Contrast-enhanced CT predictors of lymph nodal metastasis in dogs with oral melanoma

Canine oral melanoma (OM) has highly aggressive behavior, with frequent local metastasis. Computed tomography 3D volumetric analysis is an accurate predictor of lymph node (LN) metastasis of oral cancers in humans but whether this is true for dogs with OM is unknown. In this retrospective observational study, CT imaging was used to assess mandibular and retropharyngeal lymphocenter (LC) changes in dogs with nodal metastatic (n = 12) and non-metastatic (n = 10) OM, then these findings were compared with those of healthy control dogs (n = 11). Using commercial software (Analyze, Biomedical Imaging Resource), lymphocenters were defined as regions of interest. LC voxels, area (mm² ), volume (mm³ ), and degree of attenuation (HU) were compared between groups. Mandibular lymphocenter (MLC) metastasis was present in 12 of 22 (54.5%) dogs; no dogs had confirmed retropharyngeal lymphocenter (RLC) metastasis. Mandibular lymphocenter volume was significantly different between positive and negative LCs (median 2221 and 1048 mm³ , respectively, P = 0.008), and between positive and control LCs (median 880 mm³ , P < 0.01). There was no evidence of a significant difference in voxel number or attenuation between groups. Mandibular lymphocenter volume moderately discriminated for metastatic status (AUC 0.754 [95% CI = 0.572-0.894, P = 0.02]), with a positive predictive value of 57.1% (95% CI = 0.389-0.754). Adjusting for patient weight did not improve discrimination (AUC = 0.659 (95% CI = 0.439-0.879, P = 0.13]). In conclusion, these findings suggest 3D CT volume measurement of MLC can predict nodal metastasis in dogs with OM and shows promise but further research, perhaps in combination with other modalities, is required to improve accuracy.