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Right frontal lesion has 2 components:a nodular component medially that has herniated beneath the falx to cross midline with multiple small vessels and wispy enhancement, and a crescentic lateral component that demonstrates the T2 FLAIR mismatch sign. There is additional surrounding peritumoural edema. The lesion appears intra-axial and solitary. Local mass effect has compressed the right frontal horn and created a midline shift of 1 cm and has displaced the 2 A2 branches (in close proximity to its left posterior margin)
No significant diffusion restriction. No calcification on CT. No internal hemorrhage.
Solitary right frontal intra-axial lesion is most likely to represent a glioma. The T2 FLAIR mismatch favors a non 1p19q codeleted IDH mutant diffuse astrocytoma while the more medial nodule of wispy enhancement with internal vascularity is suspicious for a high-grade/anaplastic component.
The patient went on to have a resection.
Sections of cerebellar cortex and white matter show a cellular tumor with a loose fibrillary background. Tumor cells have ovoid to angulated hyperchromatic nuclei with some gemistocytic cells. Mitoses are rare with up to 1 per 50 HPF within the most cellular areas. Necrosis and microvascular proliferation are not present.
- GFAP: Positive
- OLIG2: Positive
- IDH-1 R132H: Positive (mutated)
- ATRX: Lost (mutated - implies intact (not deleted) 1p19q status)
- p53: Positive
- p16 CDKN2A: Patchy
- Ki67: Less than 5%
FINAL DIAGNOSIS: diffuse astrocytoma, IDH-mutant (WHO Grade II).
Although the grade histologically is only WHO grade II, the presence of enhancement and lower ADC values are concerning for a higher grade component. Depending on how much of the tumor has been sent to pathology and which parts were examined there is always the risk of under-grading.