medulloblastoma | Medulloblastome and PNET

Medulloblastome and PNET

Medulloblastoma is the most common of the primitive tumors Neuro-ectodermal or PNET. It develops in the cerebellum, most often at the level of the vermis. It is a malignant tumor whose tissue has the appearance of an embryonic tissue. It is invasive and can metastasize throughout the central nervous system, by the cerebrospinal fluid pathway. At the time of diagnosis, almost half of the children have metastases that are rarely symptomatic. The majority of these tumours occur before the age of 10 years (40% before 5 years and 75% before 10 years) but they can be seen in adolescents or young adults. Medulloblastoma represents about 1/3 of all tumours in the posterior fossa.

The PNET include:

The medulloblastoma, located in the posterior fossa, is the most common and best known of these tumors.
The Pinéaloblastome, located in the Espace sus-cancerinfratentorial.
Embryonic tumours with pluristratifiées rosettes (ETMR) can be located at the posterior fossa, as in the cancerinfratentorial space or the spinal cord or brainstem.
Undifferentiated PNET sit preferentially, but not exclusively, in the SUS-Tentorielle region.
Diagnosis
Intracranial hypertension is the earliest and most constant revealing sign associated with a more or less marked equilibrium disorder. Paralysis of the cranial nerves may occur, if there is an infiltration of the brainstem by the tumor. The attainment of the driving routes is usually later.

Therapeutic Strategy
Surgical ablation is usually the first step in treatment. In some cases (most often in the case of a metastatic disease), a simple biopsy will be performed initially to diagnose the disease and the removal of the tumor will be programmed after chemotherapy.

The post-operative reference treatment is an irradiation of the posterior fossa associated with irradiation of the brain and spinal cord (craniospinal irradiation). The combination of surgery and irradiation at these doses resulted in 5-year survival in the order of 50%, all risk levels combined. However, long-term surveillance of these patients has shown that such treatment results in predominantly cognitive and endocrine morbidity, all the more important as the child is younger at the time of treatment.

Currently, treatment is adapted to the age of the child because of the sequelae associated with radiation therapy in young children.

Children under the age of five
The post-operative treatment of children under 5 years of age with Medulloblastoma is adapted to the type of medulloblastoma. Medulloblastomas Nodular desmoplasiques are a very good form of medulloblastoma at this age whose treatment is based on exclusive chemotherapy with intravenous methotrexate and intraventricular. The survival of these young patients treated without radiotherapy is greater than 80% at 5 years.

For other forms of medulloblastoma, therapeutic strategies based on high-dose chemotherapy with hematopoietic stem cell transplantation are being evaluated to avoid or reduce radiation doses in These young children whose prognosis remains reserved.

Regarding the PNET or ETMR, the prognosis remains bleak. The treatment is based on chemotherapy associated with an age-appropriate dose radiation therapy.

Children over the age of five
The treatment is currently stratified as a risk group according to the quality of surgery, the presence of metastasis and the biological factors intrinsic to the tumor. Thus the standard risk group is defined by complete surgery of the tumor and the absence of metastasis and the absence of amplification of the MYC oncogene within the tumor.

These standard risk patients are currently treated with reduced-dose craniospinal irradiation followed by prolonged chemotherapy with 5-year survival of more than 80%. Recently, the presence of a mutation in the Betacaténine gene in the tumor has been identified as a very good prognostic factor within this standard risk group. A therapeutic dose reduction strategy for radiation therapy is being evaluated in these patients carrying this mutation.
For high-risk patients, the prognosis has improved significantly with therapeutic strategies involving several high-dose chemotherapy treatments and craniospinal irradiation.

The prognosis of undifferentiated PNET remains very bleak. Treatment is currently identical to high-risk medulloblastoma.