Gemistocytic astrocytoma (gliomatosis growth pattern)

There is a large region of subcortical hypodensity within the left temporoparietal region, with sparing of the overlying grey matter. Significant local mass effect and midline shift. No definite enhancing mass lesion on the post contrast study. CTA COW (not shown) is normal. 

There is a large area of abnormal high T2/flair signal involving the cortex and white matter of the left temporal, parietal and occipital lobe, including involvement across the splenium of the corpus callosum and into the left thalamus. No region of abnormal contrast enhancement, elevated cerebral blood volume (CBV) or signal dropout on SWI. MR spectroscopy demonstrates reduced NAA and elevated choline, with small lactate peaks centrally. 

There is a serpiginous area of increased diffusion restriction across the medial aspect of the left temporal lobe, which probably represents the hippocampal body/tail, possibly secondary to seizure activity. 

Conclusion: Large mass involving the left temporal, parietal and occipital lobes without contrast enhancement. Findings are most in keeping with a low-grade infiltrative astrocytoma. 

Histology

The patient went on to have surgery.

MICROSCOPIC DESCRIPTION:

Sections of brain show a moderately cellular tumor composed of moderately pleomorphic cells containing oval, hyperchromatic nuclei with inconspicuous nucleoli and dense eosinophilic cytoplasm. Tumor cells are arranged in diffuse sheets. Occasional mitotic figures are identified (up to 1/10hpf). No necrosis or microvascular proliferation is seen.

• GFAP Positive
• Nogo A Negative
• Nestin Negative
• IDH-1 R132H Positive (mutated)
• ATRX Positive (non-mutated)
• MGMT Positive (likely non-methylated)
• p53 Positive
• p16 Positive
• Topoisomerase labeling index: Approximately 12%

FINAL DIAGNOSIS: IDH-1 mutated gemistocytic astrocytoma (WHO Grade II).