Reliability of lymphoscintigraphy in indicating the number of sentinel nodes in melanoma patients

Background: This study was undertaken to establish the reliability of lymphoscintigraphy in indicating the number of sentinel nodes in patients with melanoma. Methods: Lymphoscintigraphy was performed with dynamic imaging after injection of 60 MBq Tc-99m-nanocolloid (1.6 mCi) and static imaging after 2 hours in 200 patients with clinically localized primary melanoma of the skin. The following day, sentinel nodes were retrieved with the blue dye technique and a gamma detection probe (Neoprobe 1000/1500). The discrepancies between the number of sentinel nodes indicated by lymphoscintigraphy and the actual number of sentinel nodes as established by the surgeon were evaluated. Results: Lymphoscintigraphy showed drainage to 393 sentinel nodes in 255 lymphatic fields in 199 patients. In 48 lymphatic fields (19%) in 46 patients (23%), the number of sentinel nodes was different from the number that was visualized with scintigraphy. Additional sentinel nodes were found by the surgeon because a lymphatic vessel was not seen on the lymphoscintigraphy (43%), because a sentinel node was nor visualized separately from other hot nodes or vessels or the injection site (36%), or because a sentinel node was blue and not hot (4%). Fewer sentinel nodes were found than suggested by scintigraphy because a lymphangioma was mistaken for a sentinel node (4%) or because a single elongated node was depicted as two hot spots (6%). Conclusions: Although lymphoscintigraphy is indispensable for lymphatic mapping, the predicted number of sentinel nodes is accurate in only 81% of lymph node fields. The limited discriminating power of the gamma camera is an important cause of discrepancies.