Yolk sac tumor of the thyroid gland: a case report.

Extragonadal yolk sac tumors are uncommon and usually seen in sacrococcygeal, mediastinal, intracranial, and retroperitoneal sites. Yolk sac tumors of the head and neck region are rare, and the few reported cases have arisen in neonates or infants in conjunction with a teratoma or other germ cell tumor subtypes. We report a unique case of a pure yolk sac tumor presenting as a primary lesion in the right thyroid lobe of a 10-year-old girl. The diagnosis was suspected after fine-needle aspiration, and extensive sampling of the thyroidectomy specimen revealed no teratoma or other germ cell tumor. Serum α-fetoprotein levels were markedly elevated 6 days after excision, and imaging disclosed numerous bilateral pulmonary nodules suggestive of metastatic disease but did not reveal a mediastinal mass. The tumor has shown a favorable response to bleomycin, etoposide, and cisplatin chemotherapy. To the best of our knowledge, this is the 1st description of a primary pure yolk sac tumor of the thyroid.