Sentinel Lymph Node Mapping Identifies Variable Cervical Drainage and Metastatic Nodes Outside Traditional Sampling Sites in Canine Oromaxillofacial Tumours.

Sentinel lymph node mapping (SLNM) has emerged as a key technique to guide decisions regarding nodal extirpation in dogs with oromaxillofacial tumours. The primary aims of this retrospective study were to describe the clinical utility of indirect computed tomographic lymphangiography (ICTL) for SLNM in a large cohort of dogs, characterise variability in SLN drainage patterns by tumour location, and describe the distribution of metastatic lymph nodes (LNs) identified by SLNM guided cytology or pathology. SLN locations, cytology, and available histopathology were reported as descriptive data. ICTL data were evaluated for 77 oromaxillofacial tumours in 74 dogs. A median of 2 SLNs were identified per ICTL dataset with 92% having at least one SLN identified. The ipsilateral mandibular lymphocentrum was the most common drainage basin; however, contralateral or bilateral drainage was frequent, occurring in over 55% of rostral tumours. Lateralized tumours were associated with a higher frequency of ipsilateral mandibular SLN identification compared with non-lateralized tumours (p = 0.0009). Of 68 dogs with malignant tumours, 10 (15%) had LN metastasis. Metastasis occurred in the SLN (n = 8), outside the SLN (n = 1), and in one dog without any identifiable SLNs. In 4 dogs (40%), metastasis extended beyond the ipsilateral lateral MLN; 3 dogs had metastasis exclusively in the medial retropharyngeal LNs. Among dogs with paired cytology and pathology, the false-negative rate of SLN cytology was 6.9%, potentially offering a low-morbidity screening method prior to LN extirpation. Future studies should seek to evaluate how SLNM with guided LN sampling influences patient outcomes, given its clinical feasibility.