Thyroid Glossary

Below is a list of the most common terms associated with medical conditions of the thyroid gland.


This is a process to painlessly destroy the thyroid with radioactive iodine. For patients with Graves hyperthyroidism, a pill with a dose of 8 - 12 millicuries of I-131 is given by mouth which damges the thyroid over a 3-6 month period of time. This is the main way to treat North American patients with hyperthyroidism over the age of 30. Thyroid cancer treatment may require radioactive iodine and at much higher doses.

Anaplastic thyroid carcinoma:

A type of undifferentiated thyroid tumor which is very rare, very aggressive, and very difficult to treat. This tumor usually occurs in older patients with longstanding goiters and can suddenly produce compressive symptoms.

Antithyroid agents:

This is a class of medications, also called thionamides, include methamazole and propylthiouracil which inhibit iodide organification which can inhibit thyroid hormone production and peripheral thyroid effects.

Apoptosis / Apoptotic

A description of pre-programmed cell death that destroys a cell without damage to surrounding cells.

Autoimmune disease

A condition in which the bodies own antibodies attack itself. Thyroid autoantibodies can cause Graves disease or Hypothyroidism from Hashimoto's thyroiditis.

Beta adrenergic blocking agents:

These are drugs which inhibit the effects of excess thyroid hormone on the body by inhibiting the conversion of T4 to T3 at the tissue level. These medications will reduce heart rate and are also used an blood pressure lowering medications.


This is a 32 amino acid protein produced in the parafollicular C-cells of the thyroid gland that is involved in calcium and phosphate regulation. Medullary thyroid cancer is a tumor of these C-cells. Calcitonin can be used as a marker of medullary thyroid cancer disease progression.

Carcinogen embryonic agent (CEA):

In terms of thyroid disease, this is a blood marker that can be used to follow the disease progression of medullary thyroid cancer. This is a substance produced by many different cancers.


Abbreviation for computerized axial tomography "CT Scan"


These are the parafollicular cells derived from the ultimobranchial body which produce calcitonin, carcinoembryonic antigen (CEA), histaminase, prostaglandins, and serotonin. These cells are located in the thyroid gland and medullary thyroid cancer arises as a tumor of these cells.


In terms of thyroid disease, these are abnormal collection of fluid or blood within the thyroid gland. Complex cysts contain cystic and solid elements. Cysts are usually benign but complex cysts can contain cancer in the cyst wall. Thyroglossal duct cysts are specific form of thyroid cyst.


A description of the changes in the skin associated with Graves disease which consists of thickening of the skin, especially in the lower shin. Also known as pretibial myxedema. Occurs in 2% of patients with Graves and usually associated with opthalmopathy. This is best evaluated by a dermatologist.

Differentiated Thyroid Cancer:

These are thyroid cancers that arise from thyroid follicular cells, accounting for the majority of thyroid cancers. The common types of these cancers are: Papillary thyroid cancer- 85%, Follicular thyroid cancer- 10%, Hurthle cell or oxyphilic thyroid tumors- 3%. Generally, cancer stage for cancer stage, the prognosis of papillary thyroid cancer and follicular thyroid cancer are similar. Certain subtypes of papillary thyroid cancer which have microscopic vascular invasion and extension beyond the thyroid have a worse prognosis: tall cell variant, columnar cell variant, and diffuse sclerosing variant. This is in contrast the minimally invasive follicular thyroid cancer which is characterized histologically by microscopic penetration of the tumor capsule without vascular invasion and carries no excess mortality.

Compare Differentiated Thyroid cancer to Poorly Differentiated Thyroid Cancer.

Diffuse toxic goiter:

Hyperthyroidism due to Graves' disease. An autoimmune disease of unknown cause which causes thyrotoxicosis, goiter, opthalmopathy, and dermopathy (pretibial myxedema)


A physician with an internal medicine degree who has two to three extra years of specialized training in the endocrine hormone system. This system includes the thyroid gland, parathyroid glands, the pancreas, adrenal glands, and the pituitary gland.


Term to describe a state of being in normal thyroid balance when the TSH and the T4 levels are both within normal ranges.


This is the condition of protruded or bulging eyes which has multiple causes. One cause of this condition can be Graves thyroid eye disease.

Follicullar thyroid cancer:

This is the second most common tumor found in the thyroid. It tends to spread from the thyroid more often than papillary thyroid cancer.

Free T4:

This is a measure of the concentration of free thyroxine, the biologically active fraction of thyroxine. The free thyroxine is theoretically not affected by changes in concentrations of binding proteins such as TBG and thyroid binding prealbumin.


