The patient went on to have a resection.

Histology

Sections show a hypercellular tumor composed of moderately pleomorphic cells containing round to oval, hyperchromatic, vesicular nuclei with conspicuous nucleoli and prominent perinuclear clearing. Tumor cells are arranged in diffuse sheets intersected by thin-walled "chicken-wire" capillaries. Occasional mitotic figures are identified (up to 2/10hpf). Tumor cells demonstrate prominent secondary structuring. No necrosis or microvascular proliferation is seen.

IMMUNOHISTOCHEMISTRY:

• GFAP: Positive
• NogoA: Positive
• Nestin: Positive (low)
• IDH-1 R132H: Positive (mutated)
• ATRX: Positive (non-mutated)
• p53: Negative
• p16: Positive
• Topoisomerase labeling index: 8%

FISH RESULTS:

• Chromosome 1 Mean copies 1p per cell: 1.18 Mean copies 1q per cell: 1.95 1p/1q ratio: 0.61
• Chromosome 19 Mean copies 19q per cell: 1.47 Mean copies 19p per cell: 2.48 (polysomy present) 19q/19p ratio: 0.59

FISH summary: 1p/19q co-deletion detected. 

FINAL DIAGNOSIS: Oligodendroglioma, IDH mutant, chromosome 1p/19q co-deleted (WHO Grade II).