Pilocytic astrocytoma

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Pilocytic astrocytoma
Diagnosis in short

Pilocytic astrocytoma. Smear. H&E stain.
LM DDx piloid gliosis, oligodendroglioma, glioblastoma
Stains PAS-D +ve (eosinophilic granular bodies)
IHC GFAP +ve
Gross usually cerebellar +/-cystic
Site brain - usu. cerebellum

Prevalence common - esp. in children
Prognosis good (WHO Grade I)

Pilocytic astrocytoma, abbreviated PA, is a low-grade astrocytoma. It the most common glioma in children.

General

  • Low-grade astrocytoma - WHO Grade I by definition, but rare anaplastic forms have been described.
  • Classically in the cerebellum in children; most common glioma in children.[1]
  • The optic glioma is associated with neurofibromatosis 1.
  • Usually enhances after CM application

Gross

Features:[1]

  • Usually well-circumscribed.
  • Often cystic with mural nodule.

Microscopic

Features:[2]

  • Classically biphasic (though either may be absent):
    1. Fibrillar.
    2. Microcystic/loose.
  • Hair-like fibres ~ 1 micrometer; pilo- = hair.[3]
    • Best seen on smear or with GFAP IHC.
  • Rosenthal fibres - key feature.
    • May be rare. Not pathognomonic (see below).
  • Eosinophilic granular bodies.
  • Low cellularity - when compared to medulloblastoma and ependymoma.

Notes:

  • +/-Microvascular proliferation.
  • +/-Focal necrosis.
    • Necrosis with pseudopalisading more likely glioblastoma.
  • +/-Mitoses - not significant in the context of the Dx.

DDx (of Rosenthal fibers):[4]

  • Chronic reactive gliosis.
  • Subependymoma.
  • Ganglioglioma.
  • Alexander's disease (rare leukodystrophy).

DDx of pilocystic astrocytoma (brief):

Images

Smears

Sections

www:

Stains

  • PAS-D: eosinophilic granular bodies +ve.

IHC

Features:[6]

  • GFAP +ve (fibres).
  • CD68: may have a significant macrophage component.
  • KI-67: may be "high" (~20% ???).
  • Olig 2: Usually strongly present.[7]

Molecular

  • Alteration usually associated with the MAPK pathway.
  • KIAA1549-BRAF fusion transcripts most common in sporadic PA.
  • Rarely BRAF mutations, SRGAP3-RAF1 or FAM131B-BRAF fusions.

See also

References

  1. 1.0 1.1 Perry, Arie; Brat, Daniel J. (2010). Practical Surgical Neuropathology: A Diagnostic Approach: A Volume in the Pattern Recognition series (1st ed.). Churchill Livingstone. pp. 82. ISBN 978-0443069826.
  2. Perry, Arie; Brat, Daniel J. (2010). Practical Surgical Neuropathology: A Diagnostic Approach: A Volume in the Pattern Recognition series (1st ed.). Churchill Livingstone. pp. 82-4. ISBN 978-0443069826.
  3. URL: http://dictionary.reference.com/browse/pilo-. Accessed on: 24 November 2010.
  4. Munoz D. 9 Mar 2009.
  5. URL: http://path.upmc.edu/cases/case195.html. Accessed on: 8 January 2012.
  6. Perry, Arie; Brat, Daniel J. (2010). Practical Surgical Neuropathology: A Diagnostic Approach: A Volume in the Pattern Recognition series (1st ed.). Churchill Livingstone. pp. 84. ISBN 978-0443069826.
  7. Otero, JJ.; Rowitch, D.; Vandenberg, S. (Sep 2011). "OLIG2 is differentially expressed in pediatric astrocytic and in ependymal neoplasms.". J Neurooncol 104 (2): 423-38. doi:10.1007/s11060-010-0509-x. PMID 21193945.