Contributions to the Investigation of Thyroid Enlargement in the Horse

Twelve horses with unilateral thyroid enlargement, were investigated during a one year period. This study was set up to try to relate thyroid enlargement to thyroid function in the horse. General clinical examination, ultrasound scanning, TSH stimulation test, serum T4 determination, scintigraphy and histopathological study of the gland was carried out. Two follicular adenocarcinomas, 1 suspected adenoma of the parafollicular (C. ) cells, accompanied by thyroid follicular hyperplasia and 4 follicular adenomas and one hyperplastic goitre were diagnosed. All of them were euthyroid (normal thyroid hormone base levels), and primary dysfunction of the gland could not be detected, indicating that, in our cases unilateral thyroid enlargement did not alter thyroid function