How to find sentinel lymph nodes in dogs with thyroid cancer

Abstract

OBJECTIVE: The aim of this study was to develop and describe pre- and intra-operative sentinel lymph node (SLN) mapping techniques in dogs with thyroid carcinoma. STUDY DESIGN: A prospective, pilot clinical trial was performed. ANIMALS: Six client-owned dogs with unilateral thyroid carcinoma and no overtly metastatic locoregional lymph nodes (LNs) were enrolled. METHODS: All dogs underwent preoperative indirect computed tomography (CT)-lymphography (CTL) with peritumoral iohexol injection and intraoperative SLN mapping with peritumoral injection of a visible dye (methylene blue [MB]) and near-infrared (NIR) fluorescent dye (indocyanine green [ICG]). Subsequent LN extirpation and routine thyroidectomy were performed. All excised tissues were evaluated histologically. RESULTS: Pre- and intra-operative SLN mapping identified at least one SLN in all dogs. A median of one SLN (range, 1-2) was identified on both CTL and intraoperative SLN mapping. Identified SLNs included medial retropharyngeal, cranial deep cervical, and superficial cervical LNs. Variability between pre- and intra-operative SLN findings occurred in 3/6 dogs. A median of two LNs (range, 1-3) were extirpated for each dog. Metastatic carcinoma was diagnosed in extirpated LNs in 2/6 dogs and 3/12 extirpated LNs. CONCLUSION: In this pilot study, preoperative CTL and intraoperative MB and ICG/NIR allowed for identification of SLNs in dogs with thyroid carcinoma. CLINICAL SIGNIFICANCE: Sentinel lymph nodes were identified and extirpated using the described techniques, with nodal metastasis identified in a subset of these dogs due to SLN mapping. Large-scale, powered studies are needed to accurately determine the incidence and prognostic significance of nodal metastasis identified by SLN mapping and extirpation in dogs with thyroid carcinoma.