The patient went on to have a resection. 

Histology

MICROSCOPIC DESCRIPTION:

​Paraffin sections show a mild to moderately hypercellular tumor with some normal cortex included in the biopsy. The tumor comprises haphazardly arranged atypical astrocytes with mildly pleomorphic and hyperchromatic nuclei. Many astrocytes show bipolar cytoplasmic processes. There is a background of loose myxoid stroma. Scattered neurons are seen within the tumor. They show mild architectural disarray and loss of orientation. Small numbers of scattered lymphocytes are seen dispersed within the tumor as well as cuffing some of the capillaries. Few eosinophilic granular bodies are identfied. There are no rosenthal fibers. No mitotic figures are identified. There is no endothelial cell hyperplasia or necrosis.

The astrocytic component shows strong and diffuse staining for GFAP. The ganglion cells are highlighted with Neu-N. There is no staining by the tumor cells for IDH-1. The Ki-67 proliferative index is 2-3%. The features are those of a low grade glioneuronal tumor with features favoring a ganglioglioma. 

It is difficult to accurately grade this tumor. However, the astrocytic component is dominant and has features of WHO Grade II astrocytoma.

DIAGNOSIS:

Left occipital lesion: Low grade glioneuronal tumor with features favoring ganglioglioma.