thyroid oncocytic anomalies

Examples

 thyroid oncocytic tumors

• thyroid oncocytic adenoma
• thyroid oncocytic carcinoma

Oncocytic change

 Oncocytic change is defined as cellular enlargement characterised by an abundant eosinophilic granular cytoplasm as a result of the accumulation of altered mitochondria.

 This phenomenon of metaplasia occurs in inflammatory disorders, such as thyroiditis, or other situations that result in cellular stress.

 The proliferation of oncocytes gives rise to oncocytic hyperplastic nodules and oncocytic neoplastic nodules.

In the thyroid, Hürthle cells are found in a variety of conditions and, therefore, are not specific for a particular disease. Individual cells, follicles, or groups of follicles may show Hürthle cell features in irradiated thyroids, in aging thyroids, in nodular goitre, and in chronic lymphocytic thyroiditis, in addition to that seen in long standing autoimmune hyperthyroidism (Graves’ disease). In some of these situations, one can often find an entire nodule composed of oncocytes, and the distinction of hyperplasia from neoplasia can be problematic.

In chronic lymphocytic thyroiditis, follicular cells can show extensive oncocytic change, which is most pronounced in areas of inflammation. The nuclei can exhibit crowding, clearing, irregular contours, and grooves, mimicking papillary carcinoma.

Nodules of oncocytes in the setting of chronic lymphocytic thyroiditis or in nodular hyperplasia may be hyperplastic or neoplastic. The distinction can be extremely difficult or impossible.

The identification of oncocytic change in thyroid tumours has led to major controversies. Because some lesions that were called benign developed metastases, there were proponents of the view that all oncocytic tumours of the thyroid should be treated as malignancies.

Numerous studies indicated that the criteria that apply to follicular tumours of the thyroid also distinguish malignant from benign Hürthle cell lesions.

These included capsular and vascular invasion. Moreover, studies showed that the larger the Hürthle cell lesion, the more likely it is to show invasive characteristics; a Hürthle cell tumour that is 4 cm or greater has an 80% chance of showing histological evidence of malignancy.

Nuclear atypia, which is the hallmark of the Hürthle cell, multinucleation, and mitotic activity were not considered useful for predicting prognosis.

However, there remained a group of Hürthle cell lesions that were not invasive and were considered to be Hürthle cell adenomas, yet they gave rise to lymph node metastases. These lesions can be a reflection of the failure to recognise oncocytic follicular variant papillary carcinomas.

See also

 thyroid follicular lesions / thyroid follicular anomalies

• thyroid follicular hyperplasia
• thyroid follicular neoplasia / thyroid follicular tumors

 proliferation of thyroid follicular epithelial cells
 neoplastic transformation of thyroid follicular epithelial cells