Sentinel Lymph Node - Uses

Uses

The concept of the sentinel lymph node is important because of the advent of the sentinel lymph node biopsy technique, also known as a sentinel node procedure. This technique is used in the staging of certain types of cancer to see if they have spread to any lymph nodes, since lymph node metastasis is one of the most important prognostic signs. It can also guide the surgeon to the appropriate therapy.

There are various procedures entailing the sentinel node detection:

• Preoperative planar lymphoscintigraphy
• Preoperative planar lymphoscintigraphy in conjunction with SPECT/CT
• Intraoperative visual blue dye detection
• Intraoperative fluorescence detection (fluorescence image-guided surgery)
• Intraoperative gamma probe/Geiger meter-detection
• Postoperative scintigraphy of main specimen with planar acquisition

In everyday clinical activity, entailing sentinel node detection and sentinel lymph node biopsy, it is not requested to include all different techniques listed above. In skilled hands and in a center with sound routines, one, two or three of listed methods can be considered being sufficient.

To perform a sentinel lymph node biopsy, the physician performs a lymphoscintigraphy, wherein a low-activity radioactive substance is injected near the tumor. The injected substance, filtered sulfur colloid, is tagged with the radionuclide technetium-99m. The injection protocols differ by doctor but the most common is a 500 μCi dose divided among 5 tuberculin syringes with 1/2 inch, 24 gauge needles. The sulphur colloid is slightly acidic and causes minor stinging. A gentle massage of the injection sites spreads the sulphur colloid, relieving the pain and speeding up the lymph uptake. Scintigraphic imaging is usually started within 5 minutes of injection and the node appears from 5 min to 1 hour. This is usually done several hours before the actual biopsy. About 15 minutes before the biopsy the physician injects a blue dye in the same manner. Then, during the biopsy, the physician visually inspects the lymph nodes for staining and uses a gamma probe or a Geiger counter to assess which lymph nodes have taken up the radionuclide. One or several nodes may take up the dye and radioactive tracer, and these nodes are designated the sentinel lymph nodes. The surgeon then removes these lymph nodes and sends them to a pathologist for rapid examination under a microscope to look for the presence of cancer.

A frozen section procedure is commonly employed (which takes less than 20 minutes), so if neoplasia is detected in the lymph node a further lymph node dissection may be performed. With malignant melanoma, many pathologists eschew frozen sections for more accurate "permanent" specimen preparation due to the increased instances of false-negative with melanocytic staining.