Clear cell follicular adenoma of the thyroid: a case report.

A case of clear cell follicular adenoma of the thyroid is presented. The patient presented with a single, hyperactive nodule in the right lobe. The cytologic features include cellular smears with numerous disrupted cells and a granular background. The cytoplasm was abundant, pale grayblue vacuolated or granulated, but not clear. Thyreoglobulin was demonstrated both histologically and ultrastructurally, confirming the follicular-cell derivation of the tumor. Ultrastructurally, the cytoplasm was filled with empty, membrane bound vacuoles. The clear cell change might represent an artifact of formalin fixation and/or the paraffin embedding procedure.