Medulloblastoma is the most common malignant brain tumor in childhood (between 20-30% of central nervous system tumors in children). It is slightly more common in boys than girls.
In USA each year between 300 and 350 brain tumors are diagnosed in children , the most common solid tumors in children and the leading cause of cancer-related death in childhood. Of these, 30% are medulloblastomas, the most common malignant brain tumors in childhood that originate in a part of the brain called the cerebellum . The cure rate is very high , but there are still 30% of children with this tumor that is resistant to current treatments and requires further investigation.
What is medulloblastoma?
Medulloblastoma is a cancerous brain tumor, also called primitive cerebellar neuroectodermal tumor (PNET, for its acronym in English) that is located at the base of the skull or posterior fossa, specifically, in the cerebellum . They are tumors that, if left untreated, can spread, through the cerebrospinal fluid, to other parts of the brain and to the spinal cord. Spread to other parts of the body is very rare.
Why it occurs
Medulloblastoma is an embryonal- type tumor , that is, a tumor that begins in the fetal cells of the developing brain.
It is not a genetic tumor , but Turcot, Li-Fraumeni and Gorlin syndromes have been shown to increase the risk of developing medulloblastoma.
The cause of medulloblastoma is unknown . Different potential risk factors, environmental and infectious have been studied, but there is still no clear evidence.
Symptoms of Medulloblastoma
The growth of a tumor in the posterior fossa of the central nervous system causes symptoms related to the tumor itself and also due to increased pressure within the brain. Due to its location in the posterior fossa, cerebellar symptoms such as dysmetria