page_title: Central nervous system primitive neuroectodermal tumor
section_title: Classification
hierarchical_section_title: Central nervous system primitive neuroectodermal tumor / Classification
caption_attribution_description: English: Ependymoblastomatous rosette in a case of ependymoblastoma. H&amp;E staining. 400x
context_page_description: A central nervous system primitive neuroectodermal tumor, often abbreviated as PNET, supratentorial PNET, or CNS-PNET, is one of the 3 types of embryonal central nervous system tumors defined by the World Health Organization. It is considered an embryonal tumor because it arises from cells partially differentiated or still undifferentiated from birth. Those cells are usually neuroepithelial cells, stem cells destined to turn into glia or neurons. It can occur anywhere within the spinal cord and cerebrum and can have multiple sites of origins, with a high probability of metastasis through cerebrospinal fluid.
  PNET has five subtypes of tumors: neuroblastoma, ganglioneuroblastoma, medulloepithelioma, ependymoblastoma, and not otherwise specified PNET. It is similar to medulloblastoma regarding histology but different regarding genetic factors and tumor site. It is a rare disease occurring mostly among children, accounting for 1.9 to 7% of childhood brain tumors. Symptoms involve emotional, visual, motor, and speech defects. Magnetic resonance imaging and computed tomography are used to diagnose PNETs.
context_section_description: The World Health Organization has classified the central nervous system primitive neuroectodermal tumors into five subtypes: neuroblastoma, ganglioneuroblastoma, medulloepithelioma, ependymoblastoma, and not otherwise specified PNET. The last one encompasses the PNETs with varying characteristics that hasn't been well defined yet. Neuroblastomas are PNETS that involve the process of cell differentiation into neurons, while ganglioneuroblastomas are PNETs that involve ganglion cells.
  Medulloepithelioma, on the other hand, are tumors involving the constant cell division on the epithelium tissue where bundle of neuron endings are located. Such tissue will differentiate into a similar form as the embryonic neural tube, also known as the starting structure of the central nervous system. Medulloepitheliomas also present a pattern known as rosettes, characterized by the arrangement of a bundle of cells into circular shapes and around a center or a neuropil. Ependymoblastoma also present rosettes as well as a higher density of cells. It involves the process of differentiation into ependymal cells.
  Further classification types have come up but not yet approved by the World Health Organization. The term "embryonal tumor with abundant neuropil and true rosettes", or ETANTR, has been proposed as a sixth subtype of PNET. However, the still unofficial term "embryonal tumor with multilayered rosettes" (ETMR) has been more frequently used and encompasses ETANTRs, medulloepitheliomas, ependymoblastomas, and variants of PNETs  with presence of rosettes and with no well defined classification.
caption: Rosettes in Ependymoblastoma histology
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