High-grade astrocytoma with piloid features

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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:

See also

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