The tumor is a rare presentation of Gliosarcoma with a primitive neuronal component. Gliosarcomas arise from sarcomatous transformation of glioblastomas, whereas primitive neuronal cells typically present as solid nodules of neuronal differentiation within a background of a diffuse glioma. In both variants, expression of GFAP can be lost, although scattered positive tumor cells (as in this case) can be very helpful in identifying a glial origin. Palisading necrosis and microvascular proliferation were present in this case. Fluorescence in situ hybridization also showed polysomy 7 and monosomy 10, a classic finding seen in IDH-wildtype glioblastomas,  within both the gliosarcomatous and primitive neuronal areas. 

The sarcomatous component in gliosarcomas can be variable, with a reticulin stain being great for highlighting fascicular architecture when there is spindle cell histology. Macroscopically, gliosarcomas may appear well-circumscribed and be mistaken for metastases or meningiomas. They have similar treatment and prognosis as glioblastomas.

Primitive neuronal differentiation is usually characterized by synaptophysin expression, marked elevations in Ki67 and p53 immunoreactivity, and MYC or MYCN amplification (~40% of cases). CSF dissemination is common in these tumors and should prompt spinal MRI  to evaluate for drop metastasis.