[Diseases of the Thymus in domestic mammals: Significance and diagnosis].

In contrast to human medicine, thymic disorders receive little attention as differential diagnoses in veterinary medicine. The aim of this overview is to provide information on the current state of knowledge concerning the topographical anatomy, physiological development, and involution, function, and diseases of the thymus as well as the diagnosis of thymic disorders in various domestic mammals. Therefore, literature on this topic was searched and summarized. The anatomical extent and developmental/involutionary processes differ significantly from species to species. The thymus reaches its maximum size at the beginning of sexual maturity whereas it is largely absent or persists in mere residual form in adult animals. Dogs and goats represent an exception, as functional thymus tissue may also be found in adults. Imaging is often difficult, depending on the size of the animal and the location of the organ. Due to the poor visualization and mostly unspecific clinical signs, disorders of the thymus pose a diagnostic challenge. The thymus may change in size and structure in response to stress or disease. This can lead to impaired immune function and subsequently to infectious diseases. Neoplasia of the thymus has been widely described in domestic mammals. Most reports are found for dogs and goats. Clinical signs usually appear when the tumor becomes space-occupying due to its size or they become apparent in consequence to the occurrence of paraneoplastic syndromes. These may for example include myasthenia gravis. More than 50% of dogs with a thymoma develop a paraneoplastic syndrome. With the availability of modern imaging, assessing the thymus may in future become simpler and may prove useful in evaluating the health status of young animals.