High-grade astrocytoma with piloid features

High-grade astrocytoma with piloid features is a rare glial tumor which often requires methylation analyis to secure diagnosis. There is currently no definitive grading, but clinical behaviour suggests WHO CNS grade 3.

Clinical

• Rare (1-3% of all brain tumor in adults).
• Usu. posterior fossa (75%).
• Supratentorial or spinal locations possible.
• Imaging may be similiar to Glioblastoma.
• 5-year OS: 50%.

Histology

• Often so variable, so molecular testing is essential to secure diagnosis.
• Astrocytic nature of tumor cells.
• Frequent mitoses.
• Elongated glial tumor cell processes ("piloid").
• Rosenthal fibers or eosinophilic granular bodies.
• Perivascular lymphocytic cuffing.
• Necrosis may be present.

IHC

• GFAP+ve.
• ATRX: nuclear loss in approx. 40%.

Molecular

• DNA Methylation profile of high-grade astrocytoma with piloid features is essential for diagnosis.
• MAPK genes often altered (NF1, BRAF fusion, FGFR1, KRAS).
• CDKN2A/B homozygous deletion.
• CDK4 amplification.
• TERT promotor mutations are rare.
• Absence of IDH1/2 hotspot mutation.

DDx:

• Glioblastoma
• Pleomorphic xanthoastrocytoma

See also

• Astrocytoma.
• Neuropathology_tumours#Infiltrative_astrocytomas