The patient went on to have surgery. 

Histology

MICROSCOPIC DESCRIPTION:

Sections show a moderately cellular tumor composed of moderately pleomorphic cells containing rounded, hyperchromatic nuclei with inconspicuous nucleoli and focal perinuclear clearing. Tumor cells are arranged in diffuse sheets.  Focal microcystic change and secondary structuring are observed.  No mitotic figures are identified.  No necrosis or microvascular proliferation is seen.

IMMUNOHISTOCHEMISTRY:

• GFAP: Positive
• Nogo A: Positive
• Nestin: Positive (low)
• IDH-1 R132H: Positive (mutated)
• ATRX: Positive (non-mutated)
• MGMT: Negative (likely methylated)
• p53: Equivocal
• p16: Positive

Topoisomerase labeling index: Approximately 5%.

FISH for chromosome 1p/19q deletion:

• Chromosome 1.
  • Mean copies 1p per cell:      1.12
  • Mean copies 1q per cell:      1.6
  • 1p/1q ratio:                  0.70
  • Interpretation:               1p loss detected by FISH
• Chromosome 19.
  • Mean copies 19q per cell:     1.13
  • Mean copies 19p per cell:     1.73
  • 19q/19p ratio:                0.65
  • Interpretation:               19q loss detected by FISH

SUMMARY:  Chromosome 1p/19q co-deletion detected by FISH

FINAL DIAGNOSIS:

Oligodendroglioma (IDH mutated, chromosome 1p/19q co-deleted) - WHO Grade II.