Patients often appreciate a lump in the anterior neck. Some may complain of shortness of breath, sensation of neck tightness, voice changes, and/or dysphagia. It is important to also assess for symptoms of hyperthyroidism or hypothyroidism (discussed below).

Palpable thyroid nodules can be found in approximately 5 % of the population, and sonographically detectable thyroid nodules can be found in about half of the adult population. The great majority (95 %) of thyroid nodules are benign. Thyroid cancer affects 0.2 % of adults in the United States. The incidence of thyroid cancer has increased by threefold over the past 40 years. Table 11.2 indicates different types of thyroid cancers.

Female gender, exposure to ionizing radiation, and family history of thyroid cancer. MEN-2A, MEN-2B, and familial medullary thyroid carcinoma (FMTC) account for 25 % of medullary thyroid cancer cases and are all related to activating mutations in the RET proto-oncogene, a cell membrane tyrosine kinase. Papillary thyroid cancer is associated with Cowden syndrome, Gardner syndrome, and familial adenomatous polyposis. One-fifth of papillary thyroid cancers are due to RET/papillary thyroid carcinoma (PTC) rearrangements, which create a fusion gene comprised of PTC promoters and the RET tyrosine kinase. An estimated one-third or more are due to mutations in BRAF, a gene encoding a signal transduction protein kinase. Thyroid cancer occurs more frequently in women than men. However, nodules occurring in men and in children or the elderly are more likely to be malignant.

Nervousness, weight loss, heat intolerance, thirst, palpitations, pressured speech, and tremors. Women may have irregular or absent menses. Thyroid storm, a severe type of hyperthyroidism, causes high-grade fever, arrhythmia, GI upset, and can be fatal.

Fatigue, weight gain, lethargy, hair changes, cold intolerance, constipation, difficulty with memory/cognition, impaired libido, and impaired fertility.

To examine the thyroid, stand behind the patient, reach both hands around the patient’s neck, and find the cricoid cartilage with the fingertips of both hands. The cricoid cartilage is the first complete cartilaginous ring below the thyroid cartilage (Adam’s apple). The isthmus of the thyroid is located just a few millimeters below the cricoid. From there, move your fingers laterally to assess the thyroid lobes, checking for symmetry. Asymmetry is often the first clue to the presence of a thyroid nodule. Depress one side of the thyroid to rotate the contralateral lobe forward for a better feel. Do the same on the other side. Then ask the patient to swallow (it can be helpful to offer the patient some water to sip and hold in the mouth until you are ready). Swallowing elevates the thyroid gland. The movement will often reveal a nodule that you did not appreciate before and may reveal an inferiorly located nodule that was previously hidden behind the clavicles. Lastly, run your fingertips with a crawling motion along the sternocleidomastoid muscle bilaterally, to examine for adenopathy.

The thyroid gland moves cranially when a patient swallows, due to its attachment to the trachea via the ligament of Berry. A mass that moves with the thyroid is more likely to originate within the thyroid gland as opposed to some other part of the anatomy (lymph nodes, for instance). In rare circumstances, an aggressive thyroid cancer will become fixed due to local invasion of surrounding structures. This is a worrisome sign.

Flushed face, warm skin, tremor, weight loss with possible muscle wasting, tachycardia, widened pulse pressure, and hyperactive reflexes.

Periorbital swelling with puffy face and extremities, fine hair, loss of the outer aspects of the eyebrows, waxy or clammy skin, and weight gain.

The thyroid contains follicular cells and parafollicular C cells. Follicular cells of the thyroid produce, store, and secrete the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Synthesis of T4 and T3 requires iodide, which the thyroid takes up and stores. T4 is a precursor to T3, which is ten times more potent. The thyroid normally produces 20 % of circulating T3; the rest is converted from T4 in peripheral tissues. These remain protein bound in the circulation, and only the free fraction is active. The parafollicular C cells of the thyroid secrete calcitonin.

Thyroglobulin (Tg) is a glycoprotein housed within thyroid follicles that is a storage form/precursor of T4 and T3. Serum thyroglobulin levels correlate positively with the amount of thyroid tissue, thyroid injury/inflammation, and the TSH level. Thus, serum Tg can be used as a tumor marker during surveillance after initial treatment of papillary and follicular thyroid cancer. Anti-Tg autoantibodies are present in about 20 % of thyroid cancer patients and can interfere with Tg testing.

In general, T4 and T3 regulate basal metabolic rate, growth and development, and sensitivity to catecholamines with effects on many organ systems.

The primitive thyroid gland arises from the medial pharynx, part of the embryologic endoderm. This tissue descends along the thyroglossal duct into the neck and ultimately gives rise to thyroid follicles and colloid. The rostral-most aspect of the thyroglossal duct is the foramen cecum. C cells, which produce calcitonin, arise from the fourth pharyngeal pouch and migrate from the neural crest into the thyroid gland.