Abstract Ectopic thyroid tissue can be found in adult dogs at the base of the tongue, the cardiac base, the mediastinum and the ventral cervical region, and it is rarely associated with the development of neoplasia. This report aims to present a case of ectopic thyroid carcinoma at the cardiac base in a 12‐year‐old male Yorkshire terrier with a previous diagnosis of granulomatous meningoencephalitis. Postmortem examination revealed a mass in the mediastinum that adhered to the visceral pleura. The microscopic examination revealed epithelial cells forming tubules with strongly eosinophilic material in the lumen (colloid) and epithelial nests. Immunohistochemical staining for thyroid transcription factor‐1 was detected in 40% of the cells. Brain lesions consistent with granulomatous meningoencephalitis were found, and a neoplastic embolus was observed in a blood vessel in the pia mater.
Matos et al. (Fri,) studied this question.