Lipid-rich adenoma of the thyroid.

A case of clear cell adenoma of the thyroid associated with an anaplastic spindle cell carcinoma is reported. Histochemical and ultrastructural examination showed abundant cytoplasmic lipid inclusions and frequent cytoplasmic vesicles, which both may have contributed to the clear cell change. The follicular cell origin was demonstrated by thyroglobulin positivity using immunohistochemistry. We believe that this adenomatous lesion shows close similarities with the lipid-rich cell adenoma first described by Schröder et al. in 1984.