Your thyroid gland consists of two lobes that resemble the wings of a butterfly. The lobes are separated by a thin section called the isthmus. The thyroid takes up iodine from food you eat and uses it to manufacture two main hormones, thyroxine (T-4) and triiodothyronine (T-3). These hormones maintain the rate at which your body uses fats and carbohydrates, help control your body temperature, influence your heart rate and help regulate the production of protein. Your thyroid gland also produces calcitonin, a hormone that regulates the amount of calcium in your blood.
Thyroid nodules, or lumps, are quite common, occurring in more the 50% of the world’s population. Moreover, the likelihood of developing a thyroid nodule increases with age and in part represents the aging process of the gland. Radiation therapy is the only known cause of noncancerous and cancerous thyroid nodules. It was commonly used in the mid-1950s and 1069s to treat enlarged tonsils, adenoids, and thymus glands, and to treat acne. Currently, radiation therapy is not used for these conditions. The tendency to develop thyroid nodules may be genetic. Although the gene responsible for thyroid nodules is not known, thyroid nodules run in families. Although most nodules are harmless and do not require any treatment at all, approximately 5% of all nodules are cancerous and therefore require attention. Thyroid nodules occur more frequently in women than in men, however the incidence of cancerous nodules is greatest in men. Despite the low incidence of cancer, all nodules should be evaluated by a physician to determine their status.
Most thyroid nodules are so small that they usually do not cause symptoms and cannot be felt. Larger nodules can cause swelling in the neck. Less common symptoms include:
- Pain and /or a feeling of fullness in the throat.
- Difficulty swallowing because the enlarged thyroid gland is pressing on the esophagus.
- Difficulty breathing because the enlarged thyroid gland is pressing on the windpipe (trachea)
- Nervousness, a rapid and pounding heartbeat, excessive sweating, weight loss, and other symptoms of hyperthyroidism.
- Fatigue, lethargy, depression, memory problems, constipation, dry skin, intolerance of cold, and other symptoms of hypothyroidism.
Just why normal thyroid tissue develops into a nodule isn’t clear, What is known is that several types of nodules can develop in the thyroid gland:
- Colloid nodule. Most thyroid nodules are colloid nodules-benign overgrowths of normal thyroid tissue. You may have just one colloid nodule or many. Although these nodules may grow larger, they don’t spread beyond the thyroid gland.
- Follicular adenoma. This type of nodule also is benign. Unfortunately, doctors can’t distinguish between a benign follicular adenoma and follicular cancer without surgically removing the nodule. Normally, a nonsurgical procedure called fine-needle aspiration (FNA) biopsy is the most sensitive way to determine whether a nodule is benign malignant. But FNA biopsy doesn’t provide a definitive answer in cases of follicular adenomas.
- Thyroid cyst. These fluid-filled areas of the thyroid can range in size from less the 1/3inch to 1 inch or more in diameter. Many thyroid cysts are entirely filled with fluid, but some cysts, called complex cysts, also have solid components, Fluid-filled cysts are usually benign, but complex cysts are sometimes malignant.
- Inflammatory nodule. This occasionally develops as a result of chronic inflammation of the thyroid gland (thyroiditis). One rare type of thyroiditis- subacute thyroiditis- causes severe pain in the thyroid gland. Other types are painless and sometimes occur after pregnancy (postpartum thyroiditis).
- Multinodular goiter- Goiter is a term used to describe any enlargement of the thyroid gland. Several factors can lead to a goiter, including the presence of a number of thyroid nodules. This condition, called multinodular goiter, can cause a tight feeling in your throat and difficulty breathing or swallowing.
- Hyperfunctioning thyroid nodule (toxic adenoma, toxic multinodular goiter, Plummer’s disease). These nodules grow and produce thyroid hormones independent of the influence of thyroid-stimulating hormone (TSH), a substance released by the pituitary gland, which normally regulates the production of thyroid hormones.
- Thyroid cancer. Only about 5 percent of thyroid nodules are cancerous. Although the chances that a nodule will be malignant are small, you’re at higher risk if you have a family history of thyroid or other endocrine cancers, are younger the 20 or older than 60, are a man or have a history of head or neck radiation.
Thyroid nodules are diagnosed through a medical history and physical exam. It is unusual to discover thyroid nodules on your own because they are difficult to feel and usually do not cause symptoms. While history, examination by a physician, laboratory test, ultrasound, and thyroid scans can all provide information regarding a solitary thyroid nodule, the only test which can differentiate benign from cancerous thyroid nodules is a biopsy (the term biopsy means to obtain a sample of the tissue and examine it under the microscope to see if the cells have taken on the characteristics of cancer cells). Thyroid cancer is no different in this situation from all other tissues of the body. The only way to see if something is cancerous is to biopsy it. However, thyroid tissues are easily accessible to needles, so rather than operating to remove a chunk of tissue with a knife, we can stick a very small needle into it and remove cells for microscopic examination. This method of biopsy is called a fine needle aspiration biopsy, or FNA. This procedure may be done in the office if the lump can be felt directly, or may be done with ultrasound localization if the lump is small.
