Amyloid tumor in the anterior mediastinum: report of a case.

A 33-year-old woman being treated for rheumatoid arthritis was referred to our hospital for investigation of a mediastinal mass. A chest computed tomography scan showed an anterior mediastinal mass, 8.5 x 7.0 cm in size, with a cystic lesion and calcification. These findings were suggestive of either a noninvasive thymoma or a mature teratoma. Therefore, we performed tumor resection and thymectomy. Histologically, the tumor consisted of diffuse deposits of massive eosinophilic amorphous material. The tumor was stained red-orange by Congo red, and the staining disappeared following potassium permanganate digestion. Based on these findings, a diagnosis of reactive amyloidosis of the amyloid A-protein-derived type was made. Amyloidosis in the mediastinum has rarely been described.