Hurthle Cell Adenoma: Understanding Your Pathology Report

Section Editor: Jason Wasserman MD PhD FRCPC
May 31, 2026

Hürthle cell adenoma is an older name for a benign (non-cancerous) thyroid tumor that is now called oncocytic adenoma of the thyroid gland. The name was changed in the 2022 World Health Organization (WHO) classification of thyroid tumors. Both terms describe the same tumor, but the newer name is now preferred. The older name Hürthle cell adenoma may still appear on pathology reports during the transition between the two names.

For complete information about this diagnosis, including how it is made, what it looks like under the microscope, treatment, prognosis, and follow-up, please see our dedicated article on oncocytic adenoma of the thyroid gland.

A brief summary

Oncocytic adenoma of the thyroid gland (formerly Hürthle cell adenoma) is a benign tumor that arises from follicular cells, the cells in the thyroid gland that normally produce thyroid hormone. The tumor is made up mostly of large pink cells with abundant mitochondria, called oncocytic cells. These cells were once called Hürthle cells, which is where the older name came from.

Two key features define the diagnosis:

  • More than 75 percent of the tumor cells are oncocytic.
  • There is no evidence of invasion — meaning the tumor cells have not crossed through the tumor’s capsule into the surrounding thyroid tissue and have not entered any blood vessels. The presence of invasion would change the diagnosis to oncocytic carcinoma of the thyroid gland (formerly Hürthle cell carcinoma).

Because the entire capsule must be examined under the microscope, the diagnosis cannot be made from a small needle biopsy sample (called a fine needle aspiration biopsy). The final diagnosis is made after the tumor has been surgically removed, usually by a lobectomy (removal of one lobe of the thyroid).

Why was the name changed?

The WHO 2022 classification replaced Hürthle cell adenoma with oncocytic adenoma of the thyroid gland for two main reasons:

  • The term oncocytic more accurately describes what the cells look like and why they have their distinctive pink appearance (their cytoplasm is packed with energy-producing structures called mitochondria).
  • Research has shown that oncocytic thyroid tumors have unique molecular features that set them apart from other thyroid tumors. They are now considered a distinct group rather than a variant of follicular adenoma.

The same name change also applies to the cancerous counterpart: Hürthle cell carcinoma is now called oncocytic carcinoma of the thyroid gland.

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