Utilization of indocyanine green for intraoperative sentinel lymph node mapping in canine mammary tumors

Abstract

Accurate staging by sentinel lymph node (SLN) biopsy is essential for improving prognostic outcomes of canine mammary tumors (CMT). Indocyanine green near-infrared fluorescence (ICG-NIRF) imaging offers a novel real-time approach for SLN mapping, potentially enhancing the precision of surgical SLN biopsies. This study evaluated the effectiveness of transcutaneous ICG-NIRF imaging in identifying lymphatic drainage pathways and SLNs in CMT and determined the optimal ICG concentration for visualizing lymphatic channels and SLNs. We hypothesized that transcutaneous ICG-NIRF imaging effectively highlights both lymphatic channels and SLNs, facilitating accurate SLN biopsies. This study included 24 female dogs with cytologically diagnosed malignant CMT, from September 2023 to April 2024. ICG was injected peritumorally (concentrations: 0.5, 1.0, and 2.5 mg/mL). NIRF imaging was conducted intraoperatively to visualize lymphatic drainage and identify SLNs. Data on signal-to-background ratio of lymphatic drainage and SLN and operation time were collected and analyzed using ANOVA and post-hoc Tukey tests. The detection rate of SLNs using ICG-NIRF was 94.4% (34/36). Highest LN fluorescence (p = 0.030) and shortest operation time (p = 0.002) were yielded by 1.0 mg/mL ICG, with minimal false-negative rates (0%, 0/18). ICG-NIRF imaging enhances the accuracy of sentinel lymph node mapping in CMT by enabling real-time visualization of lymphatic drainage, optimizing lymph node biopsy selection, and improving surgical precision, thereby contributing to more accurate tumor staging and better prognostic assessment.

Keywords: Canine; ICG-NIRF; Lymphatic drainage; Mammary tumors; Optimal ICG concentration; SLN mapping.

Fig. 1

Indocyanine green (ICG) near-infrared fluorescent images of lymphatic drainage (arrowhead) and sentinel lymph node (arrow) in canine mammary tumor. Three different concentrations of ICG were used for sentinel lymph node mapping of canine mammary tumors: (a, b) 2.5 mg/mL, (c, d) 1.0 mg/mL, and (e, f) 0.5 mg/mL.

Fig. 2

(a) True-positive lymphatic drainage (arrowhead) and (b) false-negative sentinel lymph node (arrow) of the canine mammary tumor. The lymph node did not exhibit fluorescence, but the lymphatic drainage was sufficiently clear to guide the sentinel lymph node biopsy. This effect was observed in case no. 5, which has used an indocyanine green concentration of 2.5 mg/mL.

Fig. 3

A graph presenting the comparative analysis of operation time, lymphatic duct signal-to-background ratio (SBR), and lymph node SBR in canine mammary tumors using various concentrations of indocyanine green (ICG) (0.5, 1.0, and 2.5 mg/mL). The data were analyzed using ANOVA and post-hoc Tukey tests. (a) The operation time for the 0.5 mg/mL ICG concentration group was significantly shorter compared to the 2.5 mg/mL concentration group (p = 0.002). (b) The lymphatic duct SBR was significantly greater in both the 2.5 mg/mL and 1.0 mg/mL concentration groups compared to the 0.5 mg/mL group (p < 0.001 and p = 0.003, respectively). (c) The 1.0 mg/mL ICG concentration resulted in the highest lymph node SBR (mean, 10.9 ± 4.8; 95% confidence interval, 6.9–14.9), which was significantly higher than that of the 2.5 mg/mL concentration (p = 0.030).