Lipid-rich follicular carcinoma of the thyroid in a patient with McCune-Albright syndrome.

A 41-year-old woman with McCune-Albright syndrome and a 2-cm thyroid nodule of ten years' duration presented for fine-needle aspiration, which yielded vacuolated clear cells with granular chromatin in pseudopapillary arrangement. The resected tumor showed 90% clear cells and 10% nonclear cells with capsular and vascular invasion. The cytoplasmic vacuoles in the clear cells were 3+ for oil red O stain in touch imprint cytology. Immunohistochemistry demonstrated thyroglobulin positivity in the nonclear neoplastic cells, whereas most of the clear cells were negative. Ultrastructural study demonstrated the gradual transition from protein synthesis to lipid synthesis as the neoplastic cells progressed from nonclear to clear. The study suggested that the lipid accumulation resulted from the uncontrolled fatty acid synthesis in the neoplastic cells rather than metaplasia. The karyotype of the tumor cells was normal, 46XX. Literature of lipid-rich thyroid neoplasms were reviewed.