Sentinel Lymph Node Biopsy in Patients With Melanoma Technique

Updated: Oct 14, 2021
  • Author: Amy E Somerset, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
  • Print


After melanoma is diagnosed, if a sentinel lymph node biopsy (SLNB) is deemed appropriate, the patient undergoes wide local excision of the primary melanoma site with SLNB. Some centers routinely wait 24 hours after injection of the radiotracer before performing SLNB. The authors have found, however, performing injection the day of surgery is more practical with similar outcomes.

Lymphoscintigraphy is performed in the nuclear medicine department by injecting the radiotracer intradermally around the primary melanoma, followed by imaging with a gamma camera to confirm appropriate uptake of the radiotracer and provide general localization (see the image below). It may be beneficial to use a handheld gamma probe in the preoperative area to identify potential sites of SLNs. When there are multiple nodal basins, all are considered pertinent. Which basin lights up first does not matter, as all should undergo biopsy.

For optimal SLN mapping in head and neck melanoma, use of single-photon emission computed tomography (SPECT) imaging should be considered. It has been noted to improve anatomic localization of SLNs and to increase the number of SLNs identified, which can result in altered surgical planning, improved extraction of SLNs, and increased identification of regional nodal metastasis with improved survival. [35, 36]

Lymphoscintigraphy of a forehead melanoma with upt Lymphoscintigraphy of a forehead melanoma with uptake in the parotid and submandibular nodes.

After the patient is transported to the operative suite, anesthesia is induced at the discretion of the anesthesiologist in consultation with the surgeon. If dye is to be used as an adjunct to the radiotracer, approximately 1 mL of blue dye is injected intradermally at the site of the lesion. Either isosulfan blue or methylene blue may be used, but methylene blue offers equivalent efficacy at lower cost. The lesion is then massaged for 4-5 minutes to enhance lymphatic drainage.

A handheld gamma probe is used to identify hot spots, which theoretically indicate the location of SLNs. A small incision is then made overlying the hot spot. Clinicians should be aware that  completion lymph node dissection (CLND) (completion lymphadenectomy) may be necessary after pathologic examination and should plan incisions to accommodate this possibility. Clinicians should also have a thorough discussion with the patient regarding the possibility of CLND and how this changes the extent of the surgical procedure.

For nodes in the parotid region, the authors have rarely found it necessary to perform a parotidectomy and facial nerve dissection to complete a SLNB, as the target nodes are generally superficial in the gland. Therefore, a preauricular incision is recommended for hot spots noted in the parotid region. With careful dissection parallel to the facial nerve branches, SLNs can usually be identified without a formal parotidectomy. The authors have found that repeat surgery for CLND can be performed with acceptable risk to the facial nerve, and the literature supports this finding. [37]

After the nodal basin is identified, blue lymphatics can help visually guide the surgeon to the grossly blue nodes (see the first image below). The handheld gamma probe is used to identify hot nodes in the field. Any nodes with significant radiotracer activity are removed and their radioactivity counts are measured ex vivo (see the second image below).

Intraoperative left axillary sentinel lymph node s Intraoperative left axillary sentinel lymph node seen after uptake with blue dye.
Confirmation of the sentinel node based on a high Confirmation of the sentinel node based on a high radioactive count.

SLNs are then sent to pathology for appropriate staining. An SLN is defined as any of the following:

  • Any grossly suspicious lymph node
  • Any node that harbors blue dye
  • Any node whose radioactivity count is greater than or equal to 10% of that of the hottest node removed

In general, dissection is continued until the nodal bed count is less than 10% of that of the hottest node removed. [38] The maximum number of lymph nodes that can be harvested has not been established. The nodes harboring malignancy are likely to be within the first four nodes harvested. Once four negative nodes have been obtained from a single drainage basin, detection of a subsequent positive node within that basin is extremely low. Thus, lymphadenectomy beyond four nodes is unlikely to reveal nodal metastasis and may confer increased morbidity. Once SLNB is complete, wide local excision of the primary melanoma is performed. Particularly when the SLNs are in close proximity to the primary melanoma (common for head and neck melanomas), the surgeon may wish to perform excision of the primary prior to SLNB to reduce gamma emissions from the injection site and facilitate localization of the SLNs.

