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Medulloblastoma and Other Embryonal Tumors
Medulloblastoma is a malignant tumor of the cerebellum that primarily affects children, but can also occur in adolescents and adults. Its diagnosis today relies on precise histopathological and molecular characterization, which is essential for tailoring treatment to individual risk.
Medulloblastoma develops in the cerebellum, located at the back of the brain in the posterior fossa. It belongs to the group of embryonic tumors of the central nervous system. It can grow rapidly, and tumor cells can circulate in the cerebrospinal fluid and subsequently spread to other regions of the brain or spinal cord. This potential for dissemination justifies a comprehensive evaluation of the entire central nervous system at the time of diagnosis.
Medulloblastomas do not constitute a single disease. The current classification system combines the tumor’s microscopic appearance with its molecular characteristics. These data make it possible to distinguish several biological subgroups, refine the prognosis, and progressively adjust the intensity of treatment.
A Specific Classification
Embryonal tumor of the cerebellum. Molecular classification distinguishes between WNT-activated, SHH-activated, and non-WNT/non-SHH medulloblastomas, with the latter comprising groups 3 and 4.
Atypical teratoid and rhabdoid tumor is a rare embryonal tumor, often diagnosed in young children. Its diagnosis is based, in particular, on abnormalities in the SWI/SNF complex.
Embryonal tumor with multilayered rosettes is a rare condition that primarily affects very young children. Molecular analysis helps confirm the diagnosis.
Pineoblastoma, central nervous system neuroblastoma with FOXR2 activation, and other rare embryonal tumors now have their own diagnostic categories.
Why are molecular analyses essential?
Two tumors that appear similar under a microscope may belong to different biological groups. An integrated diagnosis combines histopathology, immunohistochemistry, and molecular biology. In some cases, the DNA methylation profile helps clarify the specific type of tumor.
Symptoms
The symptoms are primarily related to the tumor’s location in the cerebellum and to the obstruction of cerebrospinal fluid flow, which can cause intracranial hypertension. They may develop gradually and are not specific to a tumor.
Persistent headaches, often accompanied by nausea or repeated vomiting, unusual drowsiness, irritability, or visual disturbances.
Loss of balance, unsteady gait, falls, recent clumsiness, difficulty coordinating movements or holding up the head and trunk.
Double vision, recent strabismus, abnormal eye movements, facial asymmetry, or difficulty swallowing in certain situations.
Regression in learning, refusal to walk, behavioral changes, rapid increase in head circumference, or loss of previously acquired skills.
When to Seek Immediate Medical Attention
Repeated vomiting accompanied by headaches, unusual drowsiness, a seizure, weakness in a limb, or sudden problems with balance, vision, speech, or consciousness requires prompt medical evaluation. If you experience sudden or severe symptoms, contact emergency services.
Diagnosis and Staging
A brain MRI is the gold standard for visualizing the tumor and its relationship to neighboring structures. An MRI of the spine is performed to check for possible spread along the spinal cord. A brain MRI performed after surgery assesses any residual tumor.
Analysis of tissue collected during surgery or a biopsy confirms the diagnosis. It identifies the histological type, molecular subtype, and other abnormalities useful for risk stratification. A lumbar puncture with analysis of the cerebrospinal fluid may complete the evaluation, at a time deemed safe by the team after considering the neurosurgical context.
The level of risk therefore no longer depends solely on age, the presence of metastasis, and residual tumor volume. Molecular characteristics now play a major role. They make it possible to identify forms with a very favorable prognosis and others that require an intensified treatment strategy or the evaluation of new approaches.
A diagnosis discussed as a group
The case is presented at a multidisciplinary pediatric consultation meeting. Neuroradiologists, neurosurgeons, neuropathologists, pediatric oncologists, radiation oncologists, and laboratory scientists review the findings together to determine the most appropriate treatment strategy.
Treatments for Medulloblastoma
Treatment most often combines surgery, radiation therapy, and chemotherapy. The order, intensity, and specific approaches vary depending on the child’s age, the extent of the disease, residual disease after surgery, molecular subtype, other risk factors, and the child’s overall condition.
Neurosurgery
Surgery is generally the first step. The goal is to achieve as complete a resection as possible without causing disproportionate neurological sequelae. It also provides the tissue necessary for an integrated diagnosis. A cerebrospinal fluid shunt may be necessary in cases of hydrocephalus. A biopsy alone may be considered in specific situations where initial resection poses too great a risk.
