The thyroid gland is a relatively uncommon site for a secondary malignancy; even less common is a case of malignant melanoma metastatic to the thyroid. We describe the case of a 68-year-old man who presented with a neck mass in the posterior triangle. Fine-needle aspiration biopsy (FNAB) identified the mass as a malignant melanoma. The patient had had no known primary skin melanoma. He underwent a left modified radical neck dissection, and the mass was discovered to be a positive lymph node. Postoperatively, he declined to undergo radio- and chemotherapy. Eighteen months later, he returned with a diffusely enlarged thyroid. FNAB again attributed the enlargement to malignant melanoma. Soon thereafter, the patient began experiencing seizures, and on magnetic resonance imaging, he was found to have metastatic disease to the brain. He developed ventilator-dependent respiratory failure and required a subtotal thyroidectomy for the placement of a tracheostomy tube. Patients who present with a thyroid nodule and who have a history of malignancy present a diagnostic dilemma: Is the nodule benign, a new primary, or a distant metastasis? The findings of this case and a review of the literature strengthen the argument that any patient with a thyroid mass and a history of malignancy should be considered to have a metastasis until proven otherwise.
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