Localizing the sentinel node in cutaneous melanoma: Gamma probe detection versus blue dye

Background: Sentinel node (SN) biopsy can be used to select patients with melanoma for therapeutic lymphadenectomy. We investigated the value of two methods to locate the SN: patent blue dye (PBD) and gamma probe detection of Tc-99m-nanocolloid. Methods: One hundred ten patients with cutaneous melanoma were studied, Lymphoscintigraphy with Tc-99m-nanocolloid was performed to determine the position of the SN, Before operation, PBD was injected at the same site as the radiopharmaceutical. When a blue node was identified intraoperatively, its radioactivity level was measured with the probe. In the absence of blue coloration, the probe was used to trace the SN. Results: Scintigrams visualized a total of 219 SNs in 141 basins. Eight SNs were not explored. One SN was not found. The remaining 210 and 27 additional intraoperatively identified SNs were excised. From the total of 237 removed SNs, 200 (84%) were found using PBD only. All 37 nodes that were not found with the PBD were localized with the probe so that the probe combined with PBD identified 99.5% of all SNs. In 23 patients the SN contained tumor. In three patients the SN was false-negative for metastasis. Conclusion: The gamma probe together with PBD can identify more SNs (99.5%) than lymphatic mapping with PBD alone (84%).