Glossary

First Letter: A-H | I-R | S-Z

Amino acid sequence - The unique order of the "building blocks" (amino acids) that make up each protein.

Anaplastic thyroid cancer - Undifferentiated, fast-growing thyroid cancer.

Anovulation - The absence of ovulation, or egg production, in a woman’s reproductive cycle.

Antithyroid agents - Drugs that block the production of thyroid hormones by the thyroid gland.

Antithyroid antibodies - Antibodies that act against the tissue in the thyroid gland; also called antithyroid autoantibodies.

Asthenia - Weakness.

Basal metabolic rate (BMR) - The rate of metabolism, or how fast the body uses calories and oxygen to produce energy.

Benign - A word to describe a non-malignant growth or mild illness.

Biopsy - Removing tissue from patients for examination.

bTSH - Bovine (cow) thyroid-stimulating hormone.

CAT scan - Computerised axial tomographic scan; an imaging procedure. Also called CT scan. Computed tomography is useful for evaluation and follow-up of thyroid cancer patients and for assessing the extent of metastatic and vascular invasion. It is not useful in differentiating benign from malignant thyroid nodules.

Clearance - The rate at which a substance is removed from the blood through normal processes.

Cold nodule - A lump in the thyroid gland that does not take up iodine on a scan as well as the surrounding thyroid tissue does.

Computerised rectilinear thyroid (CRT) scanner - The preferred instrument used today for thyroid scanning.

Controlled clinical trials - Studies in which results observed in patients receiving a drug are compared to the results in patients who did not receive the drug.

Count - A unit of measurement (used to gauge levels of radioactivity).

CT scan - Computerised axial tomographic scan; an imaging procedure. Also called CAT scan. Computed tomography is useful for evaluation and follow-up of thyroid cancer patients and for assessing the extent of metastatic and vascular invasion. It is not useful in differentiating benign from malign thyroid nodules.

Diffuse goitre - An enlargement of the entire thyroid gland.

Endocrine glands - Glands that secrete hormones into the bloodstream.

Endocrinologists - Doctors who specialise in the care of patients with disorders of the endocrine glands.

Endocrinology - The study of diseases and disorders of the endocrine system (like thyroid diseases and diabetes). The endocrine system consists of glands in the body that release hormones directly into the blood. The thyroid gland, for example, releases thyroid hormones into the bloodstream, giving the hormones access to all other cells of the body. The purpose of the secreted hormones is to evoke a specific response in other faraway cells.

Euthyroidism - Having the proper amount of thyroid hormone in the body.

Fine needle aspiration biopsy (FNAB) - A biopsy obtained by inserting a thin needle into a thyroid nodule and extracting cells for analysis. Also called fine needle aspiration (FNA).

Follicles - Microscopic spherical units that make up the thyroid gland.

Follicular cancer - A type of cancerous growth composed of thyroid follicular cells; also called follicular carcinoma. Follicular cancer is a type of well-differentiated thyroid cancer.

Free T4 - The amount of T4 in the bloodstream that is not bound to carrier proteins.

Free thyroxine index (FTI or T7) - A calculation using T4 resin uptake and total T4 to estimate free T4 in the bloodstream.

Gamma camera - Stationary instrument that produces images of the thyroid gland after oral administration of radioactive materials.

Goitre - An enlargement of the thyroid gland for any reason. It may be a generalised enlargement (diffuse) or asymmetric (nodular).

Hormones - Chemicals produced by an endocrine gland and released into the blood. Hormones travel to other organs of the body where they produce their effect.

Hot nodule - A lump in the thyroid gland that takes up more radioactive iodine on a scan than the normal surrounding thyroid tissue does. Hot nodules are rarely cancerous.

hTSH - Human thyroid-stimulating hormone.

Hürthle cell cancer - A form of follicular thyroid cancer. Pronounced her’ tuhl cell.

Hyperthyroidism - An abnormality of the thyroid gland in which secretion of thyroid hormone is usually increased and no longer under normal control. Characterised by increased metabolism.

Hypothalamic-pituitary-thyroid axis - A negative feedback mechanism through which hormone secretion is regulated. The hypothalamus secretes a releasing hormone (TRH) that stimulates the pituitary to secrete thyroid-stimulating hormones, which then enter the circulation.

Hypothalamus - An endocrine gland in the brain that releases thyrotropin-releasing hormone (TRH).

Hypothyroidism - decreased production of thyroid hormone, leading to symptoms of thyroid insufficiency.

