Sentinel Lymph Node Biopsy for Squamous Cell Carcinoma Technique

Updated: Dec 07, 2017
  • Author: Mark J Jameson, MD, PhD, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
  • Print
Technique

Approach Considerations

Anatomic planning

Anatomic planning should follow similar principles to standard neck dissections. See Neck Dissection Classification.

Next:

Overview of Sentinel Lymph Node Biopsy

At operation, 1-2 mL of Patent Blue V dye can be used, although this has decreased in popularity. To approximate the same injection sites as for radiocolloid, ensure that the same person performs all the injections. A suitable incision is made in the neck in such a position as to facilitate excision of the incision scar if a subsequent neck dissection is necessary.

The handheld gamma probe is used to identify radioactive sentinel nodes, including those marked preoperatively during lymphoscintigraphy. To reduce detection of radiation from the injection site, a series of malleable, sterilized lead plates may be used to mask the injection site, thus aiding in vivo identification of radioactive nodes. Radioactive nodes are excised, and radioactivity within the node is confirmed ex vivo.

If the blue dye is used, stained lymphatics, if seen, are followed to the first draining lymph node, which is then harvested. Sentinel nodes are labeled according to their color and radioactivity. The anatomic neck level of the sentinel nodes is noted. Although sentinel nodes are usually harvested prior to treatment of the primary tumor, the proximity of the sentinel node to the injection site may require a further search for sentinel nodes following excision of the primary tumor. If sentinel nodes are sought after excision of the injection site, the nodes are not likely to be stained blue.

Because of the relatively high radioactivity present in the injection sites and the proximity to the sentinel node, detection of scattered radiation must be avoided as far as possible. This is particularly true in the floor of mouth. In addition to the use of the lead plates described above, the gamma probe must have a well-collimated detector, which excludes gamma radiation except over a small angle in front of it. Set the pulse-height analysis window to only include the technetium-99m photopeak with a cutoff on the low-energy side at approximately 130 keV. Check the calibration at regular intervals of not more than 1 month (depending on the make and model of the instrument). Devise a quick check of calibration, and perform this quick check before each use. Calling on appropriate scientific or technical assistance may be necessary to ensure the gamma probe is at its optimal settings and to make an estimate of its sensitivity at these settings.

Sentinel nodes are fixed in 10% neutral, buffered formalin, and, after fixation, they are bisected through the hilum (if identifiable) or through the long axis of the node. If the halves are thicker than 2 mm, the slices are further trimmed to provide additional blocks of 2 mm. If sentinel nodes are found to be free from tumor after the initial histologic examination, step-serial sections are prepared at an additional 6 levels in the block at intervals of approximately 150 µm. One hematoxylin and eosin (H&E)–stained section is prepared at each level. If the nodes still appear negative after histologic examination, an adjacent section from each level is examined by immunocytochemistry using the multicytokeratin antibody AE1/AE3.

Previous
Next:

Pathology Code Description

Step-sectioning sentinel lymph nodes

The current histopathologic routine is to step-section the sentinel lymph nodes (SLNs) at multiple levels and to perform immunohistochemical staining as appropriate to identify micrometastatic disease. If any question remains about abnormal cells after the first sections are taken, additional sections are obtained. Immunohistochemistry results identify an additional 10-20% of patients with positive SLNs, in whom micrometastases are not seen on routine sections stained with permanent H&E. At least some of the increased rate of detection of micrometastatic disease is attributable to step-sectioning at multiple levels.

The approach for sampling involves bivalving the lymph node, fixing the two halves face down, and subsequently sectioning each half into 10 sections, which are alternately used for H&E staining, immunohistochemistry testing, and molecular staging. The sensitivity of intraoperative frozen section examination of the SLN is disappointingly low (<50%), although false-positive results are almost never reported. Because of concerns about tissue loss during the frozen section procedure, most centers eschew frozen sections and rely on permanent sections, except to confirm grossly suggestive metastatic disease.

