The patient went on to have a lLeft temporal craniotomy and debulking of the tumor.

Histology

Immunohistochemistry: The immunostains with the antibody anti-GFAP, Vimentin, and Olig2 are diffusely positive. ATRX is retained. P53 is negative. Ki67 is about 20%. IDH1 is negative.

​Diagnosis: Anaplastic oligodendroglioma (WHO grade III), IDH1 wild type.

Note: This case did not establish an IDH mutation nor does it include 1p19q co-deletion status (both of which are required for complete diagnosis by the updated 4th edition (2016) and 5th edition (2021) WHO classification of CNS tumors) although retained ATRX suggests 1p 19q deletion. It is, therefore, possible that this tumor harbors a non-IDH-1 R132H mutation, but without documentation, this tumor should be classified as an oligodendroglioma not otherwise specified (NOS) grade 3.