The thyroid is a gland located in the neck, and a thyroid nodule is a lump that develops within it. Thyroid nodules are rarely cancerous and are common, with around half of all people aged 50 likely to have at least one. As there are many different types of thyroid nodule, investigations are carried out when one is found. Thyroid scans may show that a nodule is hot, warm or cold. A hot nodule produces excessive amounts of thyroid hormone, a warm nodule makes normal amounts, while a cold thyroid nodule produces little or none.
Inside the thyroid gland, thyroid cells produce hormones which regulate the body's metabolic rate. When part of the thyroid enlarges to form a hot nodule, the cells inside the nodule are making too much hormone. Sometimes, enlargement may be part of an effort by the gland to produce more hormone because, overall, the gland is failing and the level of hormone produced by each cell is too low. This may lead to the formation of a warm or a cold thyroid nodule.
Thyroid cancer most commonly develops in the form of a solitary nodule. A cold thyroid nodule has a higher chance of being malignant, or cancerous, than a warm or hot nodule. Even so, around 95 percent of single nodules are found to be benign, or non-cancerous, when investigated. As well as being formed from an overgrowth of thyroid cells, nodules may consist of cysts, benign tumors or inflamed thyroid tissue.
Investigations aim to provide information about a nodule and to determine whether it is cancerous. Thyroid imaging scans involve the use of radioactive iodine. As the thyroid gland uses iodine to make its hormone, the more active the gland, the more radioactive iodine will be taken up, and this can be evaluated on an X-ray. According to the amount of radioactive iodine represented on the X-ray, a lump may be classed as a hot, warm or cold thyroid nodule. The only way of being certain whether cancer is present is to take a sample of the lump, or what is known as a thyroid nodule biopsy.
Nodule biopsies are usually carried out using a technique called fine needle aspiration, where samples of cells are drawn out of the lump using a needle and syringe. The cells are then examined under a microscope. An ultrasound scan may be used to guide the needle placement. It may be possible to leave alone those nodules which are found to be benign, and which are not growing or causing symptoms. If cancer is discovered, regardless of whether the tumor is a hot, warm or cold thyroid nodule, surgical removal of all, or part, of the thyroid gland is usually necessary.