About Thyroid

About the Thyroid Gland

Anatomy

The thyroid is an endocrine gland located in the front of the neck just below the ‘Adam’s apple’. It consists of two lobes that are positioned on both sides of the windpipe.  These lobes are joined in the middle by a bridge of thyroid tissue called the isthmus.  The thyroid is frequently compared to butterfly because of its shape but it can be compared to a bowtie, which is worn exactly where thyroid is, in front of the lower neck. The size of the thyroid varies and depends on age and body mass but is also related to amount of iodine in any geographical area. The average size is 5 x 3 x 2 cm and weight 20 – 25g but in the areas of high iodine intake (Iceland) it could be smaller (10 – 12g) when in countries with low iodine intake (Switzerland) it could be bigger (around 50g).

Physiology

The thyroid gland produces hormones called thyroxine (T4) and triiodothyronine (T3). These hormones stimulate the growth of the developing child and increase the metabolic rate of the body (the rate at which energy is consumed). Thyroid disease can result in either under active (hypothyroidism) or overactive (hyperthyroidism) gland.

The thyroid is controlled by the pituitary, part of the brain, which secretes thyroid stimulating hormone (TSH) that stimulates the thyroid gland to secrete T3 and T4.

T3, T4 and TSH can be measured in the blood and give us a very accurate picture of whether the gland is over or under active.  These tests are called ‘thyroid function tests’

Calcitonin is another thyroid hormone produced by C cells. Together with parathyroid hormone it regulates blood calcium levels.

Frequently asked questions

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Thyrotoxicosis, also known as hyperthyroidism is an overactive thyroid and is caused by excessive production and release of thyroid hormones. Most commonly it is caused by an autoimmune disease called Grave’s disease, when the antibodies produced by the immune system stimulate production of thyroid hormones. Other causes of hyperthyroidism are toxic multinodular goitre or solitary adenoma. It can also happen when a patient takes too many Thyroxine tablets.

Typical symptoms of hyperthyroidism are weight loss despite an increased appetite, intolerance of heat, tremor of the hands, anxiety, palpitations, excessive sweating and decreased need for sleep.  Cancer of the thyroid does not usually cause changes in activity of the thyroid.

Thyrotoxicosis can be treated with antithyroid drugs, radioiodine or surgery.

Most patients with thyrotoxicosis will at first be treated with antithyroid drugs such as Carbimazole or Propylthiouracil to control the thyroid overactivity. These drugs decrease the production of T3 and T4. Medications may be continued for up to 18 months but after withdrawal of treatment a significant number of patients will experience recurrence of the problem. Antithyroid drugs can cause side effects, such as low blood count or skin rash, which may require them to be stopped. Patients who relapse or have developed side effects will need a more permanent treatment using radioactive iodine or surgery.

Yes, it requires swallowing a capsule containing radioactive iodine, which is taken up by the thyroid gland and destroys the thyroid cells that are causing the overactivity.  Patients with small thyroids are successfully treated with only one course of treatment but large goitres require more than one.  The major side effects of this treatment are that you have to stay away from other people, particularly pregnant women and young children for several days until the level of radioactivity drops. 

Radioactive iodine therapy is not recommended for young women who are or wish to become pregnant, children and patients with significant eye disease. There is no evidence of long term harm from taking radioactive iodine although most patients who take it will develop an under active thyroid sooner or later and require to take thyroid tablets.

 

Surgery is a suitable option for many patients with an overactive thyroid gland when antithyroid drugs do not work and radioactive iodine is not recommended. 

Near total thyroidectomy (removal of almost all thyroid) is the operation recommended for treating Graves disease. This has the great advantage of solving the problem once and for all with no risk of recurrence of the overactivity and no requirement for frequent monitoring, provided that the thyroid tablets are taken for the rest of your life. Subtotal thyroidectomy (removal of 3/4 of the gland) is not recommended as the recurrence rate of thyrotoxicosis is high.

When a decision has been made to proceed with surgery it is important that the effects of thyroid over activity are controlled beforehand.  This requires you to take the prescribed medication up to the time of the operation.  If you have been prescribed a beta blocker (eg. propranolol) you must continue to take these for a few days after the operation.  Your doctor will advise you if this is necessary.

Hypothyroidism can be the result of dietary iodine deficiency but most commonly in adults is caused by an auto-immune disease called Hashimoto’s thyroiditis, an auto-immune disease is the body’s immune system reacting against its own tissue. Auto-immune disease of the thyroid can be detected by measuring antibodies in the blood.

Hypothyroidism of infancy results in irreversible mental retardation.  Hypothyroidism in adults causes mental and physical slowness, lethargy, memory loss, hoarse voice, increased weight and intolerance of cold.  The skin becomes dry and the eyes may be swollen.  Constipation is common. Hypothyroidism can be very successfully treated with thyroxine tablets.

The normal thyroid has considerable spare capacity for making thyroxine therefore after the removal of as much as half of the gland there might be no need for taking thyroxine.  However, if the whole thyroid has been removed you will need to take thyroxine daily for the rest of your life. 

Blood tests are an important part of assessment and include Thyroid Function Test (T3, T4, TSH), calcium, parathormone, vitamin D, thyroid antibodies, calcitonin and thyroglobulin levels. Other routine blood tests might also be requested.

Ultrasound is the best initial assessment of the size, number and density of thyroid nodules and lymph nodes as well as their relation to other anatomical structures. Other scans such as chest X ray, CT, PET, MRI or radioactive iodine scan might be necessary.

Biopsies of the thyroid are performed with a small needle under local anaesthetic and help to establish an accurate diagnosis. This is the best way to differentiate between cancer and benign thyroid nodules.

Voice box assessment (laryngoscopy) is performed before surgery if change in voice (hoarseness) has occurred or repeated surgery is required.

Commonest indications for thyroid surgery are:

  • Large thyroid (goitre) especially if it is extending into the chest and causing pressure symptoms such as difficulty swallowing or breathing (stridor)
  • Presence of thyroid nodule if clinical features or biopsy suggestive of cancer
  • Overactive thyroid (hyperthyroidism).
  • Cosmetic (patient’s choice)

A goitre is an enlargement of the thyroid gland.  The commonest cause of a goitre worldwide is iodine deficiency. Retrosternal goitre is diagnosed when thyroid enlargement extends from the neck into upper chest.

Large and retrosternal goitres can compress gullet or windpipe and cause difficulty in swallowing (dysphagia) or difficulty in breathing (stridor).  They can also compress veins and cause facial congestion. Dysphagia, stridor and venous congestion are known as pressure symptoms.

Even large goitres which are not cancers rarely cause a change in voice.

A cancer of the thyroid is a rare tumour and represents probably 1% of all the cancers. There are less than 1,000 new cases of thyroid cancer a year diagnosed in the United Kingdom.

It is usually a slowly growing tumour that can be successfully treated and cured.  The commonest thyroid cancer is a papillary cell carcinoma, which affects younger people, particularly women.  This cancer has a very good prognosis. Follicular cell cancer is less common, has slightly worse prognosis and it can occur in elderly people.

Medullary cell carcinoma is very rare, could be aggressive and sometimes (25%) is hereditary.  Genetic testing might be necessary in patients and their family.

Anaplastic thyroid cancer has very poor prognosis but fortunately is extremely rare

Like with most cancers, the cause is not well unknown.  However, it is very strongly linked to radiation exposure and some genetic mutations.

The commonest symptoms of thyroid cancer are finding a lump in the thyroid or enlarged lymph node in the neck. Large nodules can cause difficulty in swallowing or breathing.  However, many thyroid nodules don’t cause any symptoms and are found incidentally during routine examination or neck scans.

Hoarseness of the voice can be a sign of advanced cancer.

Surgery is usually required to cure thyroid cancer.  Depending on the type of tumour and its size the whole thyroid gland (total thyroidectomy) or sometimes part of it (hemithyroidectomy) will need to be removed. Enlarged lymph nodes with cancer in them will also need to be removed surgically (Lymph node dissection)

After total thyroidectomy thyroxine hormone tablets will need to be taken for the rest of your life.  Regular thyroid function tests need to be performed to ensure adequate suppression of TSH levels.

Some patients will need to have radioactive iodine treatment after surgery.  The dose of radiation is very low and treatment is well tolerated but you will need to stay in hospital for a day or two and stay away from young children and pregnant women for 7-14 days to prevent their exposure to radiation.

Total thyroidectomy is the removal of all thyroid tissue and is a recommended procedure for thyroid cancer. Removal of lymph nodes in the neck is sometimes necessary to be performed in cases of papillary or follicular cancer of the thyroid and recommended for medullary cancer. If your surgeon expects to remove lymph glands it will have been discussed with you.

Near total thyroidectomy is the operation recommended for treating Grave’s disease and multinodular goitre. It involves removal of almost all thyroid, with only a sliver of thyroid left in place to protect parathyroid glands and laryngeal nerves.

Thyroid lobectomy (hemithyroidectomy) involves removal of one of the thyroid lobes and is performed either for large goitres arising from only one lobe or if a nodule is suspected to be malignant but there is no certainty that this is the case. If the thyroid nodule proves to be a cancer on histology, a completion thyroidectomy eg. removal of remaining lobe, may be needed.

Thyroid surgery is performed under general anaesthetic.  No food or drink is allowed for 6 hours before the procedure. 

The operation is performed through a small incision in the lower neck. This is made at the collar line and it follows an existing skin crease. The incision is symmetrical even if the thyroid abnormality is only on one side. The incisions vary in length depending on the size of the nodule and the size and shape of your neck. 

The muscles and the thyroid gland are mobilised and the laryngeal nerves and parathyroid glands are seen and preserved.  At the end of the operation the surgeon may consider it appropriate to leave a small drain tube in the neck.  This will normally be removed on the first or second day after surgery. 

After the operation you will be moved to recovery room and then return to your ward where regular blood pressure, pulse and oxygen levels will be checked.  There will also be a drip in your arm through which fluids and other medications will be given as necessary.

Sometimes the surgeon will insert a drain in the neck which will be removed 24-48 hours after surgery.  This drain is present to drain fluid gathering in the neck that is natural after surgery.  The drain can be removed by a nurse.

You might experience some discomfort and stiffness around the neck and scar after the operation. In the majority of patients’ pain can be adequately controlled with tablets but sometimes injections are necessary.  After surgery you will be encouraged to perform gentle neck exercises to prevent further stiffness.

Immediately after the operation you might feel sore and uncomfortable and have some discomfort when swallowing.  These changes are temporary and self limiting and you will be able to swallow, eat and drink few hours after the operation. 

The average stay in hospital after thyroidectomy is 1-2 nights.  However, you will probably need another 7-14 days off work to recover from it.

After a total thyroidectomy lifelong thyroid replacement is always necessary. Thyroid replacement is a straightforward once a day regime with little requirement for adjusting dosage. Thyroxine tablets are given to replace thyroid hormones but also to suppress thyroid stimulating hormone (TSH), which is a very important part of the treatment for thyroid cancer. 

After half of the gland has been removed only 5-15% of patients will require hormone replacement as the remaining tissue grows and compensates. When the thyroid recovers normal activity there is a risk of failure over the years which requires careful follow up

Thyroidectomy does not affect your ability to have children. Once the thyroid hormone levels are normal after surgery there is no reason not to become parent if it is desired. 

Most thyroid operations are straightforward and associated with few problems, however all operations carry the risk and complications specific for thyroid surgery include:

  • Wound infection
  • Post-operative bleeding
  • Voice change
  • Low calcium
  • Unsightly scar
  • Miscellaneous problems due to anaesthesia, but these are very rare.

Low calcium after total thyroidectomy is caused by damage to the parathyroid glands. Sometimes these changes are only temporary as in most cases parathyroid function recover within days or weeks and rarely permanent. Following total thyroidectomy 10-15% of patients have a temporary and about 5% permanent hypocalcaemia. 

Parathyroid glands are responsible for regulating calcium concentration in the blood. There are usually 4 parathyroid glands and they are closely related to the thyroid. It is normally possible for the surgeon during a thyroid operation to identify and preserve them but some of them can be removed or bruised and they may not function straight away. This may result in low blood calcium levels and you may experience tingling sensations in your hands, fingers, lips or around your nose and toes. Very low calcium can produce muscle cramps and spasms.

If the level of calcium on a blood test after the operation is low you will benefit from treatment with oral calcium and alfacalcidol, an active form of Vitamin D.

The thyroid gland is very close to the voice box (larynx) and recurrent and superior laryngeal nerves, which move vocal cords positioned within it. These nerves are very small and their anatomy could be varied.

There is a slight but real risk of injuring the nerves during surgery which will result in hoarseness and weakness of the voice.  It is possible for the bruised nerves not to work properly straight away but this can recover within hours, days or weeks after surgery.  Cutting the nerve leads to permanent voice change. Careful surgery and the use of the intraoperative nerve monitoring systems reduces the risk of permanent accidental injury to a very low level but cannot absolutely eliminate it.

The incidence of unilateral permanent injury to the recurrent laryngeal nerve is in the range of 1%.  If the single recurrent laryngeal nerve is damaged the voice becomes hoarse.  Often there is a gradual improvement in voice quality but sometimes voice therapy or further surgery is needed. Injury to both nerves is extremely rare (0.1%) but is a serious problem and may require a tracheostomy (a tube placed through the neck into the windpipe).

Injury to the external branch of the superior laryngeal nerve occurs in about 2-5% of thyroidectomies but the precise risk of this complication is unknown.  This injury produces voice fatigue and difficulty in voice projection and the possible decrease in voice range.  Voice quality can improve over time. 

The position of the scar will be explained to you by the surgeon.  The scar runs horizontally low down on the front of the neck, in the same direction as the natural lines of the skin

It usually heals very well and most of the time it is not very noticeable. The scar may become relatively thick and red for a few months after the operation before fading to a think white line.  Very rarely some patients develop a thick, exaggerated scar but this is uncommon.

The most important way to look after your wound is to keep it clean and dry.  During the first week the scar might be a little bit swollen and tender to touch but this should settle.  To make the scar look and heal better you can rub a small amount of cream, such as E45 or vitamin E cream which can soften the scar and improve healing.

Wound infections after thyroid surgery are very infrequent and affect about 1% of patients. Wound infection usually occurs 3-4 days after surgery and presents with red and tender swelling around scar, fever and general unwellness. It is very important to contact your surgeon as soon as you realise that infection might be developing. Urgent treatment with antibiotics is usually needed but in very rare situation an operation to evacuate infected fluid is necessary.

The thyroid is a very vascular gland and many arteries and veins supplying it have to be tied off during surgery. Post-operative bleeding is nowadays very rare and affects fewer than 1% of patients. Even small bleeding after thyroid surgery creates neck swelling which can cause difficulty breathing and swallowing. If this happens the patient needs to be taken back to theatre to evacuate the clot and stop bleeding. This is why we recommend you should stay in the hospital overnight as this complication is extremely rare after 24 hours. Patients taking medications interfering with blood clotting (aspirin, warfarin) must stop them before surgery.

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