Clinical Characteristics

Histology

Hurthle cells are large polygonal, eosinophilic cells with pleomorphic, hyperchromatic nuclei and fine granular, acidophilic cytoplasm, representing an abundance of mitochondria (Fig. 14-1). The individual cells are 10 to 15 pm in diameter and can vary in shape and size from small dumbbells to bizarre giant cells. Hurthle cell neoplasms are encapsulated collections of Hurthle cells (Fig. 14-2). Therefore, the presence of nonencapsulated Hurthle cells does not signify a neoplastic process, because they are commonly associated with Hashimoto's thyroiditis, Graves' disease, and nodular goiters as well as with well-differentiated thyroid cancers.

Hurthle cell tumors continue to be classified as variants of follicular neoplasms. However, Hurthle cell carcinomas

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FIGURE 14-1. Fine-needle aspiration of a thyroid nodule showing an abundance of polygonal-shaped Hurthle cells. Note the pleomorphic hyperchromatic nuclei and granular cytoplasm.

generally behave in a more aggressive manner, metastasizing more frequently, and are less likely to respond to radioactive iodine.8 In addition, Hurthle cell variants of papillary thyroid cancer have been reported with increasing frequency.9 These tumors behave in a manner more similar to Hurthle cell carcinomas, metastasizing and recurring more frequently than papillary carcinomas. Therefore, most believe that Hurthle cell tumors should be classified as a distinct category, with subgroups of follicular and papillary variants.

Demographics

Hurthle cells neoplasms have a peak incidence in the fifth to sixth decades. With advancing age there is an increased chance of a malignancy.10 There is a female preponderance, with reported ratios ranging from 2:1 to 10:1. However, male patients with Hurthle cell neoplasms have a higher relative incidence of carcinoma.

FIGURE 14-2. A Hurthle cell adenoma (A). Note the presence of a thin capsule (C) without any signs of capsular invasion. Most of this neoplasm is composed of Hiirthle cells.

Risk Factors

Up to 39% of patients with Hurthle cell neoplasms in one study reported previous childhood head and neck radiation.11 Previous radiation exposure has also been correlated with an increase in bilaterality and multicentricity of Hurthle cell tumors, as well as an increased incidence of contralateral non-Hurthle cell malignant thyroid lesions. No genetic syndromes have been reported to be associated with Hurthle cell tumors. Other than radiation exposure and age, no other risk factors have been associated with Hurthle cell neoplasms.

Presentation

Most patients with Hurthle cell neoplasms present with a solitary thyroid nodule. Approximately 80% of these lesions are nonfunctioning and are therefore "cold" on nuclear scans. Approximately 5% to 60% (in most series, 10% to 35%) of Hurthle cell neoplasms are carcinomas. In patients presenting with malignant lesions, 70% to 80% are confined to the gland, 11% have lymph node metastasis, and 15% have distant metastasis, most commonly to bone or lung. Patients may also present with advanced local disease manifested by esophageal or airway obstructive symptoms.

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