Thyroid paraganglioma: a clinicopathologic and immunohistochemical study of three cases.

We report three cases of intrathyroidal paraganglioma. The patients were adult women without significant personal or family histories that presented with an asymptomatic thyroid nodule. The tumors were single, well-circumscribed solid masses, 2 cm in greatest diameter, located within one thyroid lobe. Microscopically, they were encapsulated and showed the typical nesting (Zellballen) pattern of paraganglioma in other sites. Two of the tumors were composed of small- to medium-sized cells with granular amphophilic cytoplasm, and the third consisted of relatively large cells having a similar staining quality. Immunohistochemically, all tumors showed positivity for neuron-specific enolase, chromogranin A, and synaptophysin. S-100 protein-positive sustentacular cells were demonstrated in each case. Negative staining for epithelial markers, thyroglobulin, carcinoembryonic antigen, calcitonin, calcitonin gene-related peptide, serotonin, vimentin, and Congo red excluded other tumors that were considered in the differential diagnosis, such as medullary carcinoma, hyalinizing trabecular adenoma, atypical follicular adenoma, Hurthle-cell neoplasm, and metastatic carcinoid tumor. The patients were alive and well without evidence of recurrent disease at the time of the last follow-up. The previous literature on these tumors is discussed. We conclude that intrathyroidal paraganglioma exists and that this tumor can be distinguished from other similar-appearing neoplasms in this organ.