The patient went on to have a resection.

Histology:

Paraffin sections show small fragments of a moderately cellular tumor. Tumor cells have mildly pleomorphic round and oval nuclei with finely granular chromatin. Nucleoli are conspicuous within larger nuclei of scattered tumor cells. Tumor cells are arranged in diffuse sheets. Cell poor areas with the appearances of neuropil are noted. No mitotic figures are identified. There is no microvascular proliferation and no necrosis is identified.

IMMUNOHISTOCHEMISTRY:

• Synaptophysin: positive
• NeuN: positive
• tubulin: positive
• Neurofilament protein (NFP): positive
• GFAP negative
• topoisomerase proliferation index: ~2%

FINAL DIAGNOSIS: central neurocytoma (WHO Grade II)