#00063761

A 70-year-old female presented with right hemiparesis and altered mental status. Imaging showed a mass within the left thalamus and no lesions identified in parts of the body. (a) The mass biopsy showed diffuse proliferation of medium to large pleomorphic lymphoid cells with round to oval nuclei, some with distinct nucleoli, and scant to moderate amount of cytoplasm infiltrating the brain parenchyma. The abnormal cells were positive for CD2 (b), CD43 (c), CD30 (d), MUM1 (e), BCL-2, P53 (partial); essentially negative for CD4 and had a high Ki-67 (90%). The abnormal cells were negative for CD45 (f), CD3 (g), CD20, CD5 (h), CD7, CD8, CD25, CD56, CD10, CD15, CD34, CD68, CD79a, CD117, ALK-1, TIA-1, Granzyme B, CD138, BCL-1, AE1/AE3, EMA-1, LMP-1, and MPO. T cell receptor gene rearrangements showed monoclonal peak in T-gamma V1-8, V9 (i), V10, V11, T-beta-A, B and C regions. Overall, these findings were most compatible with a primary CNS T cell lymphoma.