Anthony Visioni and Julian A. Kim

Introduction

Several cancers, including breast cancer and melanoma, are similar in that regional lymph node metastasis greatly impacts treatment, chance of recurrence, and survival rate. Therefore, management of regional lymph node metastasis is of great interest in patients with these diseases. Previously, the standard of care for a patient diagnosed with invasive cancer was to perform a lymphadenectomy—removal of all regional lymph tissue. Although associated with high morbidity, the procedure was performed to diagnose and treat regional lymph node disease and to correctly stage a patient for further systemic therapy.

Sentinel lymph node biopsy (SLNB) has dramatically changed the management of breast cancer and melanoma patients. The procedure was first described in 1977 by Cabanas for penile cancer; diagnostic and therapeutic applications have since grown. Instead of routine lymphadenectomy, patients who are clinically node negative can now be accurately staged with minimal morbidity.

Dye/Radiotracer and Injection Sites

The injection site for the blue dye or the radiotracer can be either over the tumor or the areola (Fig. 48-1). In the operating room the surgeon then looks for a blue lymph node (if dye is used), a radioactive lymph node (if radiotracer is used), or both. With a radiotracer, multiple nodes may be radioactive. It is important to search for the node with the highest level of radioactivity. This node, as well as all nodes with more than 10% of the highest count, should be removed for pathologic evaluation.

In breast cancer, the choice of blue dye or radiolabeled colloid to perform SLNB has been the subject of multiple studies. Some studies report that the combination of blue dye and radiolabeled colloid is optimal for identification of sentinel nodes, whereas other studies show equivalence. In general, the choice of blue dye or radiolabeled colloid should be dictated by surgeon preference as well as contraindications in patients (e.g., pregnancy, allergy).

Lymphatic Drainage

Another important consideration is the choice of injection site. The lymphatic drainage of the breast and overlying skin are the same: both drain to the axillary lymph nodes. Therefore, intradermal injection (vs. peritumoral injection) of radiotracer is an acceptable practice. Periareolar and subareolar injections work equally well for SLNB. However, intradermal injection of blue dye may lead to skin discoloration and should be avoided in breast cancer. This approach contrasts with melanoma, in which intradermal injections are required; the discoloration of the skin is irrelevant because a wide local excision will be performed at the time of SLNB (Fig. 48-1).

In the case of melanoma, injection of radiolabeled colloid allows for preoperative lymphoscintigraphy. The lymphatic drainage is more variable in melanoma; therefore, lymphoscintigraphy with use of intraoperative gamma probe increases the likelihood of identifying the sentinel lymph node in melanoma involving various anatomic locations.

Lesion Drainage to Lymph Nodes

Unlike breast cancer, the variable locations of cutaneous melanoma lead to SNLB being performed in multiple locations. Typically, upper-extremity melanoma will drain to the axillary lymph nodes, although epitrochlear lymph nodes may also contain the sentinel node in distal tumors (Fig. 48-2, A). Lesions of the scalp typically drain to the posterior cervical lymph nodes, whereas lesions of the face and oral cavity usually drain to the anterior cervical lymph nodes (Fig. 48-2, B). Lower-extremity tumors can drain into the popliteal or inguinal node basins (Fig. 48-2, C and D).

Incisions for the sentinel lymph node biopsies are guided by the expected location of sentinel nodes. For breast cancer, a curvilinear incision at the inferior margin of the axillary hairline is almost uniformly used. This approach allows excellent access to the axilla, as well as excision of the scar if subsequent lymphadenectomy is required. This incision is also used for melanoma in the axilla. Preoperative lymphoscintigraphy for patients with melanoma will indicate if there is an epitrochlear or popliteal sentinel node in tumors of the distal extremity. If a node is found in these beds, a small axial incision over the bed will suffice. If the sentinel node is located in the inguinal region, a 3-cm axial incision below the inguinal ligament should provide the necessary exposure. However, these incisions can be tailored to the location of the sentinel nodes seen on lymphoscintigraphy.

Identification of the Sentinel Lymph Node

After entering the approximate area of the sentinel node, the surgeon begins localized dissection. If blue dye is used, careful dissection is performed until a blue node is discovered. If radiolabeled colloid is used, a gamma probe will guide the dissection (Fig. 48-3, A).

It is important to understand the relationship between the injection site and the direction the probe is pointing. In a phenomenon referred to as “shine through,” pointing the gamma probe in the direction of the injection site could cause falsely elevated counts and mislead the approach of the dissection. It is also important to understand this principle, as it applies to the lymph nodes themselves.

After identifying a “hot” lymph node (Fig. 48-3, B), the surgeon should examine the tissue directly behind it to ensure that the node is truly hot and not just registering background from another node (Fig. 48-3, C).

Summary

Both radiolabeled colloid and blue dye can be used with equivalent identification of sentinel nodes. In breast cancer, subdermal, intradermal, periareolar, and subareolar injections lead to equivalent identification of sentinel nodes, although prior axillary surgery, multicentric tumors, and other factors may affect the choice. Intradermal blue dye should be avoided in breast cancer. Sentinel lymph node biopsy usually does not require extensive deep dissection, but care is taken in the axillary, inguinal, and popliteal dissection to avoid vascular structures. When using radioactive colloid, the surgeon should remove the node with any highest count and any nodes within 10% of the highest count should be removed.

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