Radiation Therapy
In children for whom it is indicated, radiation therapy usually involves craniospinal irradiation, designed to treat the entire brain and spinal cord, followed by a targeted dose to the tumor site. The dose depends on the risk group and the treatment protocol. High-precision techniques aim to minimize exposure to healthy tissue. Proton therapy may be considered in certain situations to reduce the dose received by organs located beyond the target.
In very young children, the brain is particularly vulnerable to the late effects of radiation. When the situation and treatment protocol allow, medical teams aim to delay radiation therapy, reduce the treatment volume, or avoid it altogether through appropriate chemotherapy strategies.
Chemotherapy
Chemotherapy complements surgery and radiation therapy. The drugs used and their schedule depend on the patient’s age and risk level. Certain treatment strategies for young children or high-risk cases may involve intensive chemotherapy supported by hematopoietic stem cells.
Risk-Based Treatments
Standard-risk cases may benefit from a treatment regimen combining craniocerebral radiation at an appropriate dose with chemotherapy. For high-risk cases, particularly those with disseminated disease or unfavorable biological characteristics, treatment may be intensified, and enrollment in a clinical trial may be considered. Conversely, research is evaluating strategies to reduce the intensity of treatment for certain groups with an excellent prognosis in order to minimize long-term effects without compromising the chances of cure.
Among the youngest children
Age alone is not sufficient to determine the treatment strategy. The histologic type, molecular subtype, extent of disease, and other risk factors are taken into account. Certain forms of SHH with nodular histology or extensive nodularity may have a favorable prognosis with treatment strategies that avoid radiation therapy, but treatment must be determined within a specialized protocol.
Other Embryonal Tumors
ATRT, ETMR, pineoblastoma, and other rare embryonic tumors are not variants of medulloblastoma. They have their own distinct biology and do not all respond to the same treatment. Their extreme rarity warrants expert diagnostic confirmation, discussion within specialized networks, and, when possible, inclusion in an appropriate registry or clinical trial.
The treatment strategy may combine surgery, conventional or intensive chemotherapy, and radiation therapy tailored to the patient’s age, tumor type, and extent of disease. The prognosis varies greatly depending on the specific subtype, molecular profile, and clinical situation. It is therefore not appropriate to provide a single figure for all of these diseases.
Follow-up and Long-Term Effects
Follow-up care combines regular MRI scans with clinical monitoring. It is designed not only to detect a possible relapse, but also to prevent, identify, and manage the effects of the disease and its treatments on the child’s development.
A neuropsychological evaluation can identify difficulties with attention, memory, processing speed, or organization and help guide academic accommodations.
Craniospinal radiation therapy and certain other treatments may warrant long-term endocrinological monitoring of growth, thyroid function, and puberty.
Hearing, neurological, and motor assessments are offered depending on the treatments received and the difficulties observed.
Support can be provided to the child, his or her parents, and siblings during treatment and as they return to their daily lives.
Long-term, personalized follow-up
Long-term risks vary from child to child. The follow-up plan depends on the age at diagnosis, the location of the tumor, the type of surgery, the medications received, the doses and volumes of radiation therapy, and each patient’s specific needs.
Patient Care at Gustave Roussy
At Gustave Roussy, the treatment strategy is coordinated by a team specializing in pediatric oncology and discussed during multidisciplinary team meetings. Depending on the situation, the care pathway combines the expertise of teams in neuroradiology, neuropathology, molecular biology, partner neurosurgery, radiation therapy, pediatric oncology, rehabilitation, and supportive care.
The care pathway may include psychological support, pain management and nutritional care, neuropsychology, rehabilitation, continued schooling, adapted physical activity, social support, information on fertility preservation, and long-term follow-up.
Research and Clinical Trials
The research aims to refine molecular stratification, reduce treatment for patients with a very good prognosis, improve strategies for high-risk or relapsed cases, and minimize long-term effects. It also focuses on new therapeutic targets, new medications, and tools capable of better predicting response to treatment.
Participation in a clinical trial is always voluntary. It is offered only when appropriate for the situation and is accompanied by detailed information provided to the child and their family, as well as informed consent in accordance with current regulations.