Hyalinizing trabecular adenoma of the thyroid gland: recognition and characterization of its cytoplasmic yellow body.

Many round, pale yellow, cytoplasmic inclusion bodies were found in hematoxylin and eosin-stained sections of a hyalinizing trabecular adenoma of the thyroid. The bodies were refractile and frequently had a microvacuolated or granular substructure. They were usually located close to the nucleus, often indented it, and rarely occurred within it. Histochemically, they showed a glycosaminoglycan, proteoglycan, and lipid content, displayed autofluorescence on exposure to ultraviolet light, and were unreactive with a variety of immunostains. Ultrastructurally, the inclusions were consistent with giant lysosomes, showing parallel whorled and arrayed membranes ("fingerprint" bodies) as a component of their substructure. Review of sections of 75 hyalinizing trabecular adenomas in our files revealed that the cytoplasmic bodies were present in all cases (100%), indicating that these inclusions most likely are a universal feature of the neoplasm.