Thyroid gland — Since thyroid disease is a fairly common hormone disorder in older cats, every cat's thyroid will be palpated which may detect an abnormal enlargement of the thyroid gland in the neck. (vetforcatsonly.com)
Over-activity can be caused by enlargement of the thyroid glands or by a non cancerous tumor. (best-cat-art.com)
Peterson ME: The Thyroid Gland (Hypothyroidism, Non-neoplastic Enlargement of the thyroid gland, and Hyperthyroidism, In: Fraser CM (ed), The Merck Veterinary Manual, 7th Ed, pp 279 - 285, 1991 (animalendocrine.com)