PMC8794278_01
Thymic amyloidosis (Case 1). (A) Chest CT showed a solid, large mass with calcification located in the anterior mediastinum in the mediastinal window. (B) A hard tumor with a smooth surface originated from the thymus gland and firmly adhered to the pericardium alone (arrowheads). The left innominate vein was encircled using vessel tape. (C) The resected tumor measured 100 mm in maximum diameter, had a smooth appearance, and was extremely firm. The cut surface was light yellow with cystic lesions. (D) The tumor included diffuse deposits of amorphous and eosinophilic material, calcification, lymphocytes and plasma cells, but no neoplastic cells (hematoxylin and eosin stain). (E) Amorphous materials were positive in direct fast scarlet 4BS staining and showed an "apple-green" birefringence under polarized light (arrows). (F) Immunohistochemical staining was positive for kappa light chain.
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In case 1, chest CT showed a solid, large, soft tissue density mass with calcification located in the anterior mediastinum (Figure 1A), and a grand glass opacity (GGO) lesion in the right upper lobe and multiple lung cysts in bilateral lung fields. The anterior mediastinum tumor was found to originate from the thymus gland and to be adhered to the pericardium firmly, but could be peeled off manually (Figure 1B). The cut surface was light-yellow with cystic lesions (Figure 1C). Histologically, small calcification foci and a small number of lymphocytes and plasma cells were observed in diffuse deposits of amorphous and eosinophilic material (Figure 1D). These findings were compatible with amyloidosis (Figure 1E). Subsequent immunohistochemical staining showed that the amyloid material was positive for kappa light chain (Figure 1F), slightly positive for transthyretin (TTR), and negative for lambda light chain, amyloid A protein.
Thymic MALT lymphoma with amyloid deposition (Case 2). (A) A large mass consisting of a cystic lesion and a solid portion was located on the right side of the heart toward the anterior mediastinum in the mediastinal window on chest CT. Small calcification was also recognized. (B) Intraoperative findings. The tumor was well capsulated. Adhesion to and invasion of surrounding organs were not seen. (C) The maximum diameter was 120 mm and the tumor had a smooth surface appearance. On sectioning, the tumor appeared to be solid yellowish, and was circumscribed by a thin fibrous capsule with occasional small cysts containing clear yellowish fluid. (D) The tumor consisted of diffuse monotonous proliferation of mononuclear cells, which occasionally infiltrated into Hassall bodies forming a LEL (hematoxylin and eosin stain). (E) An immunohistochemical examination for cytokeratin AE1/AE3 outlined Hassall bodies and confirmed formation of a LEL. (F) Focal deposits of amorphous and eosinophilic materials were scattered, and were positive in DFS 4BS staining and gave an "apple-green" birefringence under polarized light. LEL, lymphoepithelial lesion.
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In case 2, chest CT showed a large mass with a cystic lesion located on the right side of the heart toward the anterior mediastinum (Figure 2A) and multiple cysts in both lungs. In the operation, the tumor was found not to have invaded the surrounding structures and was easily removed (Figure 2B). On sectioning, the tumor was solid yellowish, and was circumscribed by a thin fibrous capsule with small cysts containing clear yellowish fluid (Figure 2C). The mononuclear cells occasionally infiltrated into Hassall bodies to form lymphoepithelial lesions (LELs) (Figure 2D,E). The deposits were positive on DFS 4BS staining and showed an "apple-green" birefringence under polarized light, suggesting amyloidosis (Figure 2F).