Pre-contrast computed tomography reveals distinct characteristics and anatomical distribution of presumably lymphomatous lymph nodes in canine multicentric lymphoma.

Background and Aim: Canine multicentric lymphoma (CML) is one of the most common hematopoietic neoplasms in dogs and is characterized by generalized lymphadenopathy involving peripheral and visceral lymph nodes. Accurate identification of lymphomatous lymph nodes (LLNs) is essential for diagnosis, staging, and monitoring treatment response. Conventional diagnostic methods such as palpation, radiography, and ultrasound may be limited by anatomical superimposition, restricted visualization of deep structures, and operator dependency. Computed tomography (CT) provides high-resolution, whole-body imaging and may allow more reliable differentiation between abnormal and normal lymph nodes. However, information regarding pre-contrast CT characteristics of LLNs in dogs remains limited. This study aimed to describe the anatomical distribution of presumably lymphomatous lymph nodes and to evaluate pre-contrast CT parameters, including size, morphology, and attenuation values, for distinguishing LLNs from normal lymph nodes (NLNs). Materials and Methods: This retrospective, multicenter observational study evaluated medical records and pre-contrast CT images of dogs examined between February 2014 and February 2024 at two veterinary diagnostic centers in Bangkok, Thailand. The study included two groups: dogs diagnosed with CML confirmed by cytologic or histopathologic examination and dogs without lymph node-related diseases. A total of 99 presumably LLNs from nine dogs with CML and 138 NLNs from nine control dogs were analyzed. CT parameters assessed included lymph node size (width, depth, length, and depth-to-length ratio), nodal appearance (homogeneity, contour, shape, and hilar fat), and CT attenuation values of lymph nodes and perinodal fat. Statistical comparisons were performed using independent t-tests, Mann-Whitney U tests, and chi-square tests. Receiver operating characteristic analysis was used to determine the optimal cutoff value for CT attenuation. Results: Peripheral lymph nodes, particularly the mandibular, superficial inguinal, and medial iliac nodes, were most frequently affected in CML. Presumably LLNs were significantly larger in width, depth, and length than NLNs (p < 0.001), but the depth-to-length ratio did not differ significantly. LLNs more commonly exhibited heterogeneous attenuation, irregular contours, and absence of hilar fat (p < 0.001). CT attenuation values of both lymph nodes and perinodal fat were significantly higher in LLNs than in NLNs. A cutoff value greater than 31.37 Hounsfield units differentiated LLNs from NLNs with 82.8% sensitivity and 70.8% specificity. Conclusion: Pre-contrast CT is a valuable diagnostic tool for identifying LLN in dogs with multicentric lymphoma. Increased nodal size, irregular morphology, absence of hilar fat, and higher CT attenuation values, particularly a cutoff value above 31.37 Hounsfield units, can assist in differentiating abnormal from normal lymph nodes. These findings may improve diagnostic accuracy, guide biopsy site selection, and support monitoring of treatment response in canine lymphoma.