Spinal metastasis of a thyroglobulin-rich Hurthle cell carcinoma detected by fine needle aspiration. Light and electron microscopic study of an unusual case

A prospective diagnosis of metastatic thyroid carcinoma was made on an aspirate of a spinal mass. While the cellular component of the aspirate was compatible with a renal or hepatic neoplasm, the recognition of colloid on air-dried smears defined the cells as Hurthle cells. Biopsy of the spinal tumor and subsequent thyroidectomy revealed a Hurthle cell carcinoma. Whereas the primary tumor showed typical Hurthle cell architecture, with solid tumor nests and microfollicle formation, the metastasis contained areas of macrofollicle formation with abundant colloid production and strong immunocytochemical reactivity for thyroglobulin. This change of histologic pattern from the primary tumor to the metastasis has not been previously reported in Hurthle cell lesions. The unusual light microscopic and ultrastructural aspects of this tumor are discussed.