Primitive neuroectodermal tumour

CNS Primitive neuroectodermal tumour, abbreviated CNS-PNET, is an uncommon neuropathology tumour in the group of embryonal tumours.

Primitive neuroectodermal tumour
Diagnosis in short
CNS primitive neuroectodermal tumour H&E stain.
Synonyms	CNS-PNET
LM DDx	small round blue cell tumours
IHC	S-100 +ve, Syn +/-ve
Site	brain, spinal cord
Prevalence	rare - typically in young adults
Prognosis	poor (WHO Grade IV)

It is also known as supratentorial primitive neuroepithelial tumour (supratentorial PNET).

General

• Should not be confused with peripheral primitive neuroectodermal tumour (abbreviated pPNET), AKA Ewing sarcoma.
• Currently contains a heterogenous group of poorly differentiated WHO grade IV tumours. Major reoganisation of this group will occur in the upcoming WHO classification.
• Mainly children and adolescents.
• Cerebral hemisphere, brain stem or spinal cord.
• There are currently five ICD-O codes assigned within this group:
  • 9473/3 CNS-PNET, NOS.
  • 9500/3 CNS neuroblastoma.
  • 9490/3 CNS ganglioneuroblastoma.
  • 9501/3 Medulloepithelioma.
  • 9392/3 Ependymoblastoma.

Microscopic

Features:

• Small round blue cell tumour.
  • Focal differentation into astrocytic, neuronal or ependymal phenotypes possible.

Immunohistocehmistry

• S-100 +ve.
• INI1 +ve (loss defines tumour as ATRT).

DDx:

• Small round blue cell tumours
• Medulloblastoma
• ATRT
• Embryonal tumour with abundant neuropil and true rosettes (ETANTR).

Images

www:

• Primitive neuroectodermal tumour - several images (upmc.edu).
• GBM with PNET component - several images (upmc.edu).

See also

• Neuropathology tumours.