Pilocytic astrocytoma

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 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.
• The optic glioma is associated with neurofibromatosis 1.
• Usually enhances after CM application

Gross

Features:

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

Microscopic

Features:

• Classically biphasic (though either may be absent):
  1. Fibrillar.
  2. Microcystic/loose.
• Hair-like fibres ~ 1 micrometer; pilo- = hair.
  • 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):

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

DDx of pilocystic astrocytoma (brief):

• Piloid gliosis (esp. in sellar lesions).
• Oligodendroglioma.
• Glioblastoma (uncommon - but important).
• Tanycytic Ependymoma
• Pilocytic tumor components may be found in Ganglioglioma, DNET, RGNT

Images

Smears

• 

  Bipolar cells with hair-like processes - smear - very high mag. (WC)

• 

  EGBs - smear. (WC/AFIP)

• 

  Rosenthal fibres - smear. (WC/AFIP)

Sections

• 

  Rosenthal fibres. (WC)

• 

  Occasional plomorphism (WC)

• 

  Microvascular proliferation (WC)

www:

• Rosenthal fibre (ouhsc.edu).
• Pilocytic astrocytoma (upmc.edu).
• Pilocytic astrocytoma - another case (upmc.edu).
• Pilocytic astrocytoma - pennies on a plate (upmc.edu).
• Pilocytic astrocytoma (upmc.edu).

Stains

• PAS-D: eosinophilic granular bodies +ve.

IHC

Features:

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

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

• Neuropathology tumours.
• Astrocytoma.