Hurthle cell adenoma of the mediastinum: Intraoperative cytology and differential diagnosis with correlative gross, histology, and ancillary studies

A 66-year-old man was found to have a 7.5 cm mediastinal mass detected on r outine chest X-rays as part of his preoperative work up for an inguinal her nia repair. An orthotopic (normally located) nongoitrous thyroid gland with out evidence of connection to the mediastinal mass was also identified. The clinical differential diagnoses included lymphoma, thymoma, and germ cell tumor. fine-needle aspiration (FNA) biopsy smears and touch imprints of the mediastinal mass showed a loosely cohesive, highly cellular population of relatively uniform cells with abundant granular cytoplasm, low nuclear to c ytoplasmic (N/C) ratios, and prominent nucleoli consistent with a Hurthle c ell (HC) neoplasm. Subsequently, the diagnosis of HC adenoma was confirmed on the surgically excised mediastinal mass. To the best of our knowledge, t he surgical pathology and cytologic features of an HC adenoma of the medias tinum have not been reported in the literature. The gross, histologic, immu nohistochemical, and electron microscopic (EM) findings, in addition to the cytologic features, are presented along with a differential diagnosis of t his mediastinal neoplasm. Diagn. Cytopathol. 2000;22:16-20. (C) 2000 Wiley- Liss, Inc.