Thyroid Nodules

There are many different types of thyroid nodules, which are divided into two main categories: benign and cancerous. A benign nodule is non-cancerous. A nodule that is malignant shows the presence and/or growth of cancer cells. Different types of nodules include:

• Colloid nodule: The most common type of benign nodule, consisting of enlarged growths of normal thyroid tissue. Even if colloid nodules should grow, they remain localized to the thyroid.
• Follicular adenoma: Another type of benign nodule
• Thyroid cyst: Areas of the thyroid that contain fluid, and sometimes a combination of fluids and solids (complex cysts). Ranging from less than 1/3 inch in diameter to more than one inch, if a cyst is filled with fluid only, it is benign. If constituted by a combination of fluids and solids, a cyst can be malignant.
• Inflammatory nodule: Caused by thyroiditis, a chronic inflammation of the thyroid gland. These nodules are generally painless. A rare type of thyroiditis, subacute thyroiditis is the only one to cause pain in the thyroid gland.
• Thyroid cancer/thyroid carcinoma
• Multinodular goiter: An enlargement of thyroid gland is a goiter. Enlargement can be caused by thyroid nodules, in which case it is known as a multinodular goiter, which may cause tightness in the throat, voice changes, as well as difficulty breathing or swallowing.
• Hyperfunctioning thyroid nodule (toxic adenoma, toxic multinodular goiter, Plummer's disease): Nodules that produce their own thyroid hormones, irrespective of the TSH made by the pituitary gland (which regulates the thyroid). Hyperfunctioning thyroid nodules produce high levels of thyroxine which results in low levels of TSH. Another cause of an overactive thyroid gland is a genetic defect of TSH receptors in the thyroid gland.

Thyroid nodules are very common in the general population. They are picked up in about five percent of individuals during a physical examination. Half the population's thyroid nodules are found by ultrasound or other imaging studies of the thyroid gland. About 95 percent of these nodules are benign and five percent are malignant. Most malignancies are called well-differentiated thyroid cancer. Well-differentiated thyroid cancer includes papillary carcinoma of the thyroid which accounts for 80 percent of thyroid cancers, and follicular carcinoma of the thyroid which accounts for approximately 10 percent of such cancers. Another five percent of cancers are composed of medullary carcinoma of the thyroid, which may run in families, and a very small percentage are highly malignant anaplastic carcinomas.