Webster's New World Medical Dictionary

thyroid-stimulating immunoglobulin
A form
of immunoglobulin G (IgG) that can bind to thyroid
stimulating hormone (TSH) receptors on the thyroid
gland. Abbreviated TSI. TSIs mimic the action of
TSH, causing excess secretion of thyroxine and tri-
iodothyronine. The TSI level is abnormally high in
persons with hyperthyroidism due to Graves disease.
thyroidectomy
Surgery to remove part or all of
the thyroid gland. Thyroidectomy might be done to
remove a tumor or to treat hyperthyroidism or goi-
ter (enlarged thyroid gland). Complications of the
surgery can include vocal cord paralysis and acci-
dental removal of the parathyroid glands, which are
located behind the thyroid gland. Because the
parathyroid glands regulate calcium metabolism,
their removal can result in low calcium levels.
thyroiditis
Inflammation of the thyroid gland.
The inflamed thyroid gland can release an excess of
thyroid hormones into the bloodstream, resulting in
a temporary hyperthyroid state. When the thyroid
gland is depleted of thyroid hormones, the patient
commonly goes through a hypothyroid (low thy-
roid) phase. This phase can last for 3 to 6 months,
until the thyroid gland fully recovers. Thyroiditis can
be diagnosed with a thyroid scan or biopsy. For spe-
cific types of thyroiditis, please see their alphabeti-
cal listings.
thyrolingual cyst
See 
cyst, thyroglossal.
thyrotropin
See 
thyroid stimulating hormone.
thyroxine
A hormone that is made by the thyroid
gland and is one of the most important thyroid hor-
mones. Four iodine molecules are attached to the
molecular structure of thyroxine. Along with the
more powerful thyroid hormone triiodothyronine
(T3), thyroxine affects almost every process in the
body, including body temperature, growth, and
heart rate. Also known as T4.