Thyroid adenoma with extensive extracellular mucin deposition: report of a case.

A thyroid tumor with extensive extracellular mucin deposition is extremely rare. We herein describe a case of a thyroid adenoma with prominent myxoid stroma. A 63-year-old man presented with a mass in his right anterior neck. Radiological examinations showed this mass to be a thyroid tumor with a cystic component. The histopathological findings showed the stroma of this tumor to consist of abundant myxoid materials which stained gray-bluish for hematoxylin-eosin. The myxoid material was positive for alcian blue, whereas periodic acid-Schiff did not stain this material. No intracytoplasmic mucin was identified. In an immunohistochemical study, the tumor cells were negative for cytokeratin 19. Furthermore, positive staining was observed for thyroglobulin while a negative finding was seen for calcitonin.