Sentinel node detection and definition may depend on the imaging agent and timing

Purpose: Two cases of sentinel lymph node imaging are presented in which the results are exceptions to what the literature generally defines as sentinel lymph nodes. In one case, Tc-99m antimony trisulfide colloid produced significantly different results than did Tc-99m tin colloid. In the second case, the results bring into question the definition of a sentinel node as the first in a lymphatic drainage pathway. Materials and Methods: In one patient, lymphoscintigraphy was performed initially using Tc-99m antimony trisulfide colloid injected intradermally around a melanoma excision site. Repeated lymphoscintigraphy 1 month later, 1 hour before sentinel node excision, was done using Tc-99m tin colloid, a larger particle than antimony trisulfide colloid. The second patient, with a melanoma biopsied only, had sentinel node imaging performed using Tc-99m sulfide colloid, a particulate also larger than antimony trisulfide colloid and also 1 hour before sentinel node excision. Results: In the first patient, imaging with the smaller antimony trisulfide colloid showed more lymphatic pathways and more sentinel nodes than with tin colloid. In the second patient, the first focus of retention of the imaging agent in the lymphatic pathway seen showed less intense accumulation than the next focus in the pathway, contrary to published reports that the sentinel node shows more intense accumulation than do nodes further downstream in a lymphatic pathway. Conclusions: There are exceptions to published characteristics of sentinel node lymphoscintigraphy, so care must be exercised in localizing sentinel nodes.