Neuroendocrine tumors of the thyroid gland.

The neuroendocrine lesions of the thyroid are few in number and include C-cell lesions (C-cell hyperplasia and medullary carcinoma), mixed C-cell and follicular-derived tumors, paraganglioma, intrathyroidal parathyroid adenoma, and metastasis to the thyroid from neuroendocrine carcinoma arising elsewhere. However, some follicular-derived lesions of the thyroid can show trabecular and nesting growth patterns characteristic of neuroendocrine tumors. These lesions should also be included in the differential diagnosis of primary and secondary neuroendocrine tumors of the thyroid.