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The Sentinel Node definition

Romeo Giuli MD, resident.
School of General and Emergency Surgery.
University of Siena.   Italy.

August 2001.     Review Article.     To the updating

The sentinel node hypothesis states that the histopathologic status of the first node on the lymphatic drainage pathway from a primary tumor reflects the tumour status of the entire lymphatic drainage basin.
Underlying this hypothesis is the assumption that the surgeon can correctly and consistently identify this node ( 2 ).

The anatomical definition of the sentinel node as the lymph node closest to the primary lesion does not take into consideration the physiology of lymph drainage: the node closest to the primary tumour is the first one to be involved only when it receives direct drainage from the injection site.

Some investigators in the field of the nuclear medicine define the sentinel lymph node as the first lymph node that becomes visible on the lymphoscintigraphic images. But sometimes there are two or more lymphatic channels originating in the region of the primary tumour and running to different lymph nodes. All this first tier nodes should be harvested and examined by the pathologist. One may be depicted on the scintigraphy images before the other, this does not imply that the other nodes are not sentinel nodes.

There are some reasons not to use the brightness of a node on the scintigram to decide whether or not a lymph node is a sentinel node. The amount of tracer that is accumulated by a node not only depends on its position in the drainage order but also on the number of lymphatic channels that enter the node, on the size of lymph node, on macrophage avidity for the tracer, and on parameters such as lymphatic flow rate. Lymph flow depends on factors such as physical exercise, medication, massaging of injection site and hydratation of the patient.

Moreover the brightness of a node depends on the amount of radionuclide in that node but also on its distance to the gamma camera. And some of the tracer may pass through the first tier lymph node and lodge in secondary nodes that are not at risk of harbouring metastatic disease.

Similarly if we assume that a sentinel lymph node is a blue node, (definition based on use of the vital dye), we must remember that some of the tracer may pass through the first tier lymph node and stain secondary nodes. The ingress of lymph may be obstructed or the lymphatic flow may have stopped because the duct has suffered damage upstream.

Although good results have been achieved using blue dye or a probe alone, the most practical approach is probably to use all the available detection techniques ( 1, 7, 8, 9 ).
Ultimately individual surgeons must choose the technique that they are most comfortable with, and with which they can document success rates comparable with those reported in the literature ( 4 ).

Techniques of intraoperative lymphatic mapping and SLND using dye, tracer, or both have high success rates in the hands of experienced investigators, but their routine and widespread use awaits resolution of questions about the timing, dose, and type of radioactive tracer; the optimal lymphatic mapping technique; indications and contraindications for SLND; and certification of qualified surgeon, pathologists, and nuclear medicine physicians ( 2 ).


1) Omgo E Nieweg, Pieter J Tanis, and Bin B R Kroon. The definition of a sentinel node. Annals of Surgical Oncology 2001, 8 (6): 538-541.

2) Eddy C Hsueh, Roderick R Turner, Armando E Giuliano. Lymphoscintgraph and lymphatic mapping for identification of sentinel lymph nodes. World J Surg. 25, 794-797, 2001.

3) Rache M Simmons. Review of sentinel lymph node credentialing: how many cases are enough? Journal of the American College of Surgeons vol 193, n2, August 2001, 206-209.

4) Monica Morrow et al. Learning sentinel node biopsy: results of a prospective randomized trial of two techniques. Surgery 1999; 126: 714-22.

5) Keshtgar MRS, Waddington WA, Lakhani SR, Ell PJ. The sentinel node in surgical oncology. Berlin: Springer, 1999.

6) Thompson JF, Uren RF. What is a sentinel lymph node? Eur J Surg Oncol 2000; 26: 103-4.

7) R J Rosser, Palm Springs. Sentinel lymph nodes and postinjection massage: it is premature to reject caution. Journal of the American College of Surgeons vol 193, n2, August 2001, 338.

8) C E Cox. Reply. Journal of the American College of Surgeons vol 193, n2, August 2001, 338.

9) Bass SS et al. The effects of postinjection massage on the sensitivity of lymphatic mapping in breast cancer. J Am Coll Surg 2001; 192: 9-16.

10) Rosser RJ. A point of view: trauma is the cause of occult micrometastatic breast cancer in sentinel axillary lymph nodes. The breast J 2000; 6:209-212.

11) Tafra L et al. Multi-center trial of sentinel node biopsy for beast cancer using bot technetium sufur colloid and isosulfan blue dye. Ann Surg 2001; 233: 51-59.

12) Morton DL. Intraoperative lymphatic mapping and sentinel lymphadenectomy: community standard care or clinical investigation? Cancer J Sci Am 1997; 3: 328-30.

13) Krag D et al. The sentinel node in breast cancer : a multicenter validation study. N Engl J Med 1998; 337: 941-6.

14) O' Hea, BJ et al.Sentinel lymph node biopsy in breast cancer: initial experience at Memorial Sloan Kettering Cancer Center. J Am Coll surg. 186: 423, 1998.

15) Giuliano AE et al. Prospective observational study of sentinel lymphadenectomy without further axillary dissection in patients with sentinel node- negative breast cancer. J Clin Oncol 18: 2553, 2000.

16) Veronesi U et al. Sentinel-node biopsy to avoid axillary dissection in breast cancer with clinically negative lymph nodes. Lancet 349: 864, 1997.

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