Thyroid Overview

The thyroid is a butterfly-shaped gland which lies low in the front of your neck, near the windpipe (trachea). It consists of two halves (lobes), each about the size of a cherry tomato, connected by a small bridge of tissue (isthmus). The thyroid produces two important hormones called thyroxine (T4) and a smaller amount of triiodothyronine (T3). Thyroid hormones are essential for growth, development, and metabolism. They are also involved in the optimal functioning of essential organs in your body, such as the heart and brain.

The amount of T4 and T3 hormone that is produced in your body is controlled by another hormone: Thyroid Stimulating Hormone (TSH). A simple blood test can measure the level of T4 and TSH you have in your body and allows doctors like Dr. Hall to determine whether your thyroid is functioning properly or not.  

Iodine in the blood stream is actively taken up by thyroid cells through an area on the cell surface called a symport. This uptake of iodine is controlled by TSH. Once inside the thyroid cell, iodine undergoes several chemical processes and is combined with thyroglobulin (a protein made in the thyroid gland) to make thyroid hormones. The thyroid hormones are released under the control of TSH.

T3 is more biologically active than T4. T4 is converted to T3 mainly in the liver and kidneys by an enzyme called type 1 deiodinase. T4 is also converted to T3 in the brain and muscles by an enzyme called type 2 deiodinase. Gut bacteria also convert T4 to T3.  

A goitre is a medical term for an enlarged thyroid. A multinodular goitre is an enlarged thyroid with lots of nodules (lumps) in the thyroid. The thyroid may be enlarged due to benign (non-cancerous) thyroid enlargement, thyroid cancer, or inflammation of the thyroid. Worldwide, the most common cause of a goitre is iodine deficiency, but this is not the case in New Zealand.

Goitres are more common in women, diabetics and smokers. Goitres also tend to run in families. The autoimmune conditions called Graves’ disease and Hashimoto’s thyroiditis can both cause a goitre. Cassava, soya beans, selenium deficiency, nitrates and polychlorinated biphenyls are all associated with goitres.

Goitres and Symptoms

Many goitres cause no symptoms. However, the larger a goitre is, the more likely it is to cause symptoms. Symptoms include:

• A mass or lump in the neck.
• A pressure feeling (globus sensation) in the neck.
• Difficulty swallowing.
• Shortness of breath, especially on minimal exertion (walking up a single flight of stairs) or when lying down. This is due to compression (squashing) of the trachea (windpipe). Some people need to sleep with several pillows or in a recliner chair so they can breathe more easily.
• Feeling lightheaded (or going red in the face) when hanging out the washing.

Testing for a Goitre

All patients with an enlarged thyroid gland need a thyroid blood test and an ultrasound scan. Thyroid tests (fT4 and TSH) are usually but not always normal in patients with a goitre. If the goitre is very large or if you are having trouble breathing, you will also need a CT scan to determine the full extent of the goitre.

A goitre that is heading down under the sternum (breastbone) is called a retrosternal goitre and a CT scan is needed to determine the size of the goitre and the degree of tracheal compression (how much the goitre is squashing the wind pipe). A CT scan also helps with surgical planning.

If you have a goitre but have no symptoms and your thyroid blood test is normal, then you do not have to undergo surgery.

Surgery (thyroidectomy) is recommended if:

1. You have significant symptoms (see above)
2. You are hyperthyroid (low TSH and high fT4 or low TSH and normal fT4). First you will need to take carbimazole to control the hyperthyroidism. Once this is under control surgery can proceed.
3. If there are concerns that there is cancer in any thyroid nodules. This is determined with ultrasound, an ultrasound guided FNA, and in some cases molecular studies. Note there is little point doing an FNA if you are going to have surgery anyway.

Surgery involves either removing half of your thyroid (hemithyroidectomy) if only half of your thyroid is enlarged, or more commonly removing all of your thyroid (total thyroidectomy) if both sides of your thyroid are enlarged. – See thyroidectomy section of the site.