The aim of the study was to determine whether the sentinel lymph node (SLN) can be accurately detected in cutaneous melanoma patients when the injection distance from the tumor site is expanded.
Methods: In 100 patients with cutaneous melanoma, lymphoscintigraphy was performed twice. First, we injected 37 MBq (99m)Tc nanocolloid intracutaneously at a 2- to 5-mm distance from either the melanoma or the biopsy scar. The injection was followed by dynamic imaging, which continued until the SLN became visible. On another day, we repeated the investigation, injecting the radiopharmaceutical intracutaneously exactly 10 mm from the previous injection site. The detected SLNs of both investigations were compared to determine the number and location of SLNs for each patient.
Results: The SLN identification rate was 94% with close injection and 100% with 10-mm-distant injection. All SLNs detected with close injection were visible with distant injection. In 84 of 100 patients, the images of both investigations showed the same number and location of SLNs. In the remaining 16 patients, an additional SLN was detected with the distant injection.
Conclusion: The reproducibility of lymphoscintigraphy using different injection distances was 84%. The discordance in the remaining 16% was caused by detection of a lymph node in addition to the original SLN with distant injection. Diagnostic excision of the primary tumor before lymphoscintigraphy was possible without preventing detection of the original SLN. However, in 16% of our patients, excision of an additional lymph node had to be considered when lymphoscintigraphy was performed after diagnostic excision.