Embryonal neuroepithelial neoplasms of the CNS

Published on 19/03/2015 by admin

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Last modified 19/03/2015

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Embryonal neuroepithelial neoplasms of the CNS


Embryonal (primitive) neuroepithelial neoplasms make up approximately 5% of CNS neoplasms. Their features include:

In the WHO classification (2007), listed embryonal neuroepithelial neoplasms are:

Controversy surrounding the ontogeny of CNS embryonal neoplasms ensures that a revision to their classification appears in each new edition of the WHO ‘blue book’. In the latest version (2007), medulloblastoma is separated from CNS PNET, implying that the latter is extracerebellar. Four variants of medulloblastoma are listed, all of which have a biological behavior distinct from that of the classic tumor. Ependymoblastoma and medulloepithelioma are now listed under CNS PNET, alongside focally differentiated variants of the archetypal tumor, the CNS neuroblastoma and ganglioneuroblastoma.

A population of small undifferentiated cells with a high turnover is a common feature of CNS embryonal neoplasms. This and shared clinical features, such as presentation in childhood and an aggressive clinical course, originally encouraged the thesis that these neoplasms, including the medulloblastoma, have a common histogenesis and should thus be grouped as CNS PNETs. Initially, this approach had diagnostic and therapeutic utility. However, current biological evidence suggests that CNS embryonal neoplasms develop in anatomically restricted neural stem cells or progenitors and harbor distinct genetic aberrations, prompting a move away from the concept of ‘PNET’ as a unifying label. As molecular subgroups of these neoplasms are shown to be biologically distinct and targeted therapeutic agents are developed to their molecular aberrations, a classification based on detailed histopathological and molecular characteristics will evolve.


Many embryonal neoplasms are circumscribed, pink or gray neoplasms, which may contain areas of hemorrhage, necrosis, or calcification (Fig. 38.1). CNS neuroblastomas and medulloepitheliomas sometimes contain cysts. All embryonal neoplasms have the capacity to invade the brain and spinal cord, and this will often be evident microscopically, if not macroscopically. However, infiltration occurs to a variable degree, and is rarely as diffuse as demonstrated by some astrocytic tumors.

The texture of embryonal neoplasms varies. Some are soft, but some medulloblastomas in the lateral cerebellar cortex and some cerebral neuroblastomas tend to be firm because they contain areas of desmoplasia. Neoplastic cells occasionally metastasize through the CSF pathways (Fig. 38.2).


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