Paraganglioma-Like Adenomas of the Thyroid (PLAT): Incidental Lesions with Unusual Features in a Patient with Nodular Goiter.

We discovered two well-demarcated nodules incidentally in a thyroid removed because of a nodular goiter. Histologically, the nodules showed a pattern of paraganglioma or so-called paraganglioma-like adenoma of the thyroid (PLAT), with lobules of polygonal and oval cells in a vascular stroma, but the immunohistochemical markers typical of paraganglioma, including chromogranin, synaptophysin, Leu 7 and 5-100, and thyroglobulin, characteristic of PLAT, were negative in the tumor cells. C-cell markers calcitonin and somatostatin were also negative. Stain for neuron-specific enolase (NSE), however, showed a distinctive pattern of reactivity within cells at the periphery of the lobules, whereas all tumor cells stained positively for keratins. Stain for carcinoembryonic antigen showed a focal interstitial pattern that corresponded to small intercellular spaces filled by microvilli identified ultrastructurally. This pattern of immunohistochemical staining has not been previously described in paraganglioma or in PLAT, and may have implications about the origin and nature of these controversial entities.