Localized Primary Thymic Amyloidosis Presenting as a Mediastinal Mass: A Case Report

ABSTRACT

We herein describe a case of a 55-year-old healthy woman with localized primary thymic amyloidosis presented as a mediastinal mass, found incidentally by chest radiography. Computed tomography revealed a 4.1 cm soft tissue lesion with nodular calcification in the left anterior mediastinum. The resected specimen was a well-defined lobulating mass with calcification. Microscopically, the mass was consisted of amorphous eosinophilc hyalinized substances involving the thymus and intrathymic lymph nodes. These eosinophilic substances showed apple-green bi-refringence under polarized light after staining with Congo red. In immunohistochemical study, they were positive for kappa and lambda light chains and negative for amyloid A. There was no evidence of systemic amyloidosis in clinical investigations. A final diagnosis of localized primary thymic amyloidosis was made.