The patient went on to have a partial resection. 

Histology

Sections show brain widely infiltrated by a diffuse glioma. The tumor cells have enlarged oval-to-angulated nuclei, with fairly coarse chromatin. They are set within a fibrillar background that also contains plentiful mucin. Mitoses are easily identified. There is no necrosis but focal microvascular proliferation is identified. 

Immunohistochemistry:

• IDH-1 R132H: positive (mutant)
• GFAP: positive
• OLIG2: positive
• ATRX: negative (mutant)
• p53: positive (mutant)
• p16 CDKN2A: positive (not lost) 
• Ki67: 10%

FINAL DIGANOSIS: adult-type astrocytoma, IDH-mutant (CNS WHO grade 4)

Discussion

This case nicely illustrates how even in older individuals IDH-mutant astrocytomas are sometimes encountered, however, their prevalence is highly determined by age.