Supratentorial PNET

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 (medulloblastoma, atypical teratoid rhabdoid tumor, and PNET). 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 (CSF). 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 (medulloblastoma, atypical teratoid rhabdoid tumor, and PNET). 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 (CSF). 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 (MRI) and computed tomography (CT) are used to diagnose PNETs. Even though a universal treatment plan hasn't been stablished yet, common strategies involve chemotherapy and radiotherapy for individuals older than 3 years of age. Their efficacy, however, is still controversial. Surgery can be used to remove mass affected by tumorous cells. The prognosis of the disease is more positive for adults than for children, who have a higher probability of having sequelae from the tumor. 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. The differentiation between primitive neuroectodermal tumor in the central nervous system and medulloblastoma is recent. According to the World Health Organization, both tumors have the same histology but primitive neuroectodermal tumors occur outside the cerebellum. Moreover, it has been documented that both have different genetic expression and mutations. Another essential difference between them is the location of their respective blood vessels within the brain. It has also been theorized that PNETs influence mainly glia cells while medulloblastomas influence mainly neural behavior, however such theory hasn't been confirmed yet. Medulloblastomas are more frequent than PNETs, representing 10% of all child deaths caused by cancer. They also present better prognosis: children affected by medulloblastoma reach the 5 year survival mark in 70-80% of cases, while children affected by PNET reach the 5 year survival mark in less than 50% of cases. The rate of PNETs in not correlated with sex, but it shows a correlation with age. Most cases occur in children around 5 years of age, having a very low frequency in adults. Regarding genetic mutations, a specific type of gene alteration that directly leads to this tumor hasn't been defined yet. However, a positive correlation between individuals with Li-Fraumeni syndrome with a mutation in the gene p53 and PNET has been reported. A significant number of individuals with mutations on the rb tumor suppressor gene have also developed the tumor. Such gene encodes for the protein Rb responsible for stopping the cell cycle at the G1 phase. Another possible contributing factor are mutations in the CREB-binding protein, whose function includes activating transcription, but this interaction still need to be studied further. It has also been presumed that the tumor can arise from cranial irradiation. Most children that develop primitive neuroectodermal tumors are diagnosed early in life, usually at around 3-6.8 years of age. Symptoms patients present at time of diagnosis include irritable mood, visual difficulties, lethargy, and ataxia. The circumference of the patient's head might also suffer an enlargement and they might be subject to seizures, especially if they have less than one year of life. Several analysis can be used to determine the presence of the disease. Physical examinations showing papilledema, visual field defects, cranial nerves palsy, dysphasia, and focal neurological deficits are evidences for possible tumor. PNETs can also be spotted through computed tomography (CT) and magnetic resonance imaging (MRI). In images produced by MRIs, an irregular augmentation among a solid mass will indicated the presence of tumor. However, the results of MRIs are usually ambiguous in defining the presence for this specific tumor. In CT scans, the presence of PNETs will be indicated by an elevated density and an increase in volume of the brain. The CT scan can also show calcification, which is present in 41-44% of PNET cases. Since the tumor can be replicated in other parts of the nervous system through the cerebrospinal fluid (CSF), a CSF analysis can also be conducted. A spinal MRI is a fourth type of analysis that is useful in investigating the level of tumor propagation to the spinal cord.