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

Purpose: Two cases of sentinel lymph node imaging are presented in which th e results are exceptions to what the literature generally defines as sentin el lymph nodes. In one case, Tc-99m antimony trisulfide colloid produced si gnificantly different results than did Tc-99m tin colloid. In the second ca se, the results bring into question the definition of a sentinel node as th e first in a lymphatic drainage pathway. Materials and Methods: In one patient, lymphoscintigraphy was performed ini tially using Tc-99m antimony trisulfide colloid injected intradermally arou nd a melanoma excision site. Repeated lymphoscintigraphy 1 month later, 1 h our before sentinel node excision, was done using Tc-99m tin colloid, a lar ger particle than antimony trisulfide colloid. The second patient, with a m elanoma biopsied only, had sentinel node imaging performed using Tc-99m sul fide colloid, a particulate also larger than antimony trisulfide colloid an d 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 t in colloid. In the second patient, the first focus of retention of the imag ing agent in the lymphatic pathway seen showed less intense accumulation th an the next focus in the pathway, contrary to published reports that the se ntinel node shows more intense accumulation than do nodes further downstrea m in a lymphatic pathway. Conclusions: There are exceptions to published characteristics of sentinel node lymphoscintigraphy, so care must be exercised in localizing sentinel n odes.