The patient went on to have a resection. 

Histology

Sections show a focally calcified, 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 1/2ohpf). No necrosis or microvascular proliferation is seen.

IMMUNOHISTOCHEMISTRY:

• GFAP: Negative
• NogoA: Positive
• Nesfin: Positive (intermediate)
• IDH-l R132H: Positive (mutated)
• ATRX: Positive (not mutated)
• p53: Positive p16: Positive
• Topoisomerase labeling index: Approximately 5%

Combined 1p/19q co-deletion detected by FISH

FINAL DIAGNOSIS: Oligodendroglioma (WHO Grade II).