The patient went on to have a craniotomy and biopsy. 

Histology

The sections show features of a moderately cellular glial tumor. There is a proliferation of predominantly neoplastic astrocytes. They are of mostly fibrillary type with smaller amounts of protoplasmic astrocytes. The former cells have elongated, angulated and hyperchromatic nuclei and much rounder nuclei in the latter cells.

A minor population of neoplastic oligodendroglial cells is also present (less than 10%). These cells have round nuclei and perinuclear haloes. They extend into the cortex with secondary structuring. Scattered mitoses are seen but there are less than 5 per 10 high-power fields. No microvascular proliferation or necrosis is present. The features are those of oligoastrocytoma. The tumor cells are IDH-1 positive. The Ki-67 index is about 10%. They are p53 and MGMT negative. The neoplastic astrocytes are ATRX negative.

FINAL  DIAGNOSIS:

Oligoastrocytoma (NOS) NOS (WHO Grade II).

NOTE: This case predates the 2016 WHO classification of CNS tumor revision. As no 1p19q co-deletion status is available a formal diagnosis cannot be reached and the NOS is therefore used (not otherwise specified) - which is recognized in the current classification for cases where molecular information is unavailable.