The patient went on to have a biopsy.

Histology

Sections show cores of brain tissue containing a moderately cellular glial tumor. The tumor cells have enlarged, angulated, moderately pleomorphic nuclei, and are set in a fibrillary background. There are no areas of oligodendroglial morphology.  There is perineuronal satellitosis.  Mitoses are not identified.  There is no microvascular proliferation or necrosis.

IMMUNOHISTOCHEMISTRY

• GFAP:  positive
• IDH1 R132H: positive (mutated)
• ATRX: positive (not mutated)
• p53: negative
• p16: negative
• Ki67: 1-2%

NEXT-GENERATION SEQUENCING GLIOMA GENE PANEL RESULTS:

• 1p/19q codeletion: DETECTED
• EGFR amplification: Not detected
• IDH1 codon 132: PATHOGENIC VARIANT DETECTED (R132H)
• IDH2 codon 172: No pathogenic variant detected
• BRAF codon 600: No pathogenic variant detected
• H3F3A codons 27 and 34: No pathogenic variant detected
• TERT promoter Chr 5: 1295228 (C228T) and chr5:1295250 (C250T): PATHOGENIC VARIANT DETECTED (C228T)

FINAL INTEGRATED DIAGNOSIS: Oligodendroglioma, IDH-mutant and 1p/19q-codeleted (WHO grade II).