A combination of pre‐ and intraoperative techniques identifies sentinel lymph nodes in dogs with thyroid carcinoma: A pilot study

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.