It is important to stage patients radiographically prior to completion lymphadenectomy. When a SLN is positive, staging studies may obviate the need for CLND in the setting of metastatic disease.


Post Procedure

Pathologic examination

Serial sectioning is important to detect micrometastasis in the pathologic specimen. National Comprehensive Cancer Network (NCCN) Guidelines recommend serial sectioning in addition to appropriate immunohistochemistry. [5] Staining for melanoma markers, including S100, HMB45, and Melan-A/Mart-1, increases sensitivity and can detect one positive cell within 100,000 cells. Consideration can also be given to performing polymerase chain reaction (PCR) on the sentinel lymph nodes (SLNs).

In SLN biopsy (SLNB) for melanoma, unlike that for breast cancer, the utility of routine intraoperative pathologic sectioning is somewhat debatable. Concerns have been raised about the possibility of frozen sectioning disrupting what few malignant cells may be present, preventing further analysis. [39]

In 2000, Koopal et al found that intraoperative frozen sectioning carried a sensitivity of 34% and a false-negative rate of 12%. [40] Tanis et al compared intraoperative frozen sectioning of SLNB for melanoma patients with breast cancer patients and demonstrated sensitivities of 47% and 74%, respectively. [41]

Others have found that frozen sectioning can provide accurate results and minimize trips to the operating room, thereby decreasing potential complications and cost of repeat surgery. [42, 43, 44] In 2008, Alkhatib et al reported a much higher sensitivity rate of 91%, supporting the use of routine intraoperative frozen section. [42]

With regard to head and neck melanoma, intraoperative frozen section should not be performed. Conversion from SLNB to a completion lymph node dissection (CLND) in the axilla or femoral triangle is relatively straightforward. Contrary to this, CLND in the neck may necessitate a lateral neck dissection, posterolateral neck dissection, or formal parotidectomy with facial nerve dissection, procedures that carry substantially more risk to the patient than isolated nodal biopsy. Because of this disparity, it is more practical to await final pathology, allowing a more comprehensive preoperative discussion with the patient. Additionally, in light of the findings of the Multicenter Selective Lymphadenectomy Trial II (MSLT-II), [31] CLND may not be warranted in every patient with SLN metastasis.

Also see Sentinel Lymph Node Biopsy in Melanoma Pathology.



Sentinel lymph node biopsy (SLNB) is associated with fewer complications than a more extensive lymphadenectomy. Radiotracer is generally well tolerated, with mild discomfort at the injection site. There are reports of allergic reactions to blue dye. The procedural false-negative rate is less than 5% for experienced practitioners. Rates of wound infection, nerve injury, deep venous thrombosis, and lymphedema are less than 1%. Hematoma and seroma formation occurs in less than 2% of patients. Risks for complications are greater in the groin compared with the axilla or neck. Specific to head and neck melanoma, facial nerve injury is a feared complication, although rates of injury are very low.

The potential for injury to the facial nerve has led some to recommend a superficial parotidectomy as opposed to mapping the parotid gland. [45] However, a study by Schmalbach et al on 80 patients with head and neck melanoma reported no dysfunction of the cranial nerves, including the facial nerve, and concluded that a superficial parotidectomy is unnecessary for evaluating SLNs in the parotid region. [46] The authors have had similar experiences.

Because the lymphatic system of the head and neck region is complex, some concern exists regarding the possibility of missing metastatic SLNs (ie, false-negative SLNB results) and the potential for recurrence in a nodal bed after a negative SLN dissection. The literature is not unanimous, suggesting a failure rate anywhere from 0-25%. [27, 37, 46, 47, 48, 49] False-negative rates should be below 5%, slightly higher in head and neck region.