Learn about your pathology report:

Hurthle cell adenoma

What is a Hurthle cell adenoma?

A Hurthle cell adenoma is a non-cancerous type of thyroid tumour. It is made up of large pink cells called Hurthle cells that are separated from the normal thyroid tissue by a thin tissue barrier called a tumour capsule. The tumour often forms a lump in the thyroid gland that doctors call a nodule that can be seen when an imaging procedure called an ultrasound is performed.

Hurthle cells

The thyroid gland

The thyroid is a U-shaped gland located in the front of the neck. The normal thyroid gland is divided into right and left lobes that are connected in the middle by the isthmus. Some people also have another small lobe above the isthmus called the pyramidal lobe.

Anatomy thyroid gland

The thyroid gland makes thyroid hormone. 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 centre of follicles.

Normal thyroid follicles

How do pathologists make this diagnosis?

The diagnosis of Hurthle cell adenoma can only be made after the entire tumour is removed and sent to a pathologist for examination under the microscope. However, most patients undergo a minor surgical procedure called a fine-needle aspiration or FNA before the tumour is removed completely. This procedure uses a very thin needle to remove a small amount of tissue from the abnormal area of the thyroid gland. This tissue is then examined by a pathologist under the microscope. The FNA biopsy provides a preliminary diagnosis that helps guide further management.

Hurthle cell adenoma is made up of large pink Hurthle cells. The Hurthle cells are typically arranged in small to medium-sized follicles. When viewed under the microscope, the cells in a Hurthle cell adenoma can look very similar to the cells in a type of thyroid cancer called Hurthle cell carcinoma. The only difference between a Hurthle cell adenoma and a Hurthle cell carcinoma is that all of the abnormal cells in a Hurthle cell adenoma are separated from the normal thyroid gland by a thin tissue barrier called a tumour capsule. In contrast, in a Hurthle cell carcinoma, the tumour cells have broken through the tumour capsule and have entered the surrounding normal thyroid gland. Pathologists describe this as tumour capsule invasion. For this reason, the diagnosis of Hurthle cell adenoma can only be made after the tumour has been removed completely. By examining the entire tumour capsule, your pathologist can make sure that there is no evidence of tumour capsule invasion.

Hurthle cell adenoma

Hurthle cell carcinoma

Tumour size

This is the size of the tumour measured in centimetres (cm). The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.

Post biopsy changes

The FNA performed before the tumour is removed fully causes changes in the thyroid gland and the tumour that can be seen under the microscope. Your pathology report may describe these changes as post-biopsy changes or FNA-like changes.

These changes include hemorrhage (bleeding), cystic degeneration (the development of holes or spaces in the tissue), and atypical (abnormal) looking cells. All of these changes are expected non-cancerous findings in a Hurthle cell adenoma.

by Jason Wasserman, MD PhD FRCPC (updated July 16, 2021)
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