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 arrangem
ent. 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. Immunohistochemistr
y demonstrated thyroglobulin positivity in the nonclear neoplastic cells, w
hereas most of the clear cells were negative. Ultrastructural study demonst
rated the gradual transition from protein synthesis to lipid synthesis as t
he neoplastic cells progressed fi om nonclear to clear. The study suggested
that the lipid accumulation resulted from the uncontrolled fatty acid synt
hesis in the neoplastic cells rather than metaplasia. The karyotype of the
tumor cells was normal, 46XX Literature of lipid-rich thyroid neoplasms wer
e reviewed.