Introduction

In canine oral malignant melanoma (OMM), it is essential to accurately identify the sentinel lymph nodes (SLNs) that receive drainage from the primary tumor at diagnosis. However, the lymphatic pathways in the head are complex, with multiple lymphocentra receiving drainage. We hypothesized that SLNs can be detected using CT lymphography (CTLG).

Methods

Dogs with OMM that had undergone CTLG, excluding cases with distant metastasis, were enrolled. CTLG was performed using the following procedure: first, CT scans, including the primary tumor and the regional lymph nodes, were obtained; second, according to tumor size, approximately 1–2 ml of a 300 mgI/ml iodinated contrast agent was injected around the tumor; finally, CT scans were performed 0, 3, 6, and 9 minutes after injection.

Results

Out of 60 dogs, 59 had their SLNs successfully identified. Thirty-one dogs had a single SLN, and 28 dogs had more than two SLNs. Although the ipsilateral mandibular lymph node (iMLN) was always detected in each dog, the remaining SLN locations in the dogs that had more than two SLNs were inconsistent with the primary tumor location or size. On the univariate analyses, the tumor size and the palate-invading tumor were identified as significant variables associated with the number of SLNs (p=0.003 and <0.001, respectively).

Conclusion

Almost all SLNs were detected by CTLG. Although iMLN should be sampled in all dogs to confirm whether metastasis is present, the possibility that multiple SLNs exist needs to be considered when a larger or palate-invading tumor is discovered.