The first lymph node draining a tumor site corresponds to the sentinel node, which is the first to be involved with metastatic disease due to lymphatic spread ^1,2. Thus, histopathologic evaluation of this lymph node can be highly predictive. The sentinel node study has become a routine staging method for melanoma patients as a result of the introduction of the handheld probes, which enable the precise intraoperative location of one, even very small, radioactive node. ³

This report presents three cases of unexpected location of the sentinel node.

All patients were injected intradermally with Tc99m-Dextran (CGM-Nuclear), 0.5 – 1 mCi (18 - 37 MBq) around the primary tumor site. Gammacamera images and external probe detection identified the sentinel node between 30 – 120 min after injection in all patients. All three patients were operated between 2 and 3 hours after the radioisotope injection and biopsy specimen imaging was done to confirm sentinel node excision.

Case 1

AM, 43 year old male with a melanoma in the left supraclavicular space. One sentinel node was found in the suprasternal space, corresponding to a pretracheal node. This node was found to have metastasis on histopathologic evaluation.

In spite of the absence of other sentinel nodes by lymphoscintigraphy, an elective axillary lymph node dissection was performed. All axillary nodes were found to be negative for metastasis. Fig.1

Case 2

TO, 55 year old male with a melanoma in the anterior aspect of the right arm was found to have only one lymphatic path directed to sentinel node in the right infraclavicular space. At surgery, one small, superficial node was excised at that location. Axillary lymph node excision was done as well. The infraclavicular node was histologically negative for tumor, and so were also all axillary nodes. Fig.2

Case 3

JB, 37 year old female with a melanoma (Clark IV, Breslow high risk) in the posterior aspect of the left ankle. Lymphoscintigraphy showed initially an external inguinal node and later another node became visible at the middle third of the thigh. This node was located closest to the original lesion but, because three lymphatic paths were visible (two of them bypassing that node), both nodes were considered as sentinel nodes. They were located by means of the probe and excised. Fig.3

This report of 3 melanoma patients demonstrates that the sentinel node location is often unpredictable even for tumors of the limbs. Preoperative lymphoscintigraphy is of crucial importance to help to decide the lymphatic territory to be explored at surgery and achieve a precise staging.

It is also clear that the images of the lymphatic pathways give crucial information, especially when more than one node is visible ⁴. In that case, the decision of how many and which nodes are sentinel nodes can be made based on the flow images. Lymphoscintigraphy has been demonstrated to be a safe and accurate method to identify sentinel node in 96% of melanoma patients. ⁵

In our first patient, the only metastatic node would have been missed if the surgeon had done his routine surgery for that tumor location: the axillary node dissection.

The axillary dissection could have been avoided for the second patient.

In the patient with the melanoma of the ankle, popliteal lymph nodes were not found and the unexpected node in the midtigh could be demonstrated due to the images of the whole lower limb and a long enough imaging time. The presence of this unexpected sentinel node was confirmed by oblique and lateral images accompanied by progressive increase in radioactivity during the lymphoscintigraphy acquisition time.

REFERENCES

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2. Comparison of Blue Dye and Probe-Assisted Intraoperative Lymphatic Mapping in Melanoma to Identify Sentinel Nodes in 100 Lymphatic Basins. Bostick P., Essner R., Glass E., Kelley M., Sarantou JT., Foshag L., Qi K., Morton D. Arch Surg 1999,134:43-49

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