Pilocytic astrocytoma

Pilocytic_astrocytoma]]

General

• Low-grade astrocytoma - WHO Grade I by definition.
• Classically in the cerebellum in children; most common glioma in children.
• The optic glioma associated with neurofibromatosis 1.

Gross

Features:

• Usually well-circumscribed.
• Cystic or solid.
• Do not smear. (Ref. ?)

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.
• Ganglioma.
• Alexander's disease (rare leukodystrophy).

DDx of pilocystic astrocytoma (brief):

• Piloid gliosis.
• Oligodendroglioma.
• Glioblastoma (uncommon - but important).

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).
  • 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% ???).

See also

• Neuropathology tumours.
• Astrocytoma.