Breast Procedures

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 (see Figure 6).^[26] 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.

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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.

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.

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Axillary dissection. Shown is a view of the structures of the axilla after completion of axillary dissection.

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.

The incision for axillary dissection should be a transverse or curvilinear one made in the lower third of the hair-bearing skin of the axilla. For cosmetic reasons, it should not extend anteriorly onto the greater pectoral muscle; however, it may be extended posteriorly onto the latissimus dorsi as necessary for exposure. Skin flaps are raised to the level of the axillary vein and to a point below the lowest extension of hair-bearing skin, either as an initial maneuver or after the initial identification of key structures.

The key to axillary dissection is obtaining and maintaining proper orientation with respect to the axillary vein, the thoracodorsal bundle, and the long thoracic nerve. After the incision has been made, the dissection is extended down into the true axillary fat pad through the overlying fascial layer. The fat of the axillary fat pad may be distinguished from subcutaneous fat on the basis of its smoother, lipomalike texture. There may be aberrant muscle slips from the latissimus dorsi or the greater pectoral muscle; in addition, there may be an extremely dense fascial encasement around the axillary fat pad. It is important to divide these layers early in the dissection. The borders of the greater pectoral muscle and the latissimus dorsi are then exposed, which clears the medial and lateral borders of the dissection.

The axillary vein and the thoracodorsal bundle are identified next. As discussed (see above), the initial identification of the axillary vein should be made medially, under the greater pectoral muscle, to prevent injury to low-lying branches of the brachial plexus. Sometimes, the axillary vein takes the form of several small branches rather than a single large vessel. If this is the case, all of the small branches should be preserved.

The thoracodorsal bundle may be identified either distally at its junction with the latissimus dorsi or at its junction with the axillary vein. The junction with the latissimus dorsi is within the axillary fat pad at a point two thirds of the way down the hair-bearing skin of the axilla, or approximately 4 cm below the inferior border of the axillary vein. Occasionally, the thoracodorsal bundle is bifurcated, with separate superior and inferior branches entering the latissimus dorsi; this is particularly likely if the entry point appears very high. If the bundle is bifurcated, both branches should be preserved. The thoracodorsal bundle may be identified at its junction with the latissimus dorsi by spreading within axillary fat parallel to the border of the muscle and looking for the blue of the thoracodorsal vein. The identification is also facilitated by lateral retraction of the latissimus dorsi. The long thoracic nerve lies just medial to the thoracodorsal bundle on the chest wall at this point and at approximately the same anterior-posterior position. It may be identified by spreading tissue just medial to the thoracodorsal bundle and then running the index finger perpendicular to the course of the long thoracic nerve on the chest wall to identify the cordlike nerve as it moves under the finger. Once the nerve is identified, axillary tissue may be swept anteriorly away from the nerve by blunt dissection along the anterior serratus muscle; there are no significant vessels in this area.

The junction of the thoracodorsal bundle with the axillary vein is 1.5 to 2.0 cm medial to the point at which the axillary vein crosses the latissimus dorsi. The thoracodorsal vein enters the posterior surface of the axillary vein, and the nerve and the artery pass posterior to the axillary vein. There are generally one or two scapular veins that branch off the axillary vein medial to the junction with the thoracodorsal vein. These are divided during the dissection and should not beconfused with the thoracodorsal bundle.

The axillary vein and the thoracodorsal bundle having been identified, the greater pectoral muscle is retracted medially at the level of the axillary vein, and the latissimus dorsi is retracted laterally to place tension on the thoracodorsal bundle. Once this exposure is achieved, the axillary fat and the nodes are cleared away superficial and medial to the thoracodorsal bundle to the level of the axillary vein. Superiorly, dissection proceeds medially along the axillary vein to the point where the fat containing level II nodes crosses the axillary vein. To improve exposure, the fascia overlying the level II extension of the axillary fat pad should be incised to release tension and expose the lipomalike level II fat. As noted (see Structures to Be Preserved, above), the medial pectoral nerve passes onto the underside of the greater pectoral muscle in this area and should be preserved. One or more small venous branches may pass inferiorly from the medial pectoral bundle; particular attention should be paid to preserving the nerve when ligating these venous branches.

The next step in the dissection is to reflect the axillary fat pad inferiorly by dividing the medial attachments of the axillary fat pad along the anterior serratus muscle. Care must be taken to preserve the long thoracic nerve. Because there are no significant vessels or structures in the tissue anterior to the long thoracic nerve, this tissue may be divided sharply, with small perforating vessels either tied or cauterized. Finally, the axillary fat is freed from the tail of the breast with the electrocautery or a knife.

There is no need to orient the axillary specimen for the pathologist, because treatment is not affected by the anatomic level of node involvement. A surgical clip is placed at the apex of the dissection to assist the radiation oncologist in planning radiation fields. A closed suction drain is placed through a separate stab wound. (Some practitioners prefer not to place a drain and simply aspirate postoperative seromas as necessary.) The use of fibrin sealants may reduce the incidence of seromas. A long-acting local anesthetic may be instilled into the axilla -- a particularly helpful practice if the dissection was done as an outpatient procedure.

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Cite this: Breast Procedures - Medscape - Apr 01, 2005.