Fine-Needle aspiration (FNA) is the removal of a few clusters of individual thyroid cells by means of a small needle. The cells are put on a slide and examined microscopically by a cytopathologist and the results of this test are usually available within a few days. No test is a perfect test, and fine needle biopsy can very rarely be wrong. About one to five percent of the time, the biopsy result will be benign, but the nodule will actually be a cancer. This mistake is called a false-negative result and usually results from the fact that the needle either missed the nodule or hit part of the nodule that did not have cancer in it. Therefore it is very important to have follow-up even if the initial biopsy report is benign.
A cytopathologist will examine each slide produced from a “FNA and divides the diagnoses into four categories: 1) benign 2) malignant 3) indeterminate and 4) nondiagnostic.
1.Benign. Most nodules are found to be benign. When this is the case, a follow-up physical examination in six months is generally recommended. If the nodule is the same size or smaller after six months, yearly follow-up is then recommended. However, if the nodule has grown within the first six months, a second biopsy is generally recommended and a course of action is determined depending on the results of the second biopsy. There are a few situations in which thyroid surgery may be recommended, even if the biopsy result is benign. If a nodule is so large that it presses on the windpipe and/or the esophagus, it will cause difficulty breathing and/or swallowing food. In these situations, thyroid surgery removes the pressure in this area of the neck. Other people with benign thyroid disease may choose to undergo thyroid surgery for cosmetic reasons. Although the nodule may not be causing symptom, the lump in the throat may make you be self-conscious about the way the neck lump looks and want it removed.
2.Malignant. If an FNA reveal that a nodule is cancerous, surgery is recommended to remove it. The accuracy of a cancer diagnosis by needle biopsy is close to 100%.
3.Indeterminate. Nodules that are diagnosed by FNA as indeterminate or suspicious fall somewhere between benign and cancerous. In this situation, anywhere from 10-60% of these nodules are actually cancerous, but there is no perfect way to tell which ones are benign short of performing thyroid surgery to remove the nodule completely.
4. Nondiagnostic. A nondiagnostic fine needle aspiration biopsy results when there are not enough thyroid cells to make a definite diagnosis. A nondiagnostic diagnosis occurs about 10% of the time because the thyroid nodule can be filled with blood, hard material called calcium or fluid and therefore only sparse cells are obtained at the biopsy. Because up to 10% of these nondiagnostic thyroid nodules are cancers, a repeat fine needle aspiration biopsy is usually recommended in order to make a diagnosis. About half the time, the second biopsy will produce a more definitive diagnosis. If a diagnosis still can not be made after the second biopsy either very close follow-up (in three months) to see if the nodule has grown or thyroid surgery is generally recommended in order to make the definite diagnosis.
Following the FNA the decision will be made with the physician as to whether surgery is indicated or whether the nodule is benign and can be safely followed.
The type of surgery recommended depends on the findings of the FNA:
- Indeterminate or nondiagnostic. The entire thyroid lobe and isthmus containing the nodule would be removed. At the time of surgery the pathologist would examine the nodule and determine if it is benign or malignant. If the nodule is benign then the surgery is complete and the wound would be closed and no surgery done on the other thyroid lobe. If a malignant tumor is present then usually the other lobe of the thyroid is also removed for a total or near total thyroidectomy (see section on Thyroid Cancer for more complete description). Under this situation the patient would need life long thyroid replacement. It must be understood that the examination of the nodule at the time of surgery is not 100% accurate. In 10% of the cases the pathologist who initially thought the nodule was benign at the time of surgery will find an area of malignance when he does a more complete examination over the next one to two days. If he does find a malignance further surgery may be needed to remove the remaining thyroid tissue.
- Malignant: With this diagnosis a total or near total thyroidectomy is usually recommended. Some lymph node resection may also be done. The patient would need life long thyroid replacement. Radioactive I131 treatment may also be necessary following the surgery. (See section on Thyroid Cancer for more complete description).
- Large Multinodular Goiter: Usually a total or near total thyroidectomy is recommended. The patient may have symptoms from the enlarged thyroid pressing on the trachea and thus removing the thyroid is important to prevent future breathing problems.
Complications related to the surgery:
1.Injury to the recurrent laryngeal nerve. This nerve runs under the thyroid on each side. If the nerve were injured the patient’s voice would be hoarse. This is not a common injury.
2. Low calcium levels in the body. The calcium in the body is controlled by the parathyroid glands. There are four glands, two on each side under each thyroid lobe. The glands are very small and sensitive. During surgery an attempt is made to find each gland and preserve it. The body only needs ½ if one gland to function normally and so this complication would only occur if a total thyroidectomy where necessary. This complication also is unusual.