Sentinel lymph node mapping with computed tomography lymphangiography and intraoperative methylene blue peritumoral injection has a high detection rate with moderate agreement in dogs with oral neoplasms.

Objective: To investigate the feasibility of indirect CT lymphangiography (CTL) and intraoperative lymphangiography with methylene blue (IOL-MB) for sentinel lymph node (SLN) mapping in canine oral cancer and to report both agreement between the techniques and accuracy of identifying metastatic lymph nodes (LNs).

Methods: This prospective study included 38 client-owned dogs with gross macroscopic or incompletely excised microscopic oral neoplasms. All dogs underwent CTL, IOL-MB, and extirpation of bilateral mandibular and retropharyngeal LNs. The detection rate of SLNs using the combined techniques was evaluated, and agreement between CTL and IOL-MB was assessed.

Results: The combined techniques identified all metastatic cases (4 of 4 dogs, 6 of 6 LNs) and achieved an SLN detection rate of 97.4% (37 of 38 dogs), with moderate agreement between modalities (76.8%; κ = 0.481). Nine cases showed discrepancies between the techniques, including 1 involving a metastatic LN.

Conclusions: CTL and IOL-MB demonstrated moderate agreement and an excellent detection rate for SLNs. With moderate agreement between modalities, our results suggested that the relationship between mapped LNs and true SLNs is not always straightforward.

Clinical relevance: Results of this study suggested that SLN mapping techniques are most effective when there is no evidence of overt clinical LN metastasis. Employing at least 2 modalities is advisable, as metastasis may impact SLN identification rates depending on the technique utilized.