Computed Tomographic Features of Thymus Gland in Dogs: Correlation with Age, Gender, Breed and Body Fat Content

: Background: The thymus gland is the first lymphoid organ formed to regulate a newborn's immunity. It reaches its maximum size during puberty, after which it undergoes an atrophic procedure called involution, but its ability to grow again in response to some stresses, such as infections, neoplasia, surgeries, chemotherapy, and radiotherapy is maintained. There is not any comprehensive study on computed tomographic features of thymus gland in dogs. So, the goal of the present study is to achieve some information about thymus gland using computed tomography as a non-invasive method. Methods: One hundred and fifty dogs classified in 5 age groups and 2 breed groups were entered to this study and the thymus gland was evaluated using 2-slice computed tomography machine. The inclusion criteria for the present study were having normal complete blood count, plain and post-contrast CT scan examination of thoracic region and no history of neoplasia, chemotherapy or radiotherapy. The visibility, density, enhancement, grade, size, volume, shape, borders and lateralization of the thymus were evaluated and statistical analysis were performed. The effect of obesity on thymic grade and volume were also investigated. Results: The visibility, density, dorsal length, volume and grade decreased with increasing age. The thymic shape and lateralization were mostly wedge-shaped and left sided respectively. The borders became concave with aging and increasing body fat content caused to increase fatty degeneration of thymus. Conclusions: Declining of thymic density, grade, size and volume with aging was related to thymic involution and fatty degeneration was accelerated by increasing body fat content. Females and Males were different only in thymic shape and small and large breeds were different only in thymic volume. The thymus was visible in some geriatric dogs with no underlying disease. We hope that the present work can be used by radiologists in reading thoracic computed tomography but investigation of thymic characteristics in dogs with neoplasia and history of chemotherapy, radiotherapy and thoracic surgeries can complete this study.