Position the patient with the arm extended on an arm board with a bump under the shoulder (see Chapter 18). If sentinel node biopsy has been performed at an earlier time, plan an incision that excises and extends the previous scar. It will, in general, be easiest to stay wide of the sentinel lymph node dissection field and dissect in fresh tissue around that field. Excising the old scar may help avoid going back into a scarred area. If sentinel node biopsy was done during the same operative procedure and returned positive, then simply extend the sentinel node incision in both directions. Again, allowing subsequent dissection to progress through fresh undissected planes is generally the safest strategy.

An oblique incision just lateral to the pectoralis major muscle provides excellent access to the axilla, and this lateral location allows the scar to fall behind the muscle, where it is less noticeable. A more cosmetically appealing transverse or U-shaped incision may also be used. A transverse incision should be planned to lie below the hair-bearing portion of the axilla. Patient habitus and location of sentinel lymph node often determine incision preference. As with sentinel node biopsy, in corpulent patients an incision in the line between the axillary fat pat and the breast fat may provide the easiest access to the axilla (see Chapter 20).

After incising the skin, create skin flaps to expose the subcutaneous tissues.

Discrete superficial and deep fascia is not encountered in the axilla. Instead, the axillary fascia (derived from the fascia of the pectoralis major, latissimus dorsi, serratus anterior muscles, and investing the muscles of the arm) is adherent to the superficial fascia and is, in the hollow of the armpit, along with the suspensory ligament of the axilla, a continuation of the clavipectoral fascia.

The axillary lymph nodes are predominantly located on the medial side of the axillary neurovascular bundle, and along the medial axillary wall. Terminology is complicated by multiple nomenclature systems including the anatomic system, Haagensen’s system (explained later in this chapter), and the surgeon’s topographic levels I to III (as shown in Fig. 21.1). The anatomic lateral group on the third part of the axillary neurovascular bundle drains the upper limb. The subscapular group located around the subscapular artery and vein drains the shoulder and posterior thorax. The pectoral group associated with the lateral thoracic vessels along the inferolateral border of the pectoralis major muscle drains the anterior thoracic wall including the lateral breast. These three groups drain into the central group lymph nodes located on the second part of the axillary neurovascular bundle which then further joins with the upper outer quadrant of the breast to drain into the apical group.

Surgeons commonly use a different terminology (topographic) for axillary lymph nodes. Topographic group I nodes include the pectoral, subscapular, and lateral nodes. These are the nodes lateral to the pectoralis minor muscle. Topographic group II nodes are under the pectoralis minor muscle and correspond to the central nodes, whereas topographic group III nodes are medial to the pectoralis minor muscle and correspond to the apical nodes (see Fig. 21.1).