Family doctor

What is the thyroid gland?

The thyroid gland is a small organ in the midline of the neck, just below the Adam's apple. It consists of a right and left lobe joined across the front of the trachea (windpipe) by a narrow bridge of thyroid tissue called the isthmus

The job of the thyroid gland is to make a hormone called thyroxine, the gland requires a small amount of iodine in the diet to produce thyroxine. Because New Zealand soil is deficient in Iodine it is put into our table salt. A normal amount of thyroxine is required for normal physical and mental development and all newborn babies in New Zealand are screened at birth for the presence of possible thyroid hormone deficiency.

In adults, thyroxine keeps cells and tissues working at just the right metabolic rate.

Too much thyroxine put out by an overactive thyroid causes an illness with a high metabolic rate called hyperthyroidism. The symptoms of this condition include tremor, heat intolerance, irritability, increased energy, poor sleep, weight loss and frequently, bulging eyes.

Too little thyroxine from an under-active gland causes an illness with a low metabolic rate called

hypothyroidism. This condition causes tiredness, weight gain, swelling and slowness of speech and thinking. A simple blood test to measure the level of thyroxine in the blood is used to diagnose these conditions.

Hyperthyroidism can be treated three different ways: Firstly drugs to block the release and effects of the hormone can be used. Secondly, it can be treated by radioactive iodine which is taken up by the thyroid and which destroys the gland. Lastly, surgical removal of the thyroid is sometimes performed to treat this condition. Details of thyroid surgery will be discussed later in the article.

Hypothyroidism is simply treated by taking thyroxine tablets once a day.

Diagnosis

If you have been referred for diagnosis of a thyroid lump, after an initial examination by a specialist, you may be assessed by one or more of the following methods.

1. An ultrasound scan may be requested to measure the shape of the thyroid and to look for nodules or cysts within the gland. This is a painless test which uses the principle of echoes to assess internal tissues and especially whether tissues are solid or fluid (cystic).

2. A thyroid scintigram or isotope scan. This test measures the rate of function of the gland. It requires an injection into your vein of a tiny dose of a radioactive substance which is uniquely taken up by your thyroid. The isotope emits gamma rays which are detected by a gamma camera. Active nodules show up as "hot" with increased activity whereas "cold" nodules are inactive. Most thyroid nodules are cold.

3. Fine needle aspiration biopsy (FNA). This is an extremely valuable test for diagnosing thyroid lumps. A small sample of cells or fluid is removed from the thyroid gland by passing a needle through the nodule or cyst in the gland. The aspirate is then examined under the microscope and the type of cells making up the swelling can be seen. The test is usually very accurate. FNA causes about the same amount of discomfort as a regular blood test. Side effects are rare and are usually limited to slight discomfort on swallowing for 24 hours and trivial bruising of the skin.

Thyroid Lumps and nodules

Goitre

A visible enlargement of the thyroid gland is called Goitre. There are several causes of goitre and they can affect the thyroid in different ways. The entire gland may be involved or there may be single or multiple nodules or lumps. Patients with overactive or under-active thyroid glands can have goitre but most goitres produce a normal amount of thyroxine and there is no increased or decreased activity. In this situation, the process by which the gland converts iodine into thyroxine is abnormal and the gland increases in size to keep up normal production of the hormone.

Goitres can become very large and cause pressure on the windpipe (trachea) and swallowing tube (oesophagus). This can result in shortness of breath, voice change, cough, increased pressure sensation in the neck and sometimes difficulty swallowing.

Surgery to remove the thyroid gland is usually necessary to treat large goitres that are causing symptoms. Surgery is also necessary where there is a suspicion of thyroid cancer in an enlarged thyroid gland and where the swelling is causing cosmetic deformity.

Single nodule

A single swelling or lump (nodule) in the thyroid gland is a special form of goitre. The majority (90%) of the nodules are not cancerous but either simple swellings of fluid (cysts) or benign growths of thyroid tissue with no tendency to spread or invade structures.

The remaining 10 percent are usually a very low-grade form of cancer, which is almost always completely curable. There are a very small number of nodules that turn out to be a more aggressive form of thyroid cancer, these occur in special situations and are very rare.

Frequently the lumps are not single but multiple and part of an innocent, non-cancerous condition called multinodular goitre, which just means that several swellings are present. Multinodular goitre is the condition that causes generalised enlargenment of the thyroid and can lead to compression.

Cysts

Cysts ( fluid collections) in the thyroid are common. Frequently they are present without the patient noticing but sometimes they can enlarge so that they can be felt. Cysts can be diagnosed by ultrasound or by needle aspiration. Common practice is to use needle aspiration to empty the cysts of fluid. Sometimes doing this once is enough to make the cyst disappear. The aspiration may be repeated if the cyst returns however if the cyst returns after three or more attempts at aspiration removal of the thyroid lobe may be necessary.

