The mass was excised the very next morning.

Pathology report

The mass is composed of medium-sized cells with large nuclei, part of the cells with extensive eosinophilic cytoplasm. The cells create solid surfaces, and in certain areas, there is perivascular organization of cells. Striking cytological atypia and high mitotic activity (14 mitoses/10 HPF counted). Atypical mitoses seen. Suspicion of focal necrosis. No unequivocal microvascular proliferation.

On immunohistochemical staining, the tumor cells stained positive for GFAP, S100, EGFR, and VIM; negative for olig2, IDH1, H3K27M, PAN-KER ,KER18 ,KER8 ,EMA ,NEU-N ,NF, NSE ,SYN ,CD34 ,H3.3G34R/V, and TTF1. Stains for ATRX, BRG1, INI1, and H3K27me3 were positive (preserved). Staining for p53 - very few cells stained positive. On staining for Ki67, there was an average proliferative index of ~30-40%. On staining for reticulin, no significant reticulin fibers were seen in the tumor.

The immunohistochemical results do not support the presence of high microsatellite instability (MSI-H) in the tumor.

Discussion:

The morphological and immunohistochemical findings, as well as the NGS (next-generation sequencing) results, are compatible with high-grade diffuse astrocytic tumor. The fact that it is IDH-wildtype means that, under the current (2021, 5th Edition) WHO classification of CNS tumors it is almost certainly a glioblastoma, particularly as imaging and histology both suggest necrosis. 

This case stresses the need for heightened awareness for intracranial cystic-appearing high-grade tumors: when encountering an intra-axial cystic lesion, always search for a solid component; in this case, hidden in the temporal pole beneath the large cyst and appearing compressed by it.