54 yo female patient, clinical myastenia gravis for one year, thymoma found on CT. Treatment with Prednisone and Azathioprine with insufficient improvement, but thymic mass decreased.  
Surgical removal was performed, the mass (about 25 x 15 mm) was extirpated completely, no surrounding infiltration was observed intraoperatively.  
No other involved sites, normal blood counts.  
 
Lobular structure and thymic tissue is partly preserved, including medullary zones (well seen on Ki67, TdT, CD1a and CD5 stainings). Cortical zones are markedly hyperplastic and consist of young blast-looking T-cells with cortical phenotype CD1a+/CD10+/TdT+/CD99+, CD4 weak to intermediate, CD8 mostly negative, CD5 weak, CD45 weak, Ki67 very high (particularly considering the treatment).  
A lot of histiocytes (some fields look like starry sky), a lot of epithelial component, few B-cells.  
 
Is that a B2 thymoma? I am rather afraid to overlook T-lymphoblastic lymphoma here.  
 
Thank you in advance.

tzankov 2017-04-25 20:19

for sure a thymoma of the b-type. yet, because of the treatment given, there is no reliable way to decide whether this is a b2 or a b1 thymoma. since I do not see a lot of Hassall's corpuscles and I see some privascular spaces as well as no thick capsule, I would favor b2.   by the way, myasthenia is not a symptom of t-lbl. in cases that are not clear cut, cytokeratin stainings incl. p63 (the basic network of epithelial cells will be Herby figured out) supported by cd34, lmo2 and notch (+in lbl) may clarify almost all instances.

SergeyN 2017-04-25 21:09

Dear Alex,   Thank you very much! You've really helped a lot lately.