Glioblastoma IDH-wildtype (mesial temporal)

An area of high signal on FLAIR within the left mesial temporal structures and extending along the body of the left hippocampus has positive mass effect. No contrast enhancement or elevated cerebral blood volume (CBV) is identified. Spectroscopy suggests decreased NAA and increased myoinositol. Right-sided mesial temporal structures are normal. Minor periventricular and subcortical white matter disease. No acute diffusion changes.

Conclusion:

An infiltrative lesion with mass effect involving left mesial temporal structures and extending along the body of the left hippocampus, most likely representing a diffuse glioma.

The differential diagnosis in paraneoplastic encephalitis. 

The patient went on to have surgery.

Histology

Paraffin sections show fragments of a moderately hypercellular glial tumor involving cortex and white matter. Tumor cells have predominantly fibrillary astrocytic morphology with moderate nuclear and cellular pleomorphism. An occasional mitotic figure is identified. There is no microvascular proliferation and no necrosis is identified. A background population of morphologically unremarkable neurons is noted. No bi-nucleate forms are identified.

IMMUNOHISTOCHEMISTRY:

• GFAP positive

• Nestin negative

• Nogo A positive in native oligodendrocytes

• IDH-1 R132H negative (not mutated)

• ATRX positive (not mutated)

• MGMT negative (likely methylated)

• p53 negative

• p16 CDKN2A positive

• Topoisomerase labeling index: Approximately 5%.

Final diagnosis

IDH-1 R132H wild-type diffuse astrocytoma (WHO Grade II).

Note

This case predates the 2021 WHO classification of CNS tumors; you can tell by the use of Roman numerals to indicate grade. The patient is over 55 years of age and thus sequencing to identify non-R132H IDH mutations is not mandatory as the likelihood of identifying one is very low. Thus, using the current classification this would be considered a molecular glioblastoma despite the low histological grade.