Any enlargement of the thyroid gland can be called a goiter. A thyroid nodule is a growth, or lump, in or on the thyroid gland. A patient with a goiter can be either hypothyroid, hyperthyroid, or can have totally normal thyroid function. The presence of a goiter does not indicate how the thyroid gland is functioning.
Some points about goiters and nodules:
- Thyroid surgery (thyroidectomy) for a goiter is not common.
- Goiters that contain either many thyroid nodules (multinodular goiter) or no thyroid nodules are usually not cancerous (malignant).
- Small thyroid nodules are detectable on ultrasound only. These are only a few millimeters in size in general. They usually have minimal clinical significance. The majority of thyroid nodules with bigger size are also benign and usually produce no symptoms at all.
- The majority of thyroid cancers appear as a single thyroid lump. A solitary thyroid nodule with a bigger size.
- Approximately 90% of all solitary thyroid nodules are non-cancerous (benign).
- If a goiter is symmetrically (evenly) enlarged, it is referred to as a diffuse goiter.
Causes of Goiters / Thyroid Nodules
There are five general causes of thyroid gland enlargement (goiters)
- Infection or inflammation
- Growth factors
- Cysts formation
- Obscure or unknown causes
Three common growth factors cause thyroid gland enlargement.
1. The most common is TSH (thyroid stimulating hormone) from the pituitary gland. When thyroid hormone in the blood is low, the pituitary gland secreted TSH, which stimulates the growth of the thyroid gland and release of more thyroid hormone.
2. A second growth factor is an antibody associated with Graves’ disease that duplicates the function of TSH.
3. The third growth factor that will cause the thyroid gland to enlarge is human chorionic gonadotropin (HCG). This hormone is produced during pregnancy.
Thyroid tumors, or growths, occur in 6.4% of females and in 1.6% of males. Most thyroid tumors are benign, but approximately 10% of solitary thyroid nodules are malignant. Multinodular goiters are less likely to be malignant. Although the exact cause of most thyroid tumors is unknown, certain types of radiation will promote their development in both animals and humans.
Inflammation / Infection
Inflammation of the thyroid gland with an accumulation of white blood cells can be seen in many types of thyroiditis. Hashimoto’s thyroiditis is the most common common cause of hypothyroidism in the USA. Infection of the thyroid gland (rather uncommon), also causes accumulation of white blood cells in the thyroid gland. Both inflammation and infection can cause the thyroid gland to enlarge.
Cysts are lumps filled with fluid. Thyroid cysts most commonly result from degeneration of benign tissue in a solid nodule, which subsequently liquefies. It ‘s hard for a doctor to determine from a physical examination whether a thyroid nodule is entirely cystic, partially cystic, or solid. Cysts are much less likely to be malignant than are solid nodules.
Sometimes there is no identifiable cause of a goiter, or the explanation may be so obscure or uncommon that identifying the cause may be too lengthly or costly to pursue. Identifying the cause of a goiter will not necessarily change the patient’s treatment, and at the end of the day, the cause of some goiters will remain unknown.
Diagnostics and Testing
The first and most important point to clarify about a goiter is if thyroid nodules are present. If one or more thyroid nodules are present, then they may be evaluated for the possibility of cancer. If a patient has a goiter with no thyroid nodules, then physicians have little concern about cancer.
A physical examination alone is sometimes inadequate to determine whether thyroid nodules are present. In this circumstance, diagnostic ultrasound can be helpful.
Substernal (thyroid tissue located in the chest behind the breast bone) goiters are always difficult to evaluate completely because of their location. Patients with either substernal or very large goiters may require studies of nearby structures to see if they are involved. These studies might include thyroid imaging, chest x-ray, esophagogram, and CAT scan or MRI of the neck and chest.
Evaluation of Thyroid Nodules
The presence of one or more thyroid nodules in a patient raises concern about the possibility of cancer. Evaluation of a patient with one or more thyroid nodules involves a history, physical examination, thyroid function tests, thyroid structure tests, and possibly thyroid biopsies.
Tests of Thyroid Function and Structure
Thyroid function tests determine whether the patient is hypothyroid, hyperthyroid, or euthyroid (functioning normally). Positive antithyroid antibodies reveal the presence of Hashimoto’s thyroiditis. Some authorities recommend a test for calcitonin, a hormone that is elevated in the uncommon medullary thyroid carcinoma. Each of these blood tests can be helpful in the management of a patient with thyroid nodules. Diagnostic ultrasound is the most reliable method for identifying, characterizing, and measuring thyroid nodules. Nonetheless, diagnostic ultrasound cannot reliably distinguish between benign and malignant disease.
Thyroid imaging using radioactive iodine (I123) determines whether a nodule is hot or non-hot. Hot nodules that take up more radioactive iodine than the surrounding tissue. Fine needle aspiration biopsy (FNAB) is the most reliable and accurate method for distinguishing benign from malignant disease.
The first and most important point to clarify about a goiter is if one or more thyroid nodules are present. If one or more thyroid nodules are present, then they may be evaluated for the possibility of cancer. If a patient has a goiter with no thyroid nodules, then physicians have little concern about cancer.
The size of the goiter and the age of the patient are also important when considering treatment. For example, a young patient with many years to live and a very large goiter may wish treatment. Because of the likelihood that the goiter will enlarge over the course of the lifetime. On the other hand, an older patient with a large goiter that is causing no symptoms may decide not to have any treatment. Particularly if that treatment involves some risk in surgery.
In a patient with a goiter and no thyroid nodule(s), thyroid function tests establish how the thyroid gland is functioning. If the patient is hypothyroid, then therapy with levothyroxine is begun. Levothyroxine will restore the patient to a euthyroid state and sometimes reduce the size of the goiter. If a patient is hyperthyroid, then the hyperthyroidism is treated, which usually results in a reduction in the size of the goiter.
Most goiters and thyroid nodules are benign and are treated nonsurgically. Sometimes surgery is indicated for a goiter because of its large size or troublesome symptoms. A patient with a solitary thyroid nodule should not be overly concerned about thyroid cancer; less than 10% of solitary thyroid nodules are cancerous, and the overwhelming majority of patients with thyroid cancer are successfully treated.