Adenomatoid nodule of the thyroid gland

by Jason Wasserman MD PhD FRCPC
June 18, 2025

An adenomatoid nodule is a benign (noncancerous) growth that develops in the thyroid gland. The thyroid gland is a small, butterfly-shaped organ in the front of the neck that produces hormones to regulate the body’s metabolism. Adenomatoid nodules are part of a group of thyroid conditions known as nodular thyroid disease.

These growths are called “adenomatoid” because they closely resemble another type of benign tumour called a follicular adenoma. However, adenomatoid nodules differ because they typically do not have a complete capsule (a thin layer of fibrous tissue) surrounding them. Instead, they blend into the normal thyroid tissue around them.

Adenomatoid nodules are most commonly seen in younger women, but they can occur at any age.

What causes an adenomatoid nodule?

The exact cause of adenomatoid nodules is not completely understood, but several factors appear to be involved. These factors include:

• Hormonal imbalances: Changes in hormone levels can stimulate the thyroid gland, causing it to produce more thyroid tissue.

• Iodine deficiency: A lack of iodine, an essential nutrient for thyroid hormone production, can cause the thyroid gland to become enlarged and form nodules.

• Genetic factors: A family history of thyroid disease or nodules can increase the risk.

These factors are thought to trigger the thyroid gland to overgrow in specific areas, creating nodules. This growth is usually the gland’s attempt to maintain a normal hormone supply.

What are the symptoms of an adenomatoid nodule?

Most people with adenomatoid nodules do not have any noticeable symptoms, especially if the nodules are small. These small nodules are usually discovered by chance during imaging tests or routine medical examinations.

Larger nodules, however, can cause symptoms because they press on structures in the neck. These symptoms include:

• A lump or visible swelling in the front of the neck.

• Difficulty swallowing, especially solid foods.

• Discomfort or a sensation of pressure in the neck.

• Difficulty breathing, particularly when lying down or exercising.

Thyroid function usually remains normal with adenomatoid nodules, but in some cases, thyroid hormone levels can be increased (hyperthyroidism) or decreased (hypothyroidism), resulting in symptoms like fatigue, weight changes, anxiety, or changes in heart rate.

Association with nodular follicular disease

Adenomatoid nodules are part of a broader condition called nodular follicular disease of the thyroid gland, which includes:

• Solitary thyroid nodules: Single nodules that grow independently.

• Multinodular goiter: A condition in which multiple nodules develop throughout the thyroid gland, causing enlargement of the thyroid gland (a goiter).

People with nodular follicular disease often have multiple adenomatoid nodules, which vary widely in size, appearance, and level of thyroid activity.

How is this diagnosis made?

Your doctor may initially suspect an adenomatoid nodule based on symptoms or a physical examination, where the thyroid gland feels enlarged or uneven.

To confirm the diagnosis, your doctor may recommend an ultrasound of the thyroid gland, which provides a clear picture of the size and appearance of any nodules.

A biopsy procedure called a fine needle aspiration (FNA) may be performed. In this procedure, a small needle is used to remove cells from the nodule. A pathologist examines these cells under a microscope. An adenomatoid nodule typically appears benign on this examination. If the results of the biopsy are unclear or if the nodule is large, surgery may be recommended to remove all or part of the thyroid gland for further examination.

What does an adenomatoid nodule look like under the microscope?

When a pathologist examines an adenomatoid nodule under the microscope, it typically appears as a rounded growth that is well-defined from the surrounding normal thyroid tissue. Often, a partial capsule (a thin, fibrous barrier) may surround the nodule, but usually, this capsule is not complete.

Inside the nodule, there is an increased number of follicular cells (the normal cells that produce thyroid hormones). These follicular cells form enlarged follicles known as macrofollicles. The macrofollicles contain colloid, a thick, gel-like substance produced by the thyroid gland, which is darker and more abundant compared to normal thyroid tissue. These characteristics help pathologists distinguish adenomatoid nodules from other thyroid conditions.

What is the difference between an adenomatoid nodule and follicular adenoma?

Although adenomatoid nodules look similar to follicular adenomas, there are important differences:

• Follicular adenoma: This is a completely encapsulated benign tumour that does not merge with the surrounding thyroid tissue. It is a distinct and separate growth.

• Adenomatoid nodule: This is a benign growth that does not have a complete capsule and blends into the surrounding normal thyroid tissue. It often appears as part of a larger nodular disease in the gland rather than as an isolated tumour.

Can an adenomatoid nodule become cancerous?

Adenomatoid nodules are benign and typically do not become cancerous. However, if a nodule grows quickly, looks suspicious on imaging, or has unusual microscopic features, your doctor may recommend further testing or surgery to rule out the possibility of cancer.

How is an adenomatoid nodule treated?

Many adenomatoid nodules do not require treatment if they do not cause symptoms and appear benign on imaging and biopsy. In such cases, regular follow-up with your doctor, including periodic ultrasounds, is usually recommended to monitor for any growth or changes.

Treatment may be recommended if the nodule is large, causes symptoms, or if there is concern about cancer. Treatment options include:

• Medication: Thyroid hormone suppression therapy (levothyroxine) may sometimes be used to help reduce the size of the nodule, although this is less common today.

• Surgery: Surgical removal of the nodule or part of the thyroid gland may be considered if the nodule is large, causes discomfort, or is suspicious for cancer.

Prognosis

The outlook for people diagnosed with adenomatoid nodules is excellent. Most adenomatoid nodules remain benign and stable over time. Regular medical check-ups help ensure that any changes are detected early and managed appropriately.

Questions to ask your doctor

• Should I have regular follow-up ultrasounds?
• How often should I have my thyroid function checked?

• Are there lifestyle changes I should make?

• Should my family members have their thyroids examined too?