Nodal radioactivity after lymphoscintigraphy as a guide to sentinel node-positivity in melanoma patients

Objective: To determine how often the sentinel node (SN) with the highest gamma count after lymphoscintigraphy was metastasis-free in SN-positive melanoma patients.

Background: SN biopsy (SNB) is a standard staging procedure for patients with primary cutaneous melanoma. After pre-operative radiotracer injection, intra-operative gamma counts are used, with blue dye localization, to guide SN retrieval. Sometimes only the “hottest” nodes are removed, but the reliability of predicting SN-positivity on the basis of a node’s gamma count is uncertain.

Methods: Patients who had a SNB and in whom ≥2 SNs were removed, at least one of which contained metastatic melanoma, were identified from an institutional database. After preoperative lymphoscintigraphy using Tc-99m antimony sulfide colloid injected at the primary melanoma site, residual radioactivity in SNs was used to assist their intra-operative localization. Gamma counts were recorded for all SNs that were removed, and correlated with SN-positivity on subsequent histopathology.

Results: In 550 of 715 patients with complete data for analysis the “hottest” SN contained metastatic melanoma, but the remaining 165 patients (23 %) had metastatic disease exclusively in a SN with a lower gamma count.

Conclusions: For accurate intraoperative identification of SNs containing metastatic melanoma, gamma counts may be unreliable. The key to accuracy is high-quality lymphoscintigraphy, ideally with SPECT-CT imaging, for precise preoperative identification and localization of SNs. Use of a gamma-detection probe intraoperatively will assist in the search for these pre-operatively identified SNs, but removal of only the “hottest” node will not reliably indicate whether regional node metastasis has occurred.