Fig. 2

(A). Grossly, the anterior mediastinal mass resembled an enlarged thymus gland; (B). the cut surfaces were gray-white in color and medium in texture, showing multinodular architecture and focal cystic changes; (C). on the low magnification (H&E, ×20), predominantly nodular or lobulated solid structures separated by fibrous and adipose tissue; (D). focal cystic structures (H&E, ×20); (E). on the higher magnification, the lobulated solid structures were characterized by prominent lymphoid follicles containing germinal centers and florid hyperplasia of thymic epithelial cells (H&E, ×40); (F). proliferation of dilated Hassall bodies (H&E, ×100); (G). cholesterol clefts (H&E, ×100); (H). lymphoepithelial lesions (H&E, ×200); (I). CD3 + T cells scattered in the interfollicular areas (EnVision, ×100); (J). CD20 + B cells mainly populated in lymphoid follicles (EnVision, ×100). (K). pan-cytokeratin staining showed reticular hyperplasia of thymic epithelial cells (EnVision, ×100); (L). TDT + immature T cells were almost completely absent (EnVision, ×100)