by Jason Wasserman MD PhD FRCPC
October 24, 2022
An oncocytic adenoma is a non-cancerous type of thyroid tumour. It is made up of large pink oncocytic 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 called a nodule. Another name for this tumour is Hurthle cell adenoma.
Most oncocytic adenomas present as a painless lump or growth on the front of the neck. For many patients, the tumour is discovered incidentally (by accident), when imaging of the neck is performed for another reason. Large tumours may cause difficulty swallowing or breathing, especially when lying down.
Radiation exposure as a child and iodine deficiency are both associated with an increased risk of developing an oncocytic adenoma. However, for most patients, the cause remains unknown.
Encapsulated means that the tumour is surrounded by a thin layer of tissue called a capsule. The capsule separates the cells in the tumour from the cells in the normal thyroid gland.
In order to make the diagnosis of an oncocytic adenoma, the entire tumour must be removed and sent to a pathologist for examination under a microscope. Your pathologist will then make sure that the tumour cells have not spread past the tumour capsule into the surrounding normal thyroid gland and that no tumour cells are seen in a blood vessel. Because the entire tumour capsule must be examined, the diagnosis cannot be made after only part of the tumour is removed in a procedure called a fine needle aspiration biopsy (FNAB).
The cells in an oncocytic adenoma and an oncocytic carcinoma look very similar when examined under a microscope. However, in contrast to an adenoma, the cells in an oncocytic carcinoma have broken through the tumour capsule and spread into the surrounding thyroid gland. Pathologists describe this as tumour capsule invasion.