Thymomas in rabbits

Neoplastic disease affecting respiratory function is anecdotally encountered more rarely in small mammal species. Early recognition can be challenging in prey species as clinical signs may be mild for most of the disease process until the animal is severely compromised. Similarly, diagnosis can be more challenging in small mammals as a result of factors such as owner finance and compliance leading to restraint of diagnostic modalities. This article will explore clinical signs, diagnosis, treatment options and nursing interventions associated with thymomas in rabbits.

The thymus is the first of the lymphoid organs to be formed during embryonic development. As in other mammals, the rabbit thymus provides the body with the T-cell population of lymphocytes. In most mammals the thymus regresses during ageing into adulthood as production of lymphocytes is dominated by other immune tissues (Harris et al, 2015).

In the rabbit, the thymus remains large throughout life and lies cranioventral to the heart, extending into the thoracic inlet. It is visible on normal thoracic radiographs. Tumour formation originates from abnormal epithelial cell division. Tumours of the thymus can be malignant (malignant thymoma or thymic carcinoma/lymphoma) and metastasise to other organs causing systemic disease. However, usually in rabbits thymomas behave in a benign fashion. This means they are slow growing and rarely metastasise out-with the thoracic cavity, but can be locally invasive and may cause pleural dissemination (Morrisey and McEntee, 2005).