Anatomy of the Thyroid Gland
The thyroid gland is located in the lower front of the neck, in front of the windpipe (trachea) and swallowing tube (esophagus). The thyroid has both left and right lobes, connected over the windpipe by an “isthmus”. The left and right lobes are each normally no larger than 2 inches.
Physiology/Function of the Thyroid Gland
The primary function of the thyroid gland is to produce and circulate thyroid hormone. Thyroid hormone, generally speaking, affects our metabolism. It is important in growth, development, energy production, and our body’s energy use. The thyroid gland produces several hormones, including T4, T3, and calcitonin. T4 is the hormone that predominantly circulates in the bloodstream to be delivered to the cells throughout the body. T3 is the active form of the hormone once inside the individual cells of the body. The thyroid gland needs iodine to produce these hormones.
Pathology of the Thyroid Gland
There are many different abnormalities that can occur to disrupt the normal function of the thyroid gland. These include thyroid masses or growths, called “nodules”, thyroid cancer, enlargement of the thyroid gland (referred to as “goiter”), too little thyroid hormone production or “hypothyroidism”, and too much thyroid hormone production, called “hyperthyroidism”.
Thyroid nodules are the most common reason that patients seek the opinion of a head and neck surgeon. Thyroid nodules are very common, present in 4%-8% of adults by physical examination, and even more patients if a thyroid ultrasound is performed. The chances of having a thyroid nodule increase with increasing age. Thyroid nodules can be solitary (only one present), or the thyroid can have a condition known as multinodular goiter, where there is more than one nodule present. Most thyroid nodules are benign. However, most thyroid cancers are discovered by the presence of a thyroid nodule. Overall, the incidence of thyroid cancer in a thyroid nodule is about 10%, but many different factors affect this rate, and evaluation is important to assess for the presence of cancer. Studies show that the larger the nodule, the greater the risk of thyroid cancer.
When a thyroid nodule is discovered, an evaluation is carried out to determine the nature of the nodule(s). This generally includes a visit to your physician, who may refer you to a head and neck surgeon for consultation. This visit typically includes a discussion with the patient and physical examination. Thereafter, commonly performed tests include laboratory evaluation of thyroid hormone levels in the blood, thyroid ultrasound, and often a needle biopsy of the nodule (fine needle aspiration biopsy or “FNAB”) to determine the nature of the nodule.
Thyroid cancer is a form of malignant tumor that begins in the thyroid gland. The incidence of thyroid cancer is growing, probably due to better detection rates. Thyroid cancer is most common in younger adults, nearly two-thirds of cases are diagnosed in people younger than 55 years old, and 2% of thyroid cancers are diagnosed in children. Having a family member who has had thyroid cancer and radiation treatments to the neck are risk factors for thyroid cancer, but most thyroid cancer patients have neither of these risk factors.
There are several forms of thyroid cancer. The most common form is known as papillary cancer. This type of cancer occurs in several variant forms, and makes up 80% of all thyroid cancers. These are usually slow growing, but they can be more aggressive and tend to spread to lymph nodes in the neck, and sometimes elsewhere in the body. The ability to cure these cancers is often very good, especially in patients younger than age 45. Prompt diagnosis and treatment are clearly beneficial.
Follicular cancer of the thyroid, like papillary cancer, is known as a “well-differentiated” thyroid cancer. These cancers generally do not spread to neck lymph nodes, but can spread elsewhere in the body. Hurthle cell cancer is a variant of follicular cancer, which may be a more aggressive subtype, and which accounts for about 3% of all thyroid cancers. Again, follicular cancers of the thyroid have a favorable prognosis (cure rate) if effectively treated. Both papillary & follicular thyroid cancers require lifelong surveillance after diagnosis and treatment.
Medullary cancer and anaplastic cancer of the thyroid are much less common. Lymphoma, a type of cancer more commonly starting in lymph nodes, and other much less common cancers, also occur in the thyroid gland.
