Diffuse astrocytoma IDH mutant
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A high T2 signal mass in the posterior part of the left superior frontal gyrus, abutting and involving the precentral gyrus has low T1 signal and partial FLAIR suppression and peripheral restricted diffusion. No enhancement or increased perfusion. Spectroscopy demonstrates elevated choline and reduced NAA. No abnormal meningeal enhancement identified. The dural venous sinuses are patent.
Conclusion: The overall appearances of the medial posterior left frontal lobe mass would most favour a low-grade astrocytoma (previously classified as a protoplasmic astrocytoma).
The patient went on to have surgery.
Sections show a moderately cellular tumour composed of moderately pleomorphic cells containing round to oval, hyperchromatic, vesicular nuclei with inconspicuous nucleoli. Tumour cells are arranged in diffuse sheets with a "protoplasmic" morphology. No mitotic figures are identified. No necrosis or microvascular proliferation are seen.
- GFAP Positive
- Nogo A Positive
- Nestin Positive (intermediate)
- IDH-1 R132H Positive (mutated)
- ATRX Equivocal
- MGMT Negative (likely methylated)
- p53 Equivocal
- p16 Negative
- Topoisomerase labelling index: Approximately 1-2%.
FISH For Chromosome 1p/19q Deletion: No 1p/19q loss detected.
FINAL DIAGNOSIS: Diffuse astrocytoma, IDH-1 mutant (WHO Grade II).
This case is typical of the entity previously known as protoplasmic astrocytoma, which is no longer recognised as a distinct entity in the current (2016) WHO classification of CNS tumours. This is a shame as it is a recognizable tumour and is probably highly predictive of intact 1p19q status.