Computed tomographic evaluation of canine hepatic lymph nodes: Establishment of aorta-normalized dimension ratio cutoff values for differentiating normal from abnormal conditions.

Background and Aim: Hepatic lymph nodes (HLNs) drain lymph from the liver, gallbladder, pancreas, stomach, and duodenum. Enlargement of these nodes may indicate pathology in those organs, but objective, breed-independent computed tomography (CT)-based size criteria have not been established. This study aimed to determine quantitative cutoff values for HLN dimensions normalized to aortic diameter (Ao) to differentiate normal from abnormal HLNs in dogs. Materials and Methods: This retrospective study analyzed contrast-enhanced abdominal CT scans (slice thickness <1.5 mm) from 84 dogs older than 1 year, examined between March 2016 and November 2022. Dogs were divided into two groups: no targeted organ abnormalities (26 dogs; 46 HLNs) or presence of targeted organ abnormalities in the liver, gallbladder, pancreas, stomach, duodenum, or combinations (58 dogs; 89 HLNs), based on clinical, laboratory, and imaging findings. Using multiplanar reconstruction, the maximum length (cranio-caudal), width (latero-lateral), and height (dorso-ventral) of each HLN were measured and divided by the Ao measured at the same level. Parameters were compared between groups using Mann-Whitney U tests. Receiver operating characteristic curves were used to identify optimal cutoff values, sensitivity, specificity, and area under the curve (AUC). Results: HLN dimensions and dimension-to-Ao ratios were significantly larger in dogs with targeted organ abnormalities (all p < 0.001). Mean width-to-Ao ratio, length-to-Ao ratio, and height-to-Ao ratio were 0.7 ± 0.3, 1.4 ± 0.7, and 0.6 ± 0.3 in the normal group versus 1.2 ± 1.2, 2.0 ± 0.8, and 0.8 ± 0.4 in the abnormal group, respectively. The width-to-Ao ratio showed the highest diagnostic performance (AUC = 0.76, 95% confidence interval: 0.69-0.85; p < 0.0001), with an optimal cutoff of ≥ 0.75 (sensitivity 70%, specificity 67%). Height-to-Ao ratio cutoff was ≥ 0.615 (AUC = 0.70), and length-to-Ao ratio cutoff was ≥ 1.58 (AUC = 0.70). Conclusion: Ao-normalized HLN dimension ratios provide an objective, breed- and body-size-independent criterion for CT evaluation of canine hepatic lymph nodes. A width-to-Ao ratio ≥ 0.75 offers the best balance of sensitivity and specificity for identifying HLN abnormalities suggestive of targeted organ pathology. These cutoff values support non-invasive CT-based assessment but should be interpreted with clinical and laboratory findings; histopathology remains essential for definitive diagnosis.