Superficial sentinel lymph node biopsy in 23 tumor-bearing dogs: pre- and intra-operative intra-patient comparison between lymphoscintigraphy and near-infrared fluorescence

Near Infrared Fluorescence (NIRF) with Indocyanine Green (ICG) can replace and improve lymphoscintigraphy (LPS) during sentinel lymph node (SLN) biopsy in human [1-3]. The paucity of data in veterinary medicine [4] led us to compare LPS and NIRF into sentinel lymphocentrum (SLC) mapping and SLN extirpation in canine patients bearing different solid tumors, during the first 6 month of a Ph.D. project. Tumor-bearing dogs were prospectively enrolled for SLN excision guided by handheld gamma probe (HGP) and NIRF. The same surgeon performe all the procedures. Tc99m and ICG were injected peritumorally; for standard practice, methylene blue was also injected. Data collected were: tumor histotype, histological nodal status, number of SLCs, correspondence with the regional lymphocentrum, number of SLNs and SLN detection rate. Intrapatient comparison between LPS and NIRF performance was recorded in pre -operative phase (planar LPS and NIRF during mapping and SLC detection; HGP and NIRF during incisional site detection) and intra-operative phase (HGP and NIRF during SLC surgical exploration for SLNs excision). In the latter phase, SLN radioactivity, fluorescence, blue dyeing, and the surgeon’s perception in helping the SLN detection were recorded. Forty-four SLNs were excised from 32 SLCs, in 23 dogs with 27 tumors (21 mast cell tumors, 2 soft tissue sarcomas, one oral melanoma and 3 mammary tumors). The SLN detection rate of the 2 techniques combined was 100%. In 59% of cases, SLC did not correspond to the regional lymphocentrum. Pre-operatively planar LPS and NIRF failed mapping respectively in one and two tumors. In 2 tumors, both HGP and NIRF failed in the incisional site detection due to “shine through” effect. Radioactivity, fluorescence and blue dying were found respectively in 40, 41 and 39 of 44 excised SLNs. Surgeon’s perception in SLNs detection was: HGP was better in 21/44, NIRF was better in 8/44 SLNs, and no differences in 15/44. In 11/11 axillary SLCs, the HGP was judged more useful than NIRF. In other regions, the 2 techniques had equal performance. Ten (45%) dogs had histological nodal metastasis. In conclusion, the performance during the pre-operative mapping phase for superficial SLC detection was equal in LPS and NIRF. When considering SLCs incisional site detection and their surgical exploration, NIRF performance was negatively influenced by SLC anatomical location (such as in the axillary region) and deeper lymphatic networks.