Nodular thyroid hyperplasia

What is nodular thyroid hyperplasia?

Nodular thyroid hyperplasia is a non-cancerous type of growth involving the thyroid gland. The abnormal growth can affect one-half of the gland (one lobe) or the entire gland (both lobes and the isthmus). Patients with this condition may notice a lump in their thyroid gland or that their entire thyroid gland is enlarged. Doctors call these lumps thyroid nodules. Nodular thyroid hyperplasia is the most common cause of nodules in the thyroid gland.

The thyroid gland

The thyroid is a small U-shaped gland located in the front of the neck. It is made up of two halves, called lobes, which lie along the trachea and are joined together by a narrow band of thyroid tissue, known as the isthmus.

Anatomy thyroid glandThe function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormone. Once made, the thyroid hormone is released into the bloodstream and transported throughout the body where they control the body’s metabolism (e.g. the conversion of oxygen and calories to energy).

Most of the cells in the thyroid gland are called follicular cells. The follicular cells connect together to form small round structures called follicles. Thyroid hormone is stored in a material called colloid which fills the center of follicles.

Normal thyroid follicles


Ultrasound and fine-needle aspiration

Doctors will often recommend a test called an ultrasound for patients with a lump in their thyroid gland or if the entire gland is enlarged. This test allows the doctor to see inside the thyroid gland. The ultrasound also allows the doctor to remove a small sample of tissue in a procedure called a fine needle aspiration (FNA). This tissue is sent to a pathologist who examines it under the microscope.

How do pathologists make this diagnosis?

The diagnosis of nodular thyroid hyperplasia can be made after part or all of the thyroid gland is surgically removed and sent to a pathologist for examination. The examination involves looking at the thyroid gland with and without a microscope. When examined without a microscope, the thyroid gland looks larger than normal and light-coloured nodules can be seen replacing the normal dark brown thyroid tissue.

When examined under the microscope, nodular thyroid hyperplasia is made up of abnormal follicles that range in size from small to very large. The growth causes the thyroid gland to become divided into small round nodules. The follicular cells in these abnormal follicles look very similar to the follicular cells in the normal thyroid gland.

Nodular thyroid hyperplasia

Adenomatoid nodules

Some pathology reports will use the word adenomatoid to describe the nodules seen in nodular thyroid hyperplasia. Adenomatoid means that the nodules looked similar to a non-cancerous type of growth called a follicular adenoma. Unlike follicular adenomas, adenomatoid nodules are not completely surrounded and separated from the normal thyroid tissue by a thin layer of tissue called a capsule. The word dominant is used to describe the largest adenomatoid nodule.

Degenerative change

A thyroid gland that is enlarged as a result of nodular thyroid hyperplasia will show signs of injury that pathologists describe as degenerative change. When examined under the microscope these changes include hemosiderin (old blood), fibrosis (scar), and the development of small open spaces called cysts.

Fine needle aspiration changes (FNA)

If you had an FNA performed prior to having your thyroid gland removed, your pathologist will be able to see the changes caused by the needle when the tissue is examined under the microscope. These changes usually include bleeding and the formation of a scar along the path of the needle. If your pathologist is unsure if you had an FNA performed before the thyroid gland was removed, they may describe these changes as “FNA-like”.


Pathologists use the term metaplasia to describe a group of cells that have changed from one specialized type of cell into another. Metaplasia is a non-cancerous change. There are two types of metaplasia that are commonly seen in nodular thyroid hyperplasia.

  • Oncocytic metaplasia – The normal follicular cells have increased in size and the body of the cell looks bright pink. In the thyroid gland, these bright pink cells are also called Hurthle cells.
  • Squamous metaplasia – The normal follicular cells have turned into specialized cells called squamous cells which are normally found on the surface of the skin and the inside of the mouth.

Reactive atypia

Pathologists use the term reactive atypia to describe follicular cells that look abnormal in shape, size, or colour. Reactive atypia can be caused by inflammation or prior fine-needle aspiration. Reactive atypia is a non-cancerous change that is commonly associated with nodular thyroid hyperplasia.

Other names for nodular thyroid hyperplasia

Other names for nodular thyroid hyperplasia include nodular thyroid disease, nodular follicular disease, and adenomatous hyperplasia. Non-pathologists use the word goiter to describe the changes caused by nodular thyroid hyperplasia.

by Jason Wasserman MD PhD FRCPC (updated September 20, 2021)
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