Thyroid Paraganglioma: "Naked" Nuclei as a Clue to Diagnosis on Imprint Cytology

A cytologic diagnosis of paraganglioma of the thyroid is difficult to make because the thyroid gland is an unusual location for such a tumor and the cytologic findings overlap with other benign and malignant thyroid tumors. We report the case of a 28-year-old female presenting with a solitary mass of the right thyroid gland. A diagnosis of paraganglioma was made on the resected specimen. At the time of tumor resection, imprint cytology was performed. The imprint was hypercellular with cohesive sheets of round cells showing anisokaryosis and anisocytosis. Moreover, there was a second cell type consisting of oval nuclei with dispersed nuclear chromatin present within the sheets and separate as "naked" nuclei. By immunohistochemistry, the cohesive round cells were positive for chromogranin A, indicating chief cells. The naked nuclei were positive for S-100 protein, indicating sustentacular cells. To the best our knowledge, this is the first case report describing naked nuclei as a cytologic feature of paraganglioma. Identification of sustentacular cells provides a clue for the cytologic diagnosis of paraganglioma.