The clinical, radiological and histopathological features of cerebral primitive neuroectodermal tumours.

The clinical, radiological and pathological features of eight cases of supratentorial primitive neuroectodermal tumour are reviewed. These are tumours of children and young adults presenting with symptoms and signs of raised intracranial pressure. Radiologically they are characterized by a large enhancing mass lesion exciting little or modest surrounding oedema, with a propensity to develop in the frontal lobes. One tumour exhibited the pathological features of a primitive neuroectodermal tumour (PNET) with ependymal differentiation (ependymoblastoma). The rest showed no light microscopy patterns to indicate differentiation. Immunohistochemistry was helpful as it excluded other causes of a 'small blue cell' tumour but did not help in assessing differentiation. Ultrastructural examination of this group of apparently undifferentiated tumours showed focal markers of neuronal differentiation. Although features of neuronal differentiation can be found ultrastructurally in these tumours this is only evident after prolonged searching, often of several blocks, making assessment very prone to sampling errors. The term PNET thus remains appropriate and serves to group such tumours together to facilitate rational clinical management.