Multiple histopathologic staging systems have been proposed.

In one, the interpretation of the histopathology and immunocytochemistry results for the SLN is categorized as stages 1 through 5, as follows:

  • Stage 1 tumor: In stage 1, the sample is positive for tumor upon first examination using H&E stain.
  • Stage 2 tumor: In stage 2, the sample initially appears negative for tumor, but it is noted to be positive for tumor upon examination of the H&E stain of step-serial sections.
  • Stage 3 tumor: In stage 3, the sample is negative for tumor at stages 1 and 2 but positive for tumor based on immunohistochemistry results. To be categorized as positive for tumor, cells must be present that are positive based on immunocytochemistry results and are cytologically observed to be nucleated cells with the characteristics of viable epithelial cells in both the immunocytochemical preparation and the serial H&E-stained sections. Cytokeratin positivity lacking the cytological features of viable tumor cells is categorized as stage 4.
  • Stage 4 tumor: In stage 4, cytokeratin positivity does not show the features of viable tumor cells. This positivity likely represents either dying tumor cells (possibly apoptotic cells), characterized by eosinophilic bodies lacking normal nuclei, or macrophages with phagocytosed tumor products. Usually, these cells are single and not in small, cohesive groups. The decision to allocate nodes to this category requires careful comparison of the serial H&E-stained section and the immunocytochemical preparation.
  • Stage 5 tumor: The sample is negative for tumor at all stages.

Another histopathologic staging system divides findings into three categories, [16] which have shown progressively worsening disease-free and overall survival, [14] as follows:

  • Isolated tumor cells: Isolated tumor cells or small clusters
  • Micrometastasis: Lymph node infiltration by tumor less than 2 mm in diameter
  • Macrometastasis: Lymph node infiltration by tumor greater than 2 mm in diameter
Previous
Next:

Approach After Staging

If any lymph node contains a viable tumor (ie, stages 1-3 according to the pathology code description) either based on routine histology studies or based on immunohistochemistry and multiple sectioning, the patient undergoes a completion dissection of the neck. Perform the dissection of the neck within 4 weeks of the SLN biopsy, and begin any adjuvant radiotherapy within 6 weeks of the dissection. Do not administer radiotherapy prior to a neck dissection.

For tumors in stage 4 or 5 according to the pathology code description, no further treatment to the neck is required and no prophylactic neck radiotherapy or additional surgery is necessary.

The current treatment for patients with squamous cell carcinoma (SCC) includes a proper diagnosis based on a high level of consideration and examination, with subsequent staging and development of a treatment paradigm. A treatment program of surgery, radiation, or chemotherapy is best developed by an oncology team that includes surgeons, radiation and medical oncologists, and rehabilitative specialists who all have significant experience in the care of patients with cancer involving the head and the neck. By using this approach, new protocols and surgical options can be appropriately offered to those patients with advanced cancers.

Previous
Next:

Long-Term Monitoring

Patients are seen every 3 months for the first year, every 4 months for the following 2 years, and every 6 months until 5 years following SLN biopsy (SNLB). At any stage, if nodal disease is detected, patients are able to undergo further surgery.

Previous
Next:

Conclusion

SNLB for head and neck squamous cell carcinomas (HNSCCs) is assuming a growing role in the management of early-stage patients. Particularly, those with T1-2 and even early T3 tumors may benefit from the procedure since the rate of occult lymph node metastases in this group is much lower than in those with more advanced tumors. The accuracy of identification and false-negative rates of the procedure are good, but if there is concern by the surgeon performing the procedure that the node is difficult to locate (ie, lymphoscintigraphy findings are unclear or it is difficult to identify in the operating room), a formal neck dissection should be performed. SLNB will probably play an increasing role in the management of early-stage aerodigestive SCC and cutaneous HNSCC in the future as it gains general acceptance.

Previous