Carbon dye as an adjunct to isosulfan blue dye for sentinel lymph node dissection

Background. The success of intraoperative lymphatic mapping depends on accurate identification of the sentinel node. We hypothesized that a carbon particle suspension would allow histopathologic confirmation of the sentinel lymph node through deposition of carbon within that node. Methods. An animal model was used to compare the lymphatic mapping accuracy of carbon dye with that of isosulfan blue dye, the standard agent for intraoperative visualization of the sentinel lymph node. Twenty-two rats underwent lymphatic mapping in each distal lower extremity with various combinations of carbon dye and isosulfan blue dye. All stained (blue or black) nodes in the inguinal drainage basin were removed for pathologic analysis, including carbon particle analysis. A meticulous search identified all nonstained (nonsentinel) nodes in the same basin. These nonsentinel nodes were examined for carbon particles by light microscopy. Dermal diffusion of mapping agents at the injection site was also recorded. Animals were then observed for 28 days to assess the toxicity of mapping agents. Results. Although isosulfan, blue dye and full-strength carbon dye each stained all sentinel nodes, the latter obscured histologic detail. The combination of 2.5% carbon dye, 7.5% saline solution, and 90% isosulfan Blue dye also stained all sentinel nodes; carbon particles were seen on light microscopy in all 13 stained nodes and did not interfere with histologic evaluation. No unstained node contained carbon particles, although the number of nonsentinel nodes was small. Carbon dye exhibited significantly less intradermal diffusion than isosulfan blue dye, but the carbon left a permanent mark on the skin. No toxicity or side effect associated with the use of carbon dye was observed. Conclusion. Carbon dye allows histopathologic confirmation of sentinel lymph nodes identified by isosulfan blue dye.