Hurthle cell carcinoma is rare, but usually, an aggressive tumor of the thyroid gland, as it possesses a rather high rate of metastatic spread compared to other thyroid malignancies. Dysphagia, dyspnea, voice changes and an apparent mass in the neck are main findings. The initial diagnosis can be made through a thorough clinical exam, ultrasonography, and a fine-needle aspiration biopsy, but a histological exam showing > 75% of hurthle cells is necessary in order to confirm this malignancy.
Hurthle cells (large, polygonal and well-demarcated cells containing a granular cytoplasm, a large hyperchromatic nucleus, and a prominent nucleolus) are considered to be a rather common finding on histological samples of thyroid nodules, which are present in up to 8% of the population . Many different disorders of the thyroid gland have been associated with the appearance of hurthle cells, including chronic lymphocytic thyroiditis (CLT), Graves' disease, and multinodular goiter, but also a range of benign and malignant neoplasms   . Hurthle cell carcinoma accounts for < 5% of all differentiated thyroid tumors and is suspected when the biopsy specimen contains > 75% of hurthle cells, with the absence of a complete lesional capsule     . Hurthle cell carcinoma must be included in the differential diagnosis when patients present with a hard and immobile mass that may be accompanied by dysphagia, voice changes, or even dyspnea , the reason being mechanical compression of the esophagus and/or the trachea. Unfortunately, hurthle cell carcinoma is known for its potentially aggressive clinical course with a higher rate of metastatic spread when compared with other malignancies of the thyroid gland, and in addition to male gender and increased age, both being established as poor prognostic factors, the size of the tumor is important in determining the survival rates .
An early diagnosis of hurthle cell carcinoma may significantly improve patient outcomes, which is why physicians must obtain a detailed patient history and conduct a thorough physical examination . The presence of previously mentioned symptoms of dysphagia/dyspnea and detection of a palpable mass in the neck mandates a more advanced workup. Ultrasonography of the neck is a valuable initial tool in the assessment of thyroid masses (and examination of proximal lymph node spread), but because both hypoechoic and hyperechoic (and sometimes isoechoic) appearance of hurthle cell carcinoma has been observed (as well as marked variations in vascularity of the tumor) , the use of fine-needle aspiration biopsy (FNAB) is imperative    . When an abundance of hurthle cells is observed in biopsy samples (>75%), a lesion of > 4 cm is highly suggestive of a hurthle cell carcinoma , in which case additional imaging studies, such as computed tomography (CT) and magnetic resonance imaging (MRI) are recommended for assessing potential spread to the adjacent structures in the neck and distal organs . To solidify the diagnosis, a histological examination must show capsular and/or vascular invasion of the tumor  .