Astrocytoma (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: Infiltrative lesion with mass effect involving left mesial temporal structures and extending along the body of the left hippocampus, most likely representing a low-grade glioma. DDx paraneoplastic encephalitis. 

The patient went on to have surgery.

Histology

MICROSCOPIC DESCRIPTION: 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).