Q    Anatomical boundaries of axillary dissection.

    Before the advent of SLN biopsy, axillary dissection was routinely performed in breast cancer patients: it provided
prognostic information that guided subsequent adjuvant therapy, it afforded excellent local control, and it may have
contributed a small overall survival benefit.

Axillary dissection for clinically node-negative breast cancer includes resection of level I and level II lymph nodes and the
fibrofatty tissue within which these nodes lie. The superior border of the dissection is formed by the
axillary vein laterally and the upper extent of level II nodes medially; the lateral border of the dissection is formed by the
latissimus dorsi from the tail of the breast to the crossing point of the axillary vein; the medial border is formed by the
pectoral muscles and the anterior serratus muscle; and the inferior border is formed by the tail of the breast. Level II
nodes are easily removed by retracting the greater and smaller pectoral muscles medially; it is not necessary to divide or
remove the smaller pectoral muscle. In general, level III nodes are not removed unless palpable disease is present.

Figure . Axillary dissection. Shown are axillary lymph node levels in relation to the axillary vein and the muscles of
the axilla (I = low axilla, II = midaxilla, III = apex of axilla).

Axillary dissection, either alone or in conjunction with lumpectomy or mastectomy, usually calls for general anesthesia, but
it may also be performed with thoracic epidural anesthesia supplemented by local anesthesia as needed. To facilitate
identification and preservation of motor nerves that pass through the axilla, the anesthesiologist should refrain from using
neuromuscular blocking agents. In the absence of neuromuscular blockade, any clamping of a motor nerve or too-close
approach to a motor nerve with the electrocautery will be signaled by a visible muscle twitch.

Structures to be Preserved

    There are a number of vascular structures and nerves passing through the axilla that must be preserved during axillary
dissection (see Figure 7). These structures include the axillary vein and artery; the brachial plexus; the long thoracic nerve,
which innervates the anterior serratus muscle; the thoracodorsal nerve, artery, and vein, which supply the latissimus dorsi;
and the medial pectoral nerve, which innervates the lateral portion of the greater pectoral muscle. The axillary artery and the brachial plexus should not be exposed during axillary dissection. If they are, the dissection has been carried too far superiorly, and proper orientation at a more inferior position should be established. In some patients,
there may be sensory branches of the brachial plexus superficial (and, rarely, inferior) to the axillary vein laterally near the
latissimus dorsi; injury to these nerves results in numbness extending to the wrist.

To prevent this complication, the axillary vein should initially be identified medially, under the greater pectoral muscle. Medial to the thoracodorsal nerve and
adherent to the chest wall is the long thoracic nerve of Bell. The medial pectoral nerve runs from superior to the axillary
vein to the undersurface of the greater pectoral muscle, passing through the axillary fat pad and across the level II nodes;
it has an accompanying vein whose blue color may be used to identify the nerve. If a submuscular implant reconstruction
(see Breast Reconstruction after Mastectomy, below) is planned, preservation of the medial pectoral nerve is especially
important to prevent atrophy of the muscle.

The intercostobrachial nerve provides sensation to the posterior portion of the upper arm. Sacrificing this nerve generally
leads to numbness over the triceps region. In many women, the intercostobrachial nerve measures 2 mm in diameter and
takes a fairly cephalad course near the axillary vein; when this is the case, preservation of the nerve will not interfere with
node dissection. Sometimes, however, the nerve is tiny, has multiple branches, and is intermingled with nodal tissue that
should be removed; when this is the case, one should not expend a great deal of time on attempting to preserve the
nerve. If the intercostobrachial nerve is sacrificed, it should be transected with a knife or scissors rather than with the
electrocautery, and the ends should be buried to reduce the likelihood of postoperative causalgia.