A case of Metastatic thymic neoplasm

Additional relevant investigations and comment.
This tumor was from a patient with known history of thymoma type AB (stage pT3; with resection margin margins involved,
lymphovascular invasion, and capsular invasion). The cerebellar mass was sent in consultation to rule out a CNS primary.
Comparison to primary lung tumor and immunohistochemistry (Low molecular weight cytokeratin positive; CK7 focally positive;
CK20 negative; PAX 8 positive; Synaptophysin negative; CD20 scant; STAT6 negative; INI1 retained). The discussion will be
around the overlap in morphologic features of metastatic thymoma and primary brain tumors, diagnostic pitfalls and pearls.

References 
Ahn JY, et al. Thymic carcinoma with brain metastasis mimicking meningioma. J Neurooncol. 2002 Jul;58(3):193-9.
Gharwan H, et al. Thymic epithelial tumors and metastasis to the brain: a case series and systematic review. Transl Lung
Cancer Res. 2017 Oct;6(5):588-599.
Vladislav T, et al. Extrathoracic metastases of thymic origin: a review of 35 cases. Mod Pathol. 2012 Mar;25(3):370-7.