[Clear cell carcinoma of the thyroid; diagnostic difficulties]

Thyroid carcinomas with clear cell change are rare neoplasms, and always bring up the possibility of a metastasis from another primary clear cell carcinoma. We report the case of a 33-year-old woman operated on for a solitary cold thyroid nodule. Histologic and ultrastructural studies showed a clear cell carcinoma with a trabecular and follicular pattern. Neoplastic cells included lipid droplets, glycogen granules and intranuclear cytoplasmic inclusions, and were stained with one of the two antithyroglobulin polyclonal antibodies used. Radiologic investigations then showed a tumor mass of the right kidney. Surgical management proved it to be a benign cyst, and assessed the absence of kidney neoplasm. Thus, this case exemplifies the pitfalls in the diagnosis of clear cell thyroid neoplasms, and points out the fact that immunohistochemical staining for thyroglobulin should be systematically performed.