CASE IS OPEN FOR DISCUSSION:  
75 yrs old male with resected mediastinal mass.  
MACRO: Fatty tissue piece of 6x4,5x2 cm. Lobated greyish tumor with defined margins 2,5x2x2 cm with yellowish cyst 1,2x1x0,6 cm. 4 lymph nodes up to 0,5 cm found.  
HISTO: fat tissue with "tumor":  
- Lymphoid stroma with II lymphoid follicles (without TdT+ lymphoblasts) and epithelial proliferation (cysts, strands, serpantines);  
- Cysts with hyalinised walls and papillary epithelial formations;  
- 1 lymphoid nodule within cyst with epithelial diffuse network (block 3).  
- Thymus residual nests with TdT+ cells at periphery and 4 reactive nodes (not included).  
 
PROPOSAL:  
Thymic Hyperplasia With Lymphoepithelial Sialadenitis (LESA)–like Features with multilocular thymic cyst.  
Reactive lymphadenopathy (4).  
 
QUESTION:  
 
Single nodule with diffuse PanCK+ network within cyst avoiding TdT+ lymphobblasts (thymoma B like).  
LITERATURE:  
Weissferdt A, Moran CA. Thymic hyperplasia with lymphoepithelial sialadenitis (LESA)-like features: a clinicopathologic and immunohistochemical study of 4 cases. Am J Clin Pathol. 2012;138(6):816-822.  
 
ThanYouaLot.

tzankov 2020-10-01 18:28	I think it is a type A thymoma with aquired multilocular thymic cyst. All, the thick capsule, the circumscribed nodular appearance, the germinal centers and the paucity of TdT+ cells may fit. Since I am not allowed to look at the digital slides, I can't give more profound opininon.
ugnius 2020-10-02 16:02	Thanx. Encapsulated one let it be as thymoma A. But (lympho)epithelial complexes outside in the back of b follicles practically do not recapitulate thymus structure (?).. Su LESA idea evolved.