Hurthle cells

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Furqan M M. M.B.B.S[2]

Overview

Hurthle cells are also called Askanazy cells. They are the specific cells found in the thyroid gland and are visible on the histopathological picture. They may be present in a variety of thyroid diseases including Hashimoto's thyroiditis and thyroid carcinoma.

Hurthle cells

Hurthle cells are also called Askanazy cells. They are the specific cells found in the thyroid gland and are visible on the histopathological picture. They may be present in a variety of thyroid diseases including Hashimoto's thyroiditis and thyroid carcinoma. These cells are characterized by the following:

• Large, polygonal cells
• Eosinophilic cytoplasm
• Abundance of mitochondria

The significance of Hurthle cells

Hurthle cells are present in the following conditions:

• Hashimoto's thyroiditis
• Grave's disease
• Benign thyroid adenomas
• Follicular thyroid carcinoma

A Hürthle cell (English: /ˈhɪrtlə/) or Askanazy cell (English: /ˌɑːskəˈnɑːzi/) is a cell in the thyroid that is often associated with Hashimoto's thyroiditis as well as benign and malignant tumors (Hürthle cell adenoma and Hürthle cell carcinoma, a subtype of follicular thyroid cancer). This version is a relatively rare form of differentiated thyroid cancer, accounting for only 3-10% of all differentiated thyroid cancers. Oncocytes in the thyroid are often called Hürthle cells. Although the terms oncocyte, oxyphilic cell, and Hürthle cell are used interchangeably, Hürthle cell is used only to indicate cells of thyroid follicular origin.

History

The Hürthle cell is named after German histologist Karl Hürthle, who investigated thyroid secretory function, particularly in dogs. However, this is a misnomer since Hürthle actually described parafollicular C cells. The cell known as the Hürthle cell was first described in 1898 by Max Askanazy, who noted it in patients with Graves' disease.

Histology

Hürthle cells arise from the follicular epithelium. Key features of these oncocytic cells include an eosinophilic granular cytoplasm and a vesicular nucleus with a large nucleolus. A Hürthle cell is larger than a follicular cell, and its cellular material stains pink. Hürthle cells also tend to be large, polygonal cells with distinct cell borders. The cytoplasm of the oncocytes in Hürthle cell adenomas and carcinomas is characterized by an eosinophilic granular nature, which is commonly due to the oncocytes' high content of mitochondria. Some of these cells can contain up to 5,000 mitochondria, which fills the cytoplasm to the point of nearly excluding other organelles. This high amount of mitochondria is reported to be a result of mutations in the mitochondrial DNA. Some scientists have identified these mutations as deletions in the mitochondrial DNA of Hürthle cells found in neoplasms and Hashimoto's thyroiditis.

Clinical significance

Hürthle cell cancer can be separated into Hürthle cell adenoma and carcinomas, which are respectively benign and malignant tumors arising from the follicular epithelium of the thyroid gland. The mitochondrial DNA of Hürthle cell carcinoma contain somatic mutations. Hürthle cell carcinomas consists of at least 75% Hürthle cells. Chronic lymphocytic thyroiditis or Hashimoto's thyroiditis, along with cases of long-standing Graves' disease, show Hürthle cells present.

Diagnosis

Hürthle cell adenomas are more frequent than Hürthle cell carcinomas. It is difficult to differentiate between being benign or malignant Hürthle cell lesions. Hürthle cell carcinomas consists of at least 75% Hürthle cells. Chronic lymphocytic thyroiditis or Hashimoto's thyroiditis, along with cases of long-standing Graves' disease, show Hürthle cells present. Classification is important since widely invasive tumors can have outcomes with a 55% mortality rate.

• Size and growth pattern of the tumor cannot be used to determine malignancy, although larger tumors have a higher incidence of malignancy, Hürthle cell adenomas and carcinomas are differentiated on the basis of capsular and vascular invasion.
• Tumors displaying only capsular invasion tend to behave less aggressively than those with vascular invasion.
• Hürthle cell carcinomas are characterized as either minimally invasive or widely invasive tumors.
• The minimally invasive or encapsulated carcinoma is fully surrounded by a fibrous capsule.
• The widely invasive carcinoma shows an extensive area of both capsular and vascular invasion with the leftover capsule typically difficult to identify.

Treatment

The appropriate diagnosis of the underlying cause of the Hurthle cells in the histological picture directs the treatment.

• Grave's disease and Hashimoto's disease are usually treated for hyperthyroidism and hypothyroidism respectively.
• A non-minimally invasive Hürthle cell carcinoma is typically treated by a total thyroidectomy followed by radioactive iodine therapy.
• A Hürthle cell adenoma or a minimally invasive tumor can be treated by a thyroid lobectomy, although some surgeons will perform a total thyroidectomy to prevent the tumor from reappearing and metastasizing.