Axilla

Lymphatic drainage: axillary node anatomy

The lymph nodes of the axilla drain the chest, breast and arm; know­ledge of their anatomy is critical for surgeons operating in this area in order to stage disease properly, remove nodes safely and minimize postoperative morbidity.

The axillary nodes are arbitrarily divided into five groups. The lateral nodes lie behind the axillary vein laterally and drain the upper limb. The pectoral nodes lie along the lateral thoracic veins and the lower border of pectoralis minor, and primarily drain the breast. The posterior or subscapular nodes lie along the subscapular vein at the lateral border of the scapula, where they sit anterior to subscapularis and primarily drain the posterior shoulder. The central nodes lie near the base of the axilla and drain the first three groups of nodes; they are the ‘lowest’ nodes in the axilla and the easiest nodes to palpate. The apical nodes lie medial to the axillary vein and the upper border of pectoralis minor behind the clavipectoral fascia ( Fig. 38.4 ). They receive lymph from all the other groups, and drain via two or three subclavian lymph trunks into the confluence of the jugular and subclavian veins. These trunks may or may not first fuse into a common lymphatic duct. The apical nodes lie along the chest wall around the thoracic inlet and below subclavius (Halsted's ligament).

The lateral and central groups of nodes each contain 10–14 nodes. The other groups each consist of 1–7 nodes. A complete axillary node dissection may therefore contain anywhere from 23 to 59 nodes. The node count may actually be higher in some cases, such as patients with low-grade lymphomas in whom normal, tiny, rudimentary nodes not seen in most people become pathologically enlarged.

For the purpose of surgical dissection, the five groups of nodes are usually consolidated into three ‘levels’, based on their relation to pectoralis minor (see Fig. 38.4 ). Level 1 nodes are lateral to the infero­lateral border of pectoralis minor and include the lateral and posterior nodes and some pectoral nodes. Level 2 nodes are posterior to pectoralis minor and include the central nodes and some pectoral nodes. Level 3 nodes are medial to the medial border of pectoralis minor and are mainly apical nodes.

Removal of level 1 nodes (‘one-level node dissection’) can cause arm, shoulder and chest swelling, which can worsen if level 2 nodes are also removed (‘two-level node dissection’). Lymphoedema rates are highest when level 3 nodes are also removed (‘three-level node dissection’ or ‘complete axillary dissection’) because removal of the apical nodes disrupts the jugular–subclavian lymph trunk and greatly obviates any benefit from collateral lymph channel development that may occur after one- or two-level node dissection. Not surprisingly, the almost routine appearance of arm lymphoedema from three-level node dissection can be lowered to 3–10% by limiting nodal dissection to levels 1 and 2. Conversely, the addition of radiation to any level of node dissection increases the risk of lymphoedema fivefold. Axillary web syndrome (lymphatic cording), where a rope-like soft-tissue density develops in the axilla, presenting as a tight band of tissue in the axilla on shoulder abduction, may occur following sentinel lymph node biopsy or axillary lymph node dissection.

Anomalies and variants

Congenital anomalies of the axilla are very common. The axillary vein, which is formed by the union of the paired brachial veins and the basilic vein, may appear to be bifid in the axilla if these structures enter high. Sollazzo et al found an 18% incidence of venous anomalies in the axilla, most commonly a bifid axillary vein in 10% of patients and an angular vein, which is a large branch of the subscapular vein that runs along the chest wall with the long thoracic nerve, in 5% of patients. The axillary artery can also be bifid if it bifurcates in the axilla (seen in 5–10% of patients).

Nerve anomalies mostly involve the intercostobrachial nerves and probably arise during the fifth week of gestation; they are highly variable and very common. The lateral cutaneous branch of the second intercostal nerve pierces serratus anterior, crosses the axilla to the medial side of the arm and joins the medial cutaneous nerve of the arm (medial brachial cutaneous nerve), which supplies sensation to the medial and posterior portions of the upper arm. Although considered to be a single nerve, the intercostobrachial nerve often divides into two or more branches as it crosses the axillary space. The third intercostal nerve frequently gives off a lateral cutaneous branch. As a consequence of splitting of the intercostobrachial nerve, the possibility of another nerve arising from the third intercostal nerve and/or a prominent medial brachial cutaneous nerve, a surgeon dissecting the axilla may therefore expect to encounter anywhere from one to four cutaneous nerves ; the branches of cutaneous nerves crossing the axilla should not be expected to be consistent from one patient to another.

Anomalies of the lymph vessels and muscles of the axilla are also well recognized. Lymphangiomas of the axilla can occur in utero and may be one cause of stillbirth; these benign tumours can grow quite large, can cause bleeding in utero and are usually associated with a normal karyotype. They can now be recognized in utero by ultrasound and treated. The most common muscular anomaly is an axillary arch, a functionally insignificant extension of muscle most often lying between latissimus dorsi and pectoralis major, which occurs in 7–27% of the population and has multiple subvariants, depending on where the muscle is attached. This has implications for axillary dissection: if the arch is mistaken for latissimus dorsi, the operating surgeon may dissect the axilla too laterally, leaving level 1 tissue and possibly injuring the axillary artery or the brachial plexus. Surgeons who carry out axillary dissection need to be able to recognize the presence of an axillary arch and simply divide it.

Axillary dissection

A two-level node dissection is standard for the clearance of macroscopic nodal metastases. Three-level dissection is less indicated today except in those rare instances of gross involvement of the level 3 nodes.

The patient is placed supine with the arm extended on an arm board. The arm should be secured to the board with towels and tape. The author does not generally place a sandbag under the shoulder, to avoid traction on the plexus. Similarly, the author avoids circumferentially prepping the arm, which reduces the risk of pulling up on the arm and stretching the plexus. The arm is prepped free only if there is particularly bulky disease and/or if removal of pectoralis minor is planned. The patient is usually not paralysed, so that nerves may be identified. After wide sterile prepping and draping of the axilla, upper chest and shoulder, the operation is carried out in nine main steps.