Two thyroid lobes, one on either side of the trachea, make up the thyroid gland. Each lobe in a healthy cat is roughly 4-8 mm wide and 10-20 mm long. The thyroid lobes are closely related to the parathyroid glands, which have an exterior and an internal gland. A tiny percentage of cats may have ectopic tissue in their sublingual area or mediastinum.
The majority of cats have independent thyroid nodules that grow into adenomas on their own. Because they don’t respond to the typical feedback processes that are supposed to lower thyroid hormone production, these nodules are autonomous. Thyroid cancer affects about 2% of cats on average, however this rate rises over time in cats receiving treatment for hyperthyroidism. Over the past 40 years, the prevalence of hyperthyroidism in cats has steadily increased, although the underlying cause has not yet been identified. It has been hypothesised but not established that some factors including iodine-deficient diets or possible exposure to other substances such flavonoids, pesticides, phthalates, or others are to blame.