The thyroid is a small butterfly-shaped gland at the base of your throat. Though small, it's job is huge: to regulate and manufacture hormones that control growth and metabolism. Sometimes, an abnormal growth may appear on the thyroid. A doctor may discover it by feeling it with her hands or a person might see it when looking in the mirror. Chances are, this growth is a cyst. According to the Mayo Clinic, about half of all people have a thyroid cyst (also called a "thyroid nodule"), though many people never know it is there.
What is a thyroid cyst?
A thyroid cyst is a fluid-filled sac that has grown on the thyroid. The cyst may be very small (less than 1mm in diameter) or so large that it may be visible to the naked eye, appearing as a lump on your throat. Some cysts are entirely filled with fluid ("cystic") and others are composed of both fluids and solids ("complex"). If the cyst is large and complex, a doctor may want to biopsy its components to make sure that it is not cancerous.
Symptoms of a Small Cyst
People with smaller cysts (3mm or smaller) on their thyroid typically don't have any symptoms. Most of these people will not realise that they have a cyst until a doctor discovers it during an exam.
Symptoms of a Large Cysts
People with larger cysts do not necessarily have any symptoms either, although they may feel or see a lump at the base of their throat. However, sometimes those with large cysts may feel it pressing against their windpipe, have pains in their neck, have trouble swallowing, or less frequently, have a change in the tone and quality of their voice as it presses against their vocal cords. Cysts are rarely cancerous, but malignant cysts tend to feel hard, grow large quickly, and cause a change in your voice more often than benign cysts. Occasionally large cysts can affect the function of your thyroid and cause you to overproduce or underproduce the hormone that stimulates the thyroid (thus causing a hyperactive or underactive thyroid).
No one knows for certain what causes thyroid cysts to develop, however, it is believed that the following factors may have some relation: a lack of iodine in the diet, an autoimmune disorder that causes inflammation of the thyroid (Hashimoto's disease), a genetic defect, exposure to radiation in childhood. Further, you are more likely to develop a thyroid cyst if you are: a woman, over the age of 40, or if one of your parents or siblings has a thyroid cyst.
If your cyst is large, fast-growing, complex or otherwise "suspicious" your doctor may want to do a fine-needle aspiration (FNA) biopsy to make sure that it is not cancerous. In this 20-minute procedure, your doctor will insert a very thin needle into the nodule and withdraw a sample of its components. The sample will be analysed at a laboratory. If the components are determined to be malignant or suspicious, you'd likely need to have surgery to remove the cyst and determine the extent of the malignancy. Your doctor can also evaluate the nodule through an ultrasound or blood tests to determine whether and/or the extent to which it is affecting the function of your thyroid. These methods do not, however, determine whether or not the cyst is malignant.
Usually there is no treatment required for cysts, particularly if the cyst is small and fluid-filled. Your doctor may want you to come in for follow-up visits, however, to monitor the growth and nature of the cyst, plus take periodic blood test to make sure the cyst is not affecting the functioning of your thyroid. Alternatively, you might be placed on thyroid hormone suppression therapy to shrink the cyst (although many doctors find this unnecessary, if the cyst is small and determined to be non-malignant). If the cyst is affecting the functioning of your thyroid, you may be required to take radioactive iodine for a few months. The iodine can help shrink the nodules.