Hurthle cell neoplasms (HCN) are a distinct subtype of thyroid tumours and are considered a variant of follicular tumours. Although called Hurthle cells, the original cell that Hurthle described was in fact a parafollicular C cell in the thyroid of the dog. It was Askanazy in 1898 who correctly identified the cell that is still known as the Hurthle cell or oncocytic cell.
HCN are encapsulated thyroid tumours that contain more than 75% oncocytic cells, which stain pink under the microscope as they are packed with mitochondria. Hurthle cells can also be found in a variety of other thyroid conditions such as thyroid irradiation, lymphocytic thyroiditis and Graves' disease.They account for 3-10% of all thyroid tumours.
Most HCN patients present with a solitary thyroid nodule that shows Hurthle cells on FNA cytology, which puts these lesions in the THY3 group (see Introduction for an explanation of the THY classification). Like non-HCN follicular tumours, the Hurthle cell tumour can be malignant or non-malignant. The risk of malignancy in HCN is 30%, which is double the rate seen in non-HCN tumours, so that once the diagnosis is made thyroidectomy is mandatory.Diagnosis of malignant HCN relies on the demonstration of capsular and/or vascular invasion at histology, the same criteria used to diagnose malignancy in non-HCN follicular lesions.
HCNmay exhibi tmore aggressive behaviour, with spread to lymph nodes and elsewhere. Unlike other follicular lesions,HCN tends not to take up radioactive iodine. In view of this, although Hurthle cell tumours may indeed be non-malignant, they are probably best treated by total thyroidectomy.An age >50 years at presentation and a tumour size >4cm carry a higher risk of malignancy and these patients should definitely undergo total thyroidectomy.
A cytological slide of Hurthle cell cancer of the thyroid - click to enlarge