A thyroid “nodule” is a localized “swelling” or “lump” within the thyroid gland. A thyroid nodule can be single or multiple in which case it is part of a “multinodular goitre”. Multinodular goitre is not uncommon in older people and often causes no symptoms. Single nodules are also common, affecting perhaps 5% of the population – although most of those affected are not aware that there is anything wrong with their thyroid gland. The percentage of the population with thyroid nodules is higher if ultrasound is used to detect their presence. There are many causes of single nodules in the thyroid gland. Although cancer is uncommon, it is the main reason to investigate thyroid nodules.
Types of Thyroid Nodules
The single thyroid nodule is usually one of four things:
- a fluid-containing cyst;
- a degenerated benign tumour/adenoma;
- a slowly growing adenoma;
- a small percentage is malignant(5-10 %).
Because the rest of the thyroid gland is usually normal, thyroid function is normal and patients are not hyper- or hypothyroid.
Thyroid nodules are usually small and painless. They do not cause any pressure effects in the neck. Most patients do not even notice the swelling. The swelling is found by their doctors when they have routine medical checkups or are examined for other conditions. Thyroid nodules are usually firm, smooth, and easily felt through the skin if they are large enough . Most nodules over 2 cm are palpable during a careful examination of the neck area. Smaller nodules are usually only detectable by ultrasound. The rest of the gland feels normal.
Thyroid nodules that are cancerous can be hard and associated with enlarged lymph nodes in the neck if the tumour has spread. However, physical examination alone cannot suffice to distinguish between benign and malignant nodules.
Laboratory Tests and Thyroid Biopsy
One of the most important tests for nodules is the ultrasound which determines size, shape, and whether it is solid or liquid. In nodules with normal or increased TSH levels, the next step is to carry out a fine needle biopsy of the thyroid nodule. Cells and fluid are removed from the thyroid gland and examined by a pathologist to determine whether this is benign or malignant. A needle may also be placed into a thyroid cyst and fluid is drawn into the syringe. Very occasionally, pus is drawn, indicating that the nodule is a thyroid abscess. If a nodule is associated with decreased TSH levels the next step is to carry out a thyroid scan and iodine uptake in the nuclear medicine department. If the nodule traps iodine (also called “hot nodule”) appropriate treatment for hyperthyroidism should be undertaken. If the nodule does not take up radioactive iodine, also called “cold” nodule, a thyroid biopsy should be performed.
Treatment of thyroid nodules depends on the nature of the nodule. The treatment for non malignant nodules consists mainly of surveillance. Follow up of such nodules consists mainly of surveillance. If the nodule enlarges, the biopsy may be repeated and surgery can be proposed. Periodic surveillance of TSH levels is also warranted.
If the investigations show cells that are “suggestive of malignancy” then the nodule must be removed. If, at operation, pathological examination shows the nodule to be malignant then the rest of the thyroid is usually removed and additional treatment may be necessary. For those nodules whose biopsy shows “malignant cells” the entire thyroid gland is removed and further treatment may be proposed (please refer to the thyroid cancer health guide).
Treatment and Prevention of Recurrence
It was previously thought that treatment with thyroxine will prevent the nodules from progressing in size and /or recurring in the remaining tissue. In the absence of an increased TSH level, treatment with thyroxine is not supported by current data.
Treatment of Benign Nodules
Benign thyroid nodules may be treated with thyroid hormone (e.g. thyroxine) to shut “off” TSH and thereby hopefully shrink the nodule. Patients treated in this way must be examined every six months. As long as the nodule does not enlarge, there is no concern. However, if the nodule enlarges despite treatment with thyroxine, this would suggest that it may have become malignant and should be removed . It should also be emphasized that most benign nodules do not shrink with thyroxine therapy, and fewer such nodules are treated in this fashion. Cysts never respond to thyroxine.
Irradiation of the Thyroid and Neck Region
In the 1940’s and early 1950’s, many children were given X-ray treatment for a variety of benign conditions of the thymus, adenoids, tonsils, and skin.
It was later realized that this irradiation affected the thyroid gland. In some studies up to 25% of such people eventually developed thyroid nodules, one third of whom developed thyroid cancer.
Thyroid nodules which appear following irradiation should be investigated by clinical examination, thyroid ultrasound and biopsy just like other nodules. However if there is a suspicion of malignancy, the thyroid nodule should be removed and the rest of the gland examined carefully for the presence of thyroid cancer.
What about people who received irradiation but who do not have a nodule? It is important that such people be carefully examined because of the high likelihood of a nodule developing.
When there are many nodules in the thyroid gland, it is difficult to be certain as to whether or not one of these nodules is malignant. Ultrasound can help identify nodules with worrisome features. In the absence of such features, the biggest nodule is usually biopsied. Thyroxine will only rarely cause multinodular goitres to shrink, as there are usually areas of either degeneration or autonomy or both. If the goitre is large, or if it is enlarging over time, surgical removal can be indicated. Sometimes radioactive iodine is administered for the patient whose multinodular goiter becomes “toxic” because of increased thyroid hormone production.