Definition of Thyroid nodule:

A thyroid nodule is a growth (lump) in the thyroid gland. The thyroid gland is located at the base of the neck.

Causes, incidence, and risk factors:

Thyroid nodules are growths of cells in the thyroid gland. These growths can be noncancerous (benign) or cancerous (malignant). Some nodules are fluid-filled (cysts), while others are made of thyroid gland cells. Sometimes, what feels like one nodule will actually be a collection of small nodules.

Thyroid nodules are more common in women than in men. A person's chance of a thyroid nodule increases with age.

Only a few thyroid nodules are cancerous. (See: Thyroid cancer)

The following characteristics increase the chances that a thyroid nodule is cancerous:

• A hard nodule
• A nodule that is stuck to nearby structures
• Family history of multiple endocrine neoplasia type II
• Family history of thyroid cancer, especially medullary thyroid carcinoma
• Hoarse voice due to vocal cord paralysis
• Age -- younger than 20 years or older than 70
• History of radiation exposure to the head or neck
• Male gender

Causes of thyroid nodules are not always found, but can include:

• Hashimoto's disease
• Iodine deficiency