It is group of tumors with similar histological appearance that are thought to arise from germinal or matrix cells of the primitive embryonal neural tube. Ependymoblastomas, rare, malignant, tumors with distinct ependymal differentiation, are included together with medulloepitheliomas, neuroblastomas, ganglioneuroblastoma, pineoblastoma, and medulloblastomas in the group of embryonal tumors.

In the past, these tumors, along with medulloblastoma, were included in 'Primitive Neuroectodermal tumors (PNET)'.

Recently, WHO reserved the term PNET only to Medulloblastoma, irrespective of location.

The majority of these embryonal tumors are found infratentorially in the form of cerebellar medulloblastomas.

Other embryonal tumors are predominantly large tumors, often involving the deep supratentorial structures. The children are most commonly affected. In children, they account for 2.5% to 5% of all primary brain tumors.

In cases with ependymal differentiation (perivascular pseudorosettes and true rosettes), it is named 'ependymoblastoma'..

Seizures and focal neurological deficits, with features of raised ICT are the symptoms at presentation.

CT and MRI reveal a well differentiated, heterogenous, markedly enhancing hemispheric mass with varying degree of cystic or necrotic changes. Evidence of CSF dissemination is typically seen as focal or diffuse enhancement within the subarchnoid space and ventricular system.

Aggressive multimodality approach, similar to the management of medulloblastomas, is recommended.

Complete resection, and post operative craniospinal radiation is commonly used.

Chemotheray have taken a greater role in children.

The prognosis is poor, with few survivors beyond three years.

Medulloepithelioma: 

This is an extremely rare tumor, possibly derived from the primitive medullary plate and neural tube. Rubinstein considers it the most primitive and multi-potential neoplasm in neuro-oncology and a truly ‘embryonic tumor’. 

The tumor is essentially cerebral in location and is generally encountered early in life. 

It is usually soft, friable and hemorrhagic. 

Microscopically it presents a papillary and almost tubular arrangement of medium or tall columnar cells, recalling the structure of the primitive medullary epithelium. These cells are bounded by an internal limiting membrane and may be arranged in a single layer and show slight stratification.  Neither cilia nor blepharoplasts can be demonstrated and the nuclei are large, oval and vesicular.  The papillae and occasional solid cords of tumor cells rest on a prominent vascular connective tissue stroma which might be so proliferated as to create the impression of an additional vasoformative tumor. 

Generally, these primitive tumors do not exhibit any cellular maturation, but occasionally there may be evidence of a neuroblastic transformation in the majority of  tumors.  However, tissue culture experiments have shown that medulloblastomas are uniformly neuroblastic in virto. 

Neuroblastoma: 

Neuroblastomas are rare tumors occurring essentially during the first year of life.  Many occur as congenital tumors. These arise from immature neurons and characteristically, therefore, possess the ability to mature into adult neurons. Another feature is their ability to undergo  arrest of maturation and involution. 

They may arise in two situations, viz., cerebral and olfactory. Though extracranial examples are more common than cerebral forms, the histological features are similar in both regions. 

The histological features are comparable to those of cerebellar medulloblastoma. Generally, a highly cellular neoplasm is seen and this consists of fairly uniform cells resembling the cerebellar medulloblastoma, with scanty cytoplasm and a large deep-staining nucleus.  Homer-Wright rosettes may also be seen in up to 50 per cent of cases.  In many areas, islands of cells may be separated by strands of connective tissue.  Silver stains may show the presence of neurofibrillary material and in some areas, cells suggestive of immature neurons may be seen.  Secondary changes such as necrosis, hemorrhage and calcification are rare.  The undifferentiated variety has sheets of small tumor cells with dense circular nuclei.  With greater differentiation vaguely defined rosettes or small clusters of cells may be seen in places.  In either event, the tumor shows a considerable amount of connective tissue, specially a rich reticulin framework, which reaches up to the surface arachnoid mater.  On this account, the cerebral neuroblastoma, like the medulloblastoma, may be confused with a meningeal sarcoma.  Parts of the tumor may show some differentiation towards the formation of neurons. 

The tumors are of low grade malignancy and the olfactory examples are of relatively slow growth. Though highly radiosensitive, they are liable to recur and spread to adjacent regions.  The olfactory neuroblastoma (esthesioneuroblastoma) may possibly have its origin in the olfactory bulb and present as a paramedian frontal space occupying lesion. 

Recurrence after surgical removal and changes in histological features after radiation have been described.

Medulloblastomas: discussed elsewhere.

Pineoblastomas: discussed elsewhere.