Thymomas are tumors derived from thymic epithelial cells and contain various proportions of benign lymphoid proliferating cells. Located in the ventral cervical region or cranial mediastinum, these tumors are usually well circumscribed and rarely metastasize.1 Thymomas have been reported in several species, including humans, dogs, cats, horses, pigs, cows, and goats.2–7 Considered a rare tumor in most species, thymomas appear to be more common in goats. In a large study8 involving goats submitted for necropsy, thymomas were identified in 9 of 100 (9%) goats with tumors, representing the third most common tumor type. Likewise, in another study,9 thymomas were incidental findings in 17 of 67 (25%) dairy goats > 2 years of age submitted for necropsy.
The clinical importance of thymomas in goats is largely unknown. In dogs, thymomas are typically found in the cranial mediastinum.10 Tumors in this location are often associated with clinical signs and effects, such as pleural effusion, respiratory distress, and sudden death. Myasthenia gravis and megaesophagus are also common in dogs with cranial mediastinal thymomas.1,11 Conversely, in the few reports8,9 of thymomas in goats, these tumors are described as incidental findings at necropsy. This gives the impression that thymomas rarely cause clinical disease even if located in the mediastinum8,9; however, individual case reports12–14 exist of clinical disease in goats attributable to thymomas.
Treatment options for thymomas include tumor excision, radiotherapy, and chemotherapy.7,15,16 Excision is the treatment of choice for humans, with adjunctive radiotherapy used to treat certain subtypes.16 In 20 dogs and cats with thymomas, excision alone resulted in a favorable long-term outcome, with 1-year survival rates of 64% for dogs and 89% for cats.6 The purpose of the study reported here was to characterize the anatomic location and clinical signs of thymomas in goats and obtain long-term follow-up information on a subset of goats treated by tumor excision. We hypothesized that in goats, thymomas would be located in the ventral cervical region or mediastinum and that complete excision as the sole treatment would result in long-term (> 1 year) survival without the need for additional treatment.
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