The patient went on to have a resection. 

Histology

Sections show a variably cellular tumor with a prominent microcystic architecture. Tumor cells
demonstrate elongated oval nuclei with inconspicuous nucleoli set within a fibrillary stroma. Frequent Rosenthal fibers and eosinophilic granular bodies are seen. There are focal aggregates of thin-walled, hyalinised blood vessels with the adjacent parenchyma containing hemosiderin deposition. No mitoses, necrosis or microvascular proliferation are identified.

IMMUNOHISTOCHEMISTRY RESULTS:

• GFAP: Positive
• IDH-l R132H: Negative (non-mutated)
• ATRX: Positive (non-mutated)
• p53: Positive
• BRAF V60oE: Negative
• Topoisomerase labeling index: Approximately 1-2%.

FINAL DIAGNOSIS: Pilocytic astrocytoma (WHO Grade I).