Paraganglioma of the thyroid gland: a rare entity.

Paragangliomas are neuroendocrine tumors. The thyroid gland is one of the anatomic sites in which paraganglia are not normally located and are exceptionally rare. We report a case of a 36-year-old Hispanic woman with a soft mass measuring about 30 mm in the right thyroid lobe. Patient was operated on and the neoplasm showed microscopically a typical nesting organoid pattern (zellballen). The inmunohistochemical analysis revealed that the tumor showed strongly and diffuse stain for NSE, Synaptophysin, Chromogranin A, and S-100 protein in the sustentacular cells, whereas no inmunoreactivity was detected with antibodies against thyroglobulin, calcitonin, TTF-1, CEA, and AE1-AE3. The MIB-1 labeling showed 7% of neoplastic cells. Head and neck paragangliomas usually develop slowly, and this tumor exhibited a low proliferative activity. In view of the uncertain malignant potential of paragangliomas, we recommended a careful long-term follow-up.