasternal nodes located inside the chest wall in association with the internal thoracic vessels. DISSECTION NOTES: AXILLA Identify muscles comprising the walls of the axilla. (Dissector p. 35, Fig. 2.11) Anterior wall: pectoralis major, pectoralis minor Medial wall: serratus anterior Posterior wall: latissimus dorsi, teres major, subscapularis Lateral wall: intertubercular (bicipital) groove and tendon of the long head of the biceps brachii Other muscles in the axilla include the short head of the biceps and coracobrachialis (they attach proximally to the coracoid process of the scapula). 1. To view the axilla and its contents, reflect the pectoralis major muscle laterally and the pectoralis minor muscle superiorly and abduct the arm about 45°. 2. Identify the axillary sheath as a loose connective wrapping enclosing the axillary vein, axillary artery, and brachial plexus. Work through the axillary sheath and identify the axillary vein located just anterior to the axillary artery. To facilitate a better view of the artery and its branches, divide the vein proximal and distal to where the cephalic vein enters it and remove the remainder of the axillary vein and its tributaries as you encounter them. Note the presence of lymph nodes associated with the veins. 3. Next, identify the three parts of the axillary artery (in relation to the pectoralis minor). The axillary artery is a continuation of the subclavian artery (name changes at the lateral border of the first rib) and ends at the lower border of teres major (where it becomes the brachial artery). Identify the following branches, keeping in mind the likelihood of variation (nice diagrams in the Dissector, p. 36, Fig. 2.13; p. 37, Fig. 2.14): • First part: first rib to pectoralis minor - 1 branch; superior or supreme thoracic artery • Second part: behind pectoralis minor - 2 branches; thoracoacromial artery/trunk (clavicular, acromial, deltoid, pectoral branches) and lateral thoracic artery • Third part: lateral border of pectoralis minor to teres major - 3 branches; anterior and posterior humeral circumflex and subscapular arteries. Note the subscapular artery has a circumflex scapular branch and then continues as the thoracodorsal artery accompanying the thoracodorsal nerve (middle subscapular nerve). 4. Expose the Brachial Plexus (Dissector p. 37, Fig. 2.14). Review the organization of this plexus (rami, trunks, divisions, cords, and branches). You will likely only see cords and branches in your dissection. The cords are named for their position relative to the axillary artery. Look for the capital "M" anterior to the axillary artery (comprised by the musculocutaneous nerve, median nerve, and ulnar nerve). Identify the following cords and their terminal branches: • Lateral cord. Located lateral to the axillary artery. Identify the musculocutaneous nerve entering the coracobrachialis muscle, and the lateral root of the median nerve • Medial cord. Located medial to the axillary artery.