Treatment for thyroid cancers generally involves thyroid surgery (“total thyroidectomy”), and commonly a one-time pill of radioactive iodine. This radioiodine treatment is used to obliterate any leftover thyroid cells in the body, and in preparation for a whole body scan to determine any additional involvement of thyroid cancer in the body. Radioactive iodine treatment is usually administered by an endocrinologist.
Other Thyroid Abnormalities
Other common abnormalities of the thyroid gland include thyroid enlargement (“goiter”), which can create compressive symptoms in the lower neck like pressure on the windpipe, shortness of breath, trouble swallowing, and hoarseness. Any of these symptoms typically necessitate a referral to a head and neck surgeon. Hypothyroidism (too little thyroid hormone production) and hyperthyroidism (excessive thyroid hormone production) are common as well. If these are not associated with thyroid nodules, goiter, or compressive symptoms, these conditions are often treated with medications or other nonsurgical treatments.
Laboratory Evaluation of the Thyroid Gland
Laboratory testing of the thyroid gland typically involves thyroid hormone levels and TSH, a pituitary gland hormone which helps in thyroid regulation. Other testing can include thyroid “TPO” or “AMA” antibodies, (which test for Hashimoto’s thyroiditis, the most common form of hypothyroidism), thyroglobulin and thyroglobulin antibodies, and calcitonin levels. Your doctor will arrange for laboratory evaluation of your thyroid gland as indicated.
Radiological Evaluation of the Thyroid Gland
Diagnostic imaging of thyroid gland typically involves an ultrasound (sonogram) performed with sound waves. Other forms of radiological studies are available, but are much less commonly used.
Fine Needle Aspiration Biopsy (FNAB) of the Thyroid Gland
As mentioned earlier, the presence of a thyroid nodule(s) necessitates a visit to your physician, who may refer you to a head and neck surgeon for consultation, physical examination, laboratory evaluation of thyroid hormone levels in the blood, a thyroid ultrasound, and often a needle biopsy of the nodule (“fine needle aspiration biopsy”) to further characterize the nodule. FNAB is performed using several passes of a very skinny needle, is performed an outpatient basis, and is usually done with no anesthesia required or local (numbing medicine injection) anesthesia only. The FNAB can be performed with ultrasound guidance, and various tests can be done on the biopsy specimen, including genetic testing, to increase the accuracy of the biopsy. FNAB results can be positive for thyroid cancer, benign thyroid conditions, “suspicious” for cancer, and inconclusive (“nondiagnostic”). Oftentimes, a decision on whether thyroid surgery is indicated is determined based upon the FNAB result.
Thyroid surgery is indicated for many of the above conditions. Generally, thyroid surgery involves removing one lobe of the thyroid, known as thyroid lobectomy, or the entire thyroid gland, called total thyroidectomy. In cases of thyroid cancer, lymph nodes in the neck are also assessed during thyroid surgery, and lymph node removal surgery is carried out at the same time if indicated.
Thyroid surgery is performed under general anesthesia, through a small incision in the lower neck. Surgery can last 1 ½ – 3 hours and generally requires one, or less frequently, a two-night stay in the hospital. After thyroid surgery, patients have a sore throat for a day or so and have a minimal amount of neck pain. Risks factors for thyroid surgery include hypothyroidism, or the need to take supplemental thyroid hormone pills, hoarseness, and hyperparathyroidism (a reduction in the blood calcium levels after surgery, corrected by taking vitamin D and calcium pills). Thyroid surgery is best performed by a surgeon with special training and who frequently performs thyroid surgery, as complication rates are lower when the operation is performed by an experienced surgeon.
Dr. Rohn and Dr. Gamble are ear, nose, throat, and sinus surgeons with offices located in Plano and Dallas. If you would like to schedule an appointment with our office, please call our Plano office at 972-378-0633 or Dallas office at 214-239-1641.