This article will help you read and understand your pathology report for Hurthle cell adenoma of the thyroid gland.
by Jason Wasserman, MD PhD FRCPC, updated December 24, 2020
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.
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.
A Hurthle cell adenoma is a non-cancerous thyroid tumour. It is made up of large pink cells called Hurthle cells. The Hurthle cells come from the follicular cells normally found in the thyroid gland.
The cells in a Hurthle cell adenoma are separated from the normal thyroid gland by a barrier called a capsule. Because the tumour is so well separated from the normal thyroid tissue, it usually forms a lump or nodule that can be felt in the neck when the thyroid gland is examined. The nodule can also be seen when the thyroid gland is examined by ultrasound.
The diagnosis of Hurthle cell adenoma can only be made after the entire tumour is examined by a pathologist. 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 the capsule. In contrast, in a Hurthle cell carcinoma, the tumour cells have broken through the capsule and have entered the surrounding normal thyroid gland. Pathologists describe this as capsular invasion.
Because the entire capsule needs to be examined, the diagnosis of Hurthle cell adenoma can only be made after the tumour has been removed and sent to a pathologist for examination under the microscope. By examining the entire tumour, your pathologist can make sure that there is no evidence of capsular invasion.
A fine needle aspiration (FNA) is a procedure which removes a small amount of thyroid tissue. This tissue is then examined by a pathologist under the microscope.
The tumour cells in a fine needle aspiration tissue sample are larger and more pink than normal, healthy follicular cells. Words that pathologists use to describe these cells include granular, eosinophilic, or oncocytic. Hurthle cells often have round nuclei and a single large nucleolus.
The tumour cells may be seen in groups, connected together as follicles, or as single cells. Most tumours also contain less colloid than the normal thyroid gland.
The fine needle aspiration pathology report will describe the tumour as a Hurthle cell neoplasm, a category which includes both Hurthle cell adenoma and Hurthle cell carcinoma.
This is the size of the tumour measured in centimeters (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.
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 bleeding (hemorrhage), cystic degeneration (the development of holes or spaces in the tissue), and abnormal (atypical) looking cells. All of these changes are normal and expected findings.