Roth DR, Perentes E.
Microscopic examination of the heart of a clinically normal 14-month-old female Beagle dog revealed the presence of ectopic thyroid tissue at the base of the heart, around the aorta, and intracardially at the level of the left ventricle and the aortic valve. The tissue was composed of well-differentiated follicles lined by a cuboidal epithelium and containing colloid. Follicular cells and colloid exhibited strong thyroglobulin immunoreactivity, while no parafollicular cells were noted and the immunoreactions for calcitonin remained consistently negative. Although in the dog ectopic thyroid tumors represent 1-10% of all heart base neoplasms (Capen, 1978; Bracha et al., 2009), to the best of our knowledge, nonneoplastic ectopic thyroid tissue has not been reported in the heart of the dog itself or within the dog aortic valve.