A latin word to describe a global enlargement of the thyroid gland


The type of hyperthyroidism caused by a globally overactive thyroid gland. Also known as diffuse toxic goiter or multinodular toxic goiter.

Hashimoto's Thyroiditis

This is a condition of thyroid autoantibodies that have the potential to reduce thyroid function over time.

Hashimoto's struma:

also referred to as Reidel's struma, chronic thyroiditis.

Hurthle Cells:

A large, eosinophilic cell derived from thyroid follicular epithelium by accumulation of mitochondria which causes these cells to look larger than usual follicular cells.

Hurthle Cell Carcinoma:

Four percent of thyroid tumors are caused by excess hurthle cells which can be either benign or malignant. A pathologist can differentiate benign versus malignant by whether there is spread into the capsule or blood vessels.


The term used to refer to any condition in which the thyroid gland itself is overproducing too much thyroid hormone. This is a subset of the term thyrotoxicosis.


A condition in which the parathyroid glands are overproducing parathyroid hormone. There are three different types: primary, secondary, and tertiary. Depending on the degree and duration of this elevation in parathyroid hormone, the patient may have no symptoms, osteitis fibrosa cystica, elevated serum calcium, decreased serum phosphorus, and increased excretion of both calcium and phosphorus.


A condition due to an increase in the secretion of parathyroid hormone is decreased. This condition usually leads to hypocalcemia.


A condition in which the amount of effective thyroid hormones in the body is below normal. This is the most common form of thyroid function abnormality. Symptoms include fatigue, slowness, depression, and feeling cold


Two of these protein residues in the thyroglobulin protein are combined with inorganic iodine in the organification process to form thyroxine and tri-iodothyronine.


This is the generic name for the seven different formulations of synthetic T4 thyroid hormone. This medication has 12 successively pill strengths. The differences between successive pill strengths within a particular levothyroxine formulation is 10-12%. There seven different formulations are considered equivalent by the FDA, but when interchanged, are allowed to up to 10% different from each other. The American Thyroid Association recommends to avoid switching brands during therapy therapy due to this variability in formulations.


drug; different brands of the thyroid hormone T4 or levo-thyroxine.


Surgical removal of one of the thyroid lobes.

Lymph node:

Oval shaped masses of tissue scattered throughout the body which act as filters to help fight infections. When thyroid cancers spread to other parts of the body via these nodes they can become abnormally and persistently enlarged.

Medullary thyroid carcinoma:

A thyroid cancer that may occur as a sporadic form or as a genetically transmitted familial form. Pathologically there is a proliferation of parafollicular cells ("C" cells) that produce excessive calcitonin, Many cases are now diagnosed during routine screening of affected family members with multiple endocrine neoplasia (MEN) types II or IIa before a tumor develops.


The spread of thyroid cancer from the thyroid gland to another part of the body. This usually results from dissemination of tumor cells by the lymphatics or blood vessels, or by direct extension

Multiple Endocrine Neoplasia

Distinct genetic syndromes which cause tumors of endocrine glands. There are three known syndromes of MEN including MEN1, MEN2a, MEN2b.


A small node or overgrowth of tissue. This is a common condition affecting thyroid tissue.


These are changes in the eyes that are one of the physical signs associated with Graves disease. The extent of the involvement of the eyes is classified by the Werner classification system.


This is the description of the process by which the thyroid gland couples together inorganic iodide and the main thyroid protein thyroglobulin.


Fast and forcible pulsations of the heart that can be associated with thyroxicosis.

Papillary thyroid cancer:

The most common type of thyroid malignancy. Under microscope there appears to be multiple projections with a fern-like appearance.


Glands in the body that are located next to the thyroid gland in the neck. There are usually four of these glands. They control the secretion of parathyroid hormone which controls blood calcium balance.

PET scan:

Positron Emission Tomography; identifies differences in how quickly cells metabolize glucose. Cancer cells generally metabolize glucose more quickly than normal cells but a positive scan does not necessarily diagnose cancer.

Poorly Differentiated Thyroid Cancer

These are aggressive tumors of the thyroid which are more difficult to treat because they no longer have many characteristics of true thyroid cells. The tumor histologies include trabecular, insular, and solid subtypes of papillary thyroid cancer. Also see anaplastic thyroid cancer. Compare to Differentiated Thyroid Cancer.

Postpartum thyroiditis:

An inflammation of the thyroid gland which may occur in the mother's thyroid gland after the birth of a child. This can sometimes lead to permanent hypothyroidism in the mother.

Pretibial myxedema:

See dermopathy.


Abbreviation for Radioactive Iodine.

Radioactive iodine:

A medication used for two purposes. In small quantities is can diagnose different forms of hyperthyroidism. In larger amounts is can treat hyperthyroidism or thyroid cancer. The medication is usually administered in the form of a capsule or liquid (it is odorless and tasteless). Since the thyroid is the major organ in the body that uses iodine, the radioactive iodine is quickly take up by the overactive thyroid cells. Over a 6 month period of time this results in the destruction of the thyroid gland.

Resin T3 uptake:

The blood test is used to assess the binding capacity of the serum for thyroid hormone. In conjunction with the total T4, the Free T4 index can be calculated which reflecting the free T4 level. This testing is frequently used to follow hyperthyroidism in pregnancy.

RET proto-oncogene:

This is a gene in the body, which is abnormal, is strongly associated with medullary thyroid cancer. Activating mutations in the RET gene can give rise to the cancer syndrome multiple endocrine neoplasia (MEN). The gene can be evaluated in a blood test to determine if the Medullary Thyroid Cancer is sporadic or familial (hereditary)


A brand name of the of the synthetic thyroid hormone T4 or (levothyroxine)


This is a large protein produced within the thyroid gland which is stored in the colloid of the thyroid follicular cells. This protein allows the thyroid to combine inorganic iodide with iodotyrosine molecules to form the main thyroid hormone, thyroxine.

Thyroglossal duct cyst:

This is a remnant of the thyroglossal duct tract. The thyroid originally develops at the base of the tongue and then moves along the thyroglossal duct tract tract to its final location in the neck during embryogenesis. This thyroglossal duct tract should atrophy and disappear by the 10th week of gestation but in some people remnants of this tract remain into adulthood. There is a 1% risk of either follicular or papillary thyroid cancer in these cysts.


This a hormone producing gland located in the neck which produces thyroid hormone. There are two types of abnormalities that can occur in this gland: 1) functional thyroid problems (hyperthyroidism or hypothyroidism) which are monitored with blood testing and 2) structural thyroid problems (thyroid nodules, goiter, thyroid cancers) which are monitored using thyroid ultrasound.


An inflammation of the thyroid gland. Hashimoto's thyroiditis is the most common cause of hypothyroidism.

Thyroid Cancer:

There are many forms of thyroid carcinoma.

Thyroid Nodules:

These are growths of thyroid tissue on the thyroid gland.

TNM Thyroid Cancer Staging:

A staging system is a standard way for your endocrinologist to summarize how large a cancer is and how far it has spread. The most common system used for thyroid cancer is the TNM system. "T" indicates the size of the primary tumor and whether it has grown into a nearby structure. "N" describes the extent of spread to nearby lymph nodes. "M" indicates whether a cancer has spread (metastasized) to other organs of the body. The most common sites of spread for thyroid cancer are the lungs, then bones and liver. Survival rates can be based on this staging system.

Papillary thyroid cancer*

*based on patients diagnosed 1998 to 1999

Follicular thyroid cancer*

*based on patients diagnosed 1998 to 1999

Note: All the stage III and IV patients with follicular or papillary thyroid cancer are, by definition, over 45 years old.

Medullary thyroid cancer**

**based on patients diagnosed between 1985 and 1991


The 5-year relative survival rate for anaplastic (undifferentiated) carcinomas, all of which are considered stage IV, is around 7% (based on patients diagnosed between 1985 and 1991).

Thyroid storm:

This is a severe form of untreated thyrotoxicosis which causes multiple organs to fail. The death rate in these patients is very high.


The surgical removal of part or all of the thyroid gland.


The presence of excess thyroid hormone in the body which can be due to intrinsic excess (hyperthyroidism) or extrinsic excess hormone (ingesting thyroid hormone)


The hormone produced by the thyroid gland.


See Triiodothironine or Cytomel.


see Thyroxine.

Total T3:

The total T3 measures the concentration of triiodothyonine in the serum.

Total T4:

The T4 test measures the concentration of Thyroxine in the serum. This includes both bound and free hormone. Only the free hormone, about 0.05% of the total, is biologically active.

TRH test:

An antiquated form of testing for thyroid hormone deficiency.


Thyroid Stimulating Hormone is secreted from the pituitary gland to stimulate the thyroid gland to produce thyroid homones. This is the most sensitive test to evaluate for thyroid excess or deficiency.

Werner classification system:

A system (Class 1 though 6) used to classify the severity of opthalmopathy (eye changes) in Graves disease.