Malignant teratoma of the thyroid: A difficult diagnosis by fine-needle aspiration.

Primary thyroid teratomas are rare, usually benign, and typically occur in children. We report the unusual occurrence of a malignant thyroid teratoma in a young man. Initial ultrasound and CT studies revealed an 8.5 heterogeneous mass involving the entire right thyroid lobe causing tracheal compression and deviation. Fine-needle aspiration (FNA) revealed malignant cells with possible neuroendocrine features. Similar findings have been previously reported, with an occasional interpretation as possible medullary thyroid carcinoma. In no report, as with our case, has the correct diagnosis been suggested with FNA. The surgical specimen contained abundant primitive neuroepithelium with a very minor component of mature ectodermal tissue in one area. Like this case, an abundance of immature neuroepithelium has been reported in essentially all previous reports of primary malignant thyroid teratoma, sometimes creating a challenge to find another type of germ cell tissue. Array comparative genomic hybridization studies in this case revealed a markedly complex karyotype including gain of chromosome 12 and loss of 17p. Amplification of MYCN, EWSR1 rearrangement and isochromosome 12p were not identified, providing no evidence for neuroblastoma or Ewing sarcoma/peripheral neuroectodermal tumor, both of which have also rarely been reported as primary thyroid tumors. With the use of cisplatinum-based chemotherapy combined with radiation, survival times have increased dramatically. Our patient is now disease free and back to his normal activities after relatively short follow-up. Although rare, it is important to be aware that teratomas may present as a thyroid nodule. Recognition by FNA is challenging, and requires multiple modalities for full identification.