High-grade astrocytoma with piloid features

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High-grade astrocytoma with piloid features
Diagnosis in short

High-grade astrocytoma with piloid features. H&E stain.
LM DDx astrocytoma, PXA, glioblastoma
Stains PAS-D +ve (eosinophilic granular bodies)
Gross usually cerebellar
Site brain - usu. cerebellum

Prevalence very rare - esp. in children
Prognosis poor (analog to WHO Grade III)

High-grade astrocytoma with piloid features (HGAP) 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.


  • 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%.
  • De novo cases in the setting of neurofibromatosis 1 reported.
  • Tumors may have history of previous radiation.


  • 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.



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


  • 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.


  • Poor, but better than conventional glioblastoma.[1]
  • Prognostic unfavourable paramters include: Necrosis, Mitoses and previous radiation.


See also

  1. Rodriguez, FJ.; Scheithauer, BW.; Burger, PC.; Jenkins, S.; Giannini, C. (Feb 2010). "Anaplasia in pilocytic astrocytoma predicts aggressive behavior.". Am J Surg Pathol 34 (2): 147-60. doi:10.1097/PAS.0b013e3181c75238. PMID 20061938.