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Benign follicular nodule of the thyroid gland

What does benign follicular nodule mean?

Benign follicular nodule is a term pathologists use to describe a group of non-cancerous conditions in the thyroid gland. This diagnosis is usually made after a procedure called a fine-needle aspiration or FNA. All the conditions in this group are made up of cells that look similar when examined under the microscope.

The following conditions can cause a benign follicular nodule:

  • Nodular thyroid hyperplasia: Nodular thyroid hyperplasia is a non-cancerous type of growth involving the thyroid gland. It is the most common cause of thyroid nodules in adults. Another name for this condition is a goiter.
  • Adenomatoid nodule: Adenomatoid nodule is a non-cancerous type of growth in the thyroid gland. Most adenomatoid nodules develop in association with a condition called nodular thyroid hyperplasia.
  • Nodules in Graves disease: Graves is an autoimmune disease associated with increased production of thyroid hormone (hyperthyroidism). Patients with Graves’ disease often have an enlarged thyroid gland. Multiple nodules of varying sizes are typically found in both lobes.
  • Follicular adenoma: Follicular adenoma is a non-cancerous type of thyroid tumour. The tumour cells are separated from the normal thyroid gland by a thin tissue barrier called a capsule.

Most of the time it is not possible for a pathologist to tell the difference between these conditions when examining tissue removed by fine-needle aspiration. For that reason, the term benign follicular nodule is used in place of a more specific diagnosis.

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.

Thyroid gland

The 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

 

How do doctors make this diagnosis?

Patients with a benign follicular nodule typically have an enlarged thyroid gland. The enlarged thyroid can often be seen or felt on the front of the neck. A special camera called an ultrasound will be used to look inside the gland for any abnormal areas. At the same time, a procedure called a fine needle aspiration will be performed to remove a small sample of tissue. This tissue is sent to a pathologist who examines it under the microscope.

What do the cells in a benign follicular nodule look like under the microscope?

When examined under the microscope, the tissue sample typically shows follicular cells arranged in solid, flat groups called sheets. The follicular cells may also form small, round structures, called microfollicles, but this pattern tends to involve only a small amount of the tissue sample. A variable amount of colloid is typically present in the background.

The follicular cells may be described as having small, round to oval nuclei, uniformly granular chromatin, smooth nuclear membranes, and a moderate amount of cytoplasm. Some of the follicular cells will be larger and bright pink. Pathologists call these Hurthle cells.

In addition, specialized immune cells such as macrophages and lymphocytes may also be seen in the tissue sample. These cells are typically seen in small groups or scattered throughout the background.

benign follicular nodule

All the microscopic features described in this section are non-cancerous changes that support the diagnosis of a benign follicular nodule. However, they cannot be used to distinguish between specific conditions within the group.

What happens next?

Most patients with a diagnosis of benign follicular nodule will not need any additional treatment. However, surgery to remove part or all of the thyroid gland may be required if the enlarged gland starts to put pressure on surrounding tissues. Talk to your doctor about the next steps in your care.

by Adnan Karavelic MD FRCPC (updated September 19, 2021)
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