Isthmus - A small piece of thyroid tissue that connects the right and left lobes of the thyroid gland.

Larynx - The upper part of the trachea that contains the vocal cords, sometimes called the voice box.

Levothyroxine sodium - Thyroid hormone supplements.

Lobectomy - Surgical removal of all or part of one lobe of the thyroid. Indicated in some cases of thyroid cancer.

Lobes - The two halves of the thyroid gland that give it its butterfly-like shape. The right lobe is often slightly larger than the left lobe.

Lyophilisation - Freeze drying.

Magnetic resonance imaging (MRI) - An imaging procedure that produces a clear three-dimensional picture.

Medullary thyroid cancer - Thyroid cancer arising from the parafollicular cells. Although it grows slowly, it may be harder to control than papillary and follicular tumours. It is more aggressive than well-differentiated thyroid cancer and tends to spread to other parts of the body.

Metabolism - The use of calories and oxygen to produce energy.

Metastatic disease - Cancer that has spread from its original site to other parts of the body.

Mortality rate - Death rate.

MRI - Magnetic resonance imaging; an imaging procedure that produces a clear three-dimensional picture.

Multi-nodular goitre - A goitre in which the enlargement consists of multiple lumps.

Open-label trial - A clinical trial in which doctors and participants know which treatment is being administered to which patients.

Papillary cancer - A well-differentiated thyroid cancer composed of thyroid follicular cells. Also called papillary carcinoma. The nuclei of the cells are large and seem to overlap.

Parathyroid glands - Four glands located on the back of the thyroid that produce parathyroid hormone.

Paresthesia - Burning, prickling, or tingling sensation in the skin.

PET (positron emission tomography) scan - An imaging technique that uses radioactive positrons (positively charged particles) to detect subtle changes in the body's metabolism and chemical activities.

Pituitary gland - A small gland the size of a peanut that is located behind the eyes at the base of the brain. It secretes hormones that control other glands (including the thyroid) as well as growth. It secretes thyroid stimulating hormone (TSH), a hormone that helps control thyroid function, as well as other hormones involved in endocrine function.

Prognostic indicators - Factors that can help predict a likely outcome (as in how, on average, thyroid cancer will progress).

Quality of life (QOL) - A person’s physical, mental, and social well-being. Also known as health-related quality of life (HRQOL).

Radioactive iodine (RAI) - Radioactive isotopes of iodine (131I or 123I) used in the diagnosis and treatment of some thyroid disorders. RAI is also used for treatment of thyroid cancer, in which cases the patient takes a large dose of radioactive iodine to kill any recurrent or metastasised thyroid cells.

Radioactive iodine uptake (RAIU) - A test measuring the amount of orally administered radioactive iodine taken up by the thyroid gland.

Radioactive isotopes - Unstable chemical elements that are used in diagnostic testing for thyroid disorders including thyroid cancer.

RAI ablation - Administration of a radioactive form of iodine (131I) to try to destroy any remnant (normal or cancerous) thyroid tissue left after surgery in the thyroid bed or neck.

Recombinant DNA technology - The technique of isolating genes from one organism and purifying and reproducing them in another organism; sometimes called genetic engineering.

Recombinant human thyroid-stimulating hormone (rhTSH) - A large protein molecule almost identical to human thyroid-stimulating hormone that has been produced using recombinant DNA technology.

Sensitivity - The ability of a test to detect the proportion of true positive results for the disease that the test is intended to reveal. In other words, the probability that, given the presence of disease, a test result indicates the presence of disease.

Signs - Those characteristics that a physician can objectively detect or measure. If the physician touches the patient's skin and notes that it is warm and moist, this is a sign. (See symptoms.)

Specificity - The ability of a test to detect the proportion of true negative results for the disease that the test is intended to reveal. In other words, the probability that, given the absence of disease, a test result excludes disease.

Standardised - Using different techniques or preparations in order to conform to a reference or standard.

Statistics - The study of probabilities. Statistics are used in clinical trials to determine whether results obtained with the study drug are truly different from those obtained with the control (or placebo).

Symptoms - Those problems that a patient notices or feels. If a patient feels hot, this is a symptom. (See signs.)

T3 (triiodothyronine) - The secondary hormone produced by the thyroid gland.

T4 (thyroxine) - The primary hormone produced by the thyroid gland.

Tg test - A test that measures the level of thyroglobulin (Tg) in the blood. Tg tests are used in the postsurgical monitoring of thyroid cancer patients to check for thyroid remnants or cancer metastases.

THT (thyroid hormone therapy) - Therapy consisting of thyroid hormone medications.

Thyroglobulin (Tg) - A large protein that acts as a storage site for thyroid hormones within the thyroid gland. Following surgical removal of a cancerous thyroid gland, the level of Tg in the bloodstream can be monitored to detect thyroid cancer recurrence.

Thyroid bed - The area of the thyroid that remains after surgical removal of the thyroid gland.

Thyroid-binding proteins - Proteins to which thyroid hormones attach themselves and thus circulate in the bloodstream.

Thyroid gland - A two-lobed gland lying at the base of the throat that produces hormones essential for a variety of metabolic processes in the body. When iodine is ingested, much of it goes to the thyroid gland.

Thyroid hormone suppression therapy (THST) - In patients who have had a thyroidectomy for thyroid cancer, physicians usually prescribe a moderate excess of thyroid hormones to create a negative feedback loop that suppresses thyroid-stimulating hormone production by the pituitary gland. TSH production is suppressed to avoid stimulating existing thyroid remnants or thyroid cancer cells.

Thyroid hormones - T4 and T3, two hormones that tell the body how fast to work and how to use energy. T4 (thyroxine) is the primary hormone produced by the thyroid gland and T3 (triiodothyronine) is the secondary hormone produced by the thyroid gland.

Thyroid nodules - Small lumps or growths that can be felt in the neck. They can be benign or malignant. In a normal gland or a multinodular goitre, thyroid nodules may be solitary or multiple. Imaging tests, blood tests, and fine needle aspiration biopsies (FNAB) are used to perform a clinical evaluation of thyroid nodules.

Thyroid remnant - Some part of the original thyroid gland remaining after thyroidectomy surgery.

Thyroid scan - A picture of the thyroid gland obtained with a rectilinear scanner and radioactive materials.

Thyroid-stimulating hormone (TSH ) - A hormone secreted by the pituitary gland that stimulates the thyroid gland to produce the thyroid hormones T4 and T3. When the thyroid gland is not working properly, the pituitary releases large amounts of TSH to try to stimulate the thyroid gland into producing thyroid hormone. High amounts of TSH circulating in the bloodstream thus indicate that the thyroid is not secreting enough hormones.

Thyroid ultrasound - A type of scan that uses sound waves that pass into the body and reflect back to produce images.

Thyroidectomy - Surgical removal of the thyroid gland.

Thyroiditis - Inflammation of the thyroid gland.

Thyroidologists - Doctors who specialise in the treatment of diseases of the thyroid.

Thyrotropin receptor - The matching site on a thyroid cell that selectively captures thyroid stimulating hormone (TSH) to stimulate the production of thyroid hormones by the thyroid gland.

Thyrotropin - Another name for thyroid-stimulating hormone (TSH).

Thyrotropin-releasing hormone (TRH) - A hormone released by the hypothalamus that stimulates the pituitary gland to secrete thyroid-stimulating hormone (TSH). Also called thyroliberin.

Thyroxine (T4) - The primary hormone produced by the thyroid gland. T4 contains four atoms of iodine.

TNM - A tumour staging system for classifying patients with thyroid cancer into groups based on tumour size (T), presence of lymph node metastases (N), and the presence of distant metastases (M). Also referred as "tumour-node-metastasis."

Toxic multinodular goitre (TMNG) - A thyroid gland that has multiple nodules functioning independently of the usual control mechanisms. They can cause the thyroid to produces too much thyroid hormone and cause hyperthyroidism.

Trachea - The windpipe.

Triiodothyronine (T3) - The secondary hormone produced by the thyroid gland. It contains three atoms of iodine and is the metabolically active thyroid hormone.

TSH test - A test to measure the amount of thyroid-stimulating hormone (TSH) in the bloodstream.

Ultrasound - An imaging technique used to obtain pictures by bouncing sound waves off an object.

Undifferentiated thyroid cancer - A form of thyroid cancer in which the cancer cells do not resemble thyroid cells. See anaplastic thyroid cancer.

Well-differentiated thyroid cancers - Papillary or follicular thyroid cancers showing well-differentiated cell structures.

Whole body scan (WBS) - A scan of the whole body used to view areas of radioactive iodine uptake after its oral administration.

Withdrawal scan - A radioactive iodine (131I) whole body scan performed when the patient has been withdrawn from thyroid hormone suppression therapy long enough for thyroid-stimulating hormone (TSH) levels to rise.