by Jason Wasserman MD PhD FRCPC
November 22, 2022
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). It is the most common cause of nodules in the thyroid gland.
Other names for this condition include follicular nodular disease, nodular follicular disease, and adenomatous hyperplasia. Non-pathologists use the word goiter to describe the changes caused by nodular thyroid hyperplasia.
Patients with nodular thyroid hyperplasia may notice a lump in their thyroid gland or that their entire thyroid gland is enlarged. Doctors call these lumps thyroid nodules. The lumps typically do not cause pain although very large nodules may cause discomfort by putting pressure on surrounding structures.
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-colored 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.
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.
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.
If you had a procedure called a fine-needle aspiration biopsy (FNAB) 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 “reactive atypia” to describe follicular cells that are abnormal in shape, size, or colour as a result of inflammation or injury caused by a prior fine-needle aspiration biopsy (FNAB). Reactive atypia is a non-cancerous change that is commonly seen in a thyroid gland with nodular thyroid hyperplasia.