Adenomatoid Nodule of the Thyroid Gland: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
May 13, 2026

An adenomatoid nodule is a benign (noncancerous) growth that develops in the thyroid gland. The thyroid is a butterfly-shaped gland at the front of the neck that produces hormones to regulate metabolism. Adenomatoid nodules are the most common type of thyroid nodule and are often part of a broader condition called follicular nodular disease, in which the thyroid contains one or more nodules.

Adenomatoid nodules are called “adenomatoid” because they resemble a different benign thyroid tumor called a follicular adenoma. However, they differ from follicular adenoma in important ways described later in this article. Adenomatoid nodules can occur at any age but are more common in women than in men and become more frequent with age.

What are the symptoms of an adenomatoid nodule?

Most people with adenomatoid nodules have no noticeable symptoms, especially if the nodules are small. Small nodules are usually discovered by chance during imaging tests or routine medical examinations.

Larger nodules can cause symptoms by pressing on structures in the neck. These symptoms may 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 become too high (hyperthyroidism) or too low (hypothyroidism). When this happens, additional symptoms such as fatigue, weight changes, anxiety, or changes in heart rate may develop.

What causes an adenomatoid nodule?

The exact cause of adenomatoid nodules is not completely understood, but several factors appear to play a role:

Hormonal influences. Long-term stimulation of the thyroid by thyroid-stimulating hormone (TSH) and changes in other hormones can encourage areas of the thyroid to grow more than usual.
Iodine deficiency. Iodine is needed to make thyroid hormone. When iodine is in short supply, the thyroid can enlarge and form nodules in an attempt to make more hormone.
Genetic factors. A family history of thyroid nodules or goiter increases the likelihood of developing thyroid nodules or goiter.

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

How is the diagnosis of an adenomatoid nodule made?

The diagnosis usually begins when a thyroid nodule is felt during a physical examination of the neck or seen on imaging done for another reason. A thyroid ultrasound is then used to assess the size, number, and appearance of any nodules. Ultrasound alone cannot diagnose cancer, but it helps identify nodules that may need closer evaluation. If a nodule has concerning ultrasound features or is large, a fine needle aspiration (FNA) biopsy may be performed. In this procedure, a thin needle is used to remove a small sample of cells from the nodule for examination under the microscope. An adenomatoid nodule typically appears benign on this examination. If the biopsy results are unclear or if the nodule is large, surgery may be recommended to remove part or all of the thyroid for a full examination. Blood tests are also often performed to check thyroid hormone levels and confirm that the thyroid is functioning normally.

What does an adenomatoid nodule look like under the microscope?

Under the microscope, an adenomatoid nodule appears as a rounded growth that is fairly well-defined from the surrounding normal thyroid tissue. Often, a partial capsule (a thin layer of fibrous tissue) surrounds part of the nodule, but unlike a true tumor, it is not complete, and the nodule blends into the surrounding thyroid tissue in places.

Inside the nodule, there is an increased number of follicular cells (the cells that normally make thyroid hormone). These cells form enlarged follicles known as macrofollicles, which contain abundant colloid — the thick, gel-like material that the thyroid uses to store hormone. Over time, adenomatoid nodules often also show degenerative changes, including fibrosis (scar-like tissue), cyst formation (fluid-filled spaces), small areas of bleeding, calcifications, and collections of immune cells. These findings are common in long-standing benign thyroid nodules and are not signs of cancer.

How does an adenomatoid nodule differ from a follicular adenoma?

Adenomatoid nodules can look similar to follicular adenomas under the microscope, but they are different conditions:

Follicular adenoma. A completely encapsulated benign tumor that does not blend into the surrounding thyroid tissue. It is a single, distinct growth.
Adenomatoid nodule. A benign growth that does not have a complete capsule and blends into the surrounding thyroid tissue. It is often part of a broader pattern of nodular disease in the gland rather than an isolated tumor.

Distinguishing between the two can sometimes be difficult on a small biopsy sample, which is one reason surgery is occasionally needed to make a final diagnosis.

Can an adenomatoid nodule become cancerous?

Adenomatoid nodules are benign and almost never become cancerous. However, a thyroid that contains adenomatoid nodules can also develop cancer separately, just like any other thyroid. If a nodule grows quickly, feels firm or fixed, looks suspicious on ultrasound, or shows unusual features under the microscope, additional testing or surgery may be recommended to rule out cancer.

What happens after the diagnosis?

Most adenomatoid nodules do not require treatment, and the outlook is excellent. Most nodules remain benign and stable over time. Possible approaches include:

Observation. The most common approach when the nodule is small, the thyroid is functioning normally, and there are no suspicious features. Follow-up usually involves periodic physical examination and, if recommended, an ultrasound to check for any change in size or appearance.
Thyroid hormone medication. If blood tests show that the thyroid is underactive, levothyroxine (a synthetic form of thyroid hormone) may be prescribed. Thyroid hormone suppression therapy, specifically aimed at shrinking nodules, was used in the past but is rarely recommended today.
Treatment for an overactive thyroid. If a nodule is producing too much thyroid hormone, options include antithyroid medication, radioactive iodine, or surgery.
Surgery. Surgery may be considered if the nodule is large enough to cause trouble swallowing or breathing, if there is concern about cancer, or if the biopsy results are unclear.

Any new symptoms, rapid growth of a nodule, or change in voice should prompt evaluation.

Questions to ask your doctor

Do I have a single adenomatoid nodule or several?
Are my thyroid hormone levels normal?
Do I need treatment, or is monitoring enough?
How often should my thyroid be checked with examination, blood tests, or ultrasound?
Are there any features in my report that raise concern for cancer?
Should my family members have their thyroids examined?