Colloid nodules

These are benign nodules made up of thyroid tissue that have become enlarged. They can be single or multiple and can sometimes become very large. They can generally be diagnosed on needle biopsy however sometimes they can look similar to thyroid cancers on FNA and surgical removal may be recommended. Surgery is also necessary if the nodule becomes large and causes compressive symptoms or if they cause cosmetic deformity. Sometimes the nodules can be overactive these will appear "hot" on scintiscan and can cause hyperthyroidism.

Thyroid Tumours

Non-cancerous tumours (Adenomas)

These tumours are caused by an abnormal growth of thyroid follicle cells. They have no capacity to spread or cause destruction of tissue but they cannot be differentiated from one of the types of thyroid cancer on FNA. Surgery is usually recommended for diagnosis. The lobe of the thyroid that has the nodule in it is removed, then while you are still asleep the nodule will be frozen and looked at under the microscope(frozen section). If cancerous cells are seen your surgeon may remove the other thyroid lobe. If it looks benign then the other lobe will be left in.

Thyroid Cancer

The most common thyroid cancers are differentiated thyroid cancers named either papillary or follicular cancer. These make up more than 90% of thyroid cancer and they very rarely cause death. They do have the potential to spread to lymph nodes in the neck and to other parts of the body such as the lungs but even if they do these tumours are still treatable.

There are some rare and more aggressive thyroid cancers which have a tendency to spread to lymph nodes in the neck and other parts of the body. One of these is medullary cancer, which can occur as part of a syndrome of hormonal tumours and is a genetic disease. The other is anaplastic cancer, which occurs in older patients, is very aggressive and often untreatable.

Surgery is the recommended treatment for thyroid cancer and generally the whole thyroid gland should be removed. If the cancer has spread to lymph nodes or if the diagnosis is medullary cancer the lymph nodes in the neck may be removed at the same time.

Frequently radioactive iodine is used following surgery to kill small amounts of thyroid tumour that may have spread to other areas of the body or that remain in the thyroid bed. The radioactive iodine is taken as a drink and has very few side effects but because you become radioactive for a short period your doctor may advise you to stay in hospital for 2- 3 days.

Thyroid Surgery (Thyroidectomy)

Total Thyroidectomy

If the decision has been made to surgically treat your thyroid condition your surgeon will explain that it may be necessary to remove all or only part of the gland. Total thyroidectomy is usually indicated when a nodule is definitely known to be cancerous from an FNA or when the entire gland is enlarged and causing compression. Following a total thyroidectomy you will need to take thyroxine tablets every day to replace the hormone that the thyroid produces.

Hemi-thyroidectomy

When a nodule is only suspicious of cancer on FNA your doctor may recommend having a hemithyroidectomy ie removal of the half of the gland that contains the nodule. Sometimes a pathologist will examine this while you are still under the anaesthetic and a decision made about whether the remaining half of the gland needs to be removed also. Benign conditions affecting one lobe of the gland such as a colloid nodule are also treated by hemithyroidectomy. Thyroxine is usually not necessary following removal of half the gland.

Subtotal-thyroidectomy

In cases where hyperthyroidism is being treated by surgery, sometimes about three quarters of the gland will be removed and a portion will be left behind to continue to function.

Technique

Thyroid surgery is performed under general anaesthesia through a horizontal incision low down in the front of the neck. The incision can vary in length depending on the size of the thyroid gland.

Possible complications of thyroid surgery;

There are several important structures near the thyroid gland that are at risk of injury during this type of surgery. Your surgeon will explain the risks of the operation to you. It is important to note that these complications are rare, they include:

Nerve injury

There are two nerves that are close to the thyroid gland each side that allow the larynx (voice-box) to function. If these nerves, called the recurrent laryngeal nerve and the external laryngeal nerve, are injured during thyroid surgery the character of your voice may change. This is very uncommon and any change is usually temporary.

Low Calcium Levels

During a total thyroidectomy there is a risk of injuring the para-thyroid glands. These four small glands are attached to the back of the thyroid gland and help to control the body's calcium level. If these are injured the calcium levels in your blood can fall. Calcium is important for nerve and muscle function and you may need to take calcium tablets if this happens. Again this is usually a temporary problem and the glands usually start to function again after a period.

Bleeding

As with any surgery bleeding can sometimes occur after the operation. If this happens your neck may swell and you may have to be taken back to the operating room to have the blood drained away.

Pain

Thyroidectomy is not usually a painful operation, there may be some minor discomfort with swallowing and neck movement following surgery for a short time. Simple pain relieving medications are very effective.

You will generally need only one to two days in hospital following this operation and you may need your blood calcium levels checked during your stay. You may have a drain placed into the wound at the time of surgery, this is usually removed after one or two days. You will probably need about a week to recover before resuming normal activities.