Presentation
Severe headache - suspected subarachnoid hemorrhage.
Patient Data
No evidence of intracranial bleed.
Left temporal intra-axial cystic mass abutting the left ventricle, partially surrounded by mild edema. Post-contrast mild parenchymal enhancement at the anteroinferior edge of the mass, representing a solid component. The lesion compresses the hippocampus and the parahippocampal gyrus, the midbrain, and the upper part of the pons, and causes subfalcine herniation of up to 5 mm and mild right ventricular hydrocephalus.
In summary: left temporal mass with large cystic component, most compatible with high-grade astrocytoma.
The patient was transferred to another institution for eventual neurosurgery, where she first underwent MRI brain (study not available) on the same day as the CT head.
MRI report
Left temporal intra-axial cystic lesion with a solid enhancing component and mild perilesional edema. The lesion compresses the temporal horn of the left ventricle and bulges into the ventricle. Highly suspicious for high-grade glioma.
Enhancing extra-axial lesion on the floor of the right middle fossa, involving Meckel's cave and right cavernous sinus, and entering the foramen ovale. No narrowing of ipsilateral cavernous carotid. Differential diagnosis includes meningioma, granulomatous lesion, IgG4-related mass, lymphoproliferative process.
A small hyperintense lesion in the body of the left ventricle, with no diffusion restriction of enhancement. Its nature is not clear, possibly subependymoma.
Case Discussion
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.