Sentinel lymph node dissection is an important procedure in the staging of patients with cutaneous melanoma. Sentinel lymph node dissection is indicated in patients with clinically node-negative melanoma of intermediate or greater thickness (>1 mm). It is considered for melanomas between 0.8 and 1 mm in depth. If thinner, the melanoma should have associated high risk factors such as ulceration or a mitotic count per square millimeter of 1 or more. Additional risk factors to be considered are age, site, Clark’s level of invasion, and gender. Skin melanomas have a straightforward lymphatic flow that can be mapped. Sentinel lymph node dissection should be considered prior to a wide excision of the primary melanoma site, however. This is especially important if a rotational skin flap is planned for closure because the resulting scar will alter the dermal lymphatic flow. A sentinel lymph node dissection that uses both radionuclide and blue dye is highly accurate in finding positive lymph nodes. It allows a focused pathologic examination by the pathologist with both routine hematoxylin and eosin and immunohistochemical staining on the lymph nodes that are most likely to contain metastases.
In the melanoma example shown in FIGURE 1, the cutaneous lesion was excised from the midportion of the patient’s back. This is considered a watershed area—that is to say, the lymphatic drainage may go to either axilla or groin. Accordingly, a preoperative lymphoscintigram is required to demonstrate which lymphatic basin receives the lymphatic drainage from the tumor site. The most common areas are the axillary and inguinal regions for extremity or truncal lesions and cervical or supraclavicular regions for head and neck primaries. Other sites include deep iliac, hypogastric, and obturator regions and the popliteal or epitrochlear regions for legs and arms, respectively. Finally, ectopic sites are also possible.
The skin must be cleared of any active infections, as must the excision site for the melanoma. Preparation, inspection, and monitoring of the radionuclide solution must be coordinated with the nuclear medicine staff.
A few hours before operation, the patient is injected with a radionuclide solution intradermally about the perimeter of the surgical site using sterile technique. This may be done by the radiologist or the surgeon. The commercially available human serum albumin or sulfur colloid solution tagged with technetium-99m is filtered and sterilized. For melanoma, four syringes of approximately 100 μC of technetium-99m filtered sulfur colloid and 0.1 mL of normal saline each are prepared, for a total dose of about 400 μC. The area for injection is prepared with an antiseptic solution. Disposable paper drapes are widely placed, and the physician is gloved. Extensive shielding for radioactivity is not required, but the site and supplies are monitored with a radiation survey meter. A time-out is performed. The gloved physician injects the radionuclide in an intradermal pattern about the incision (FIGURE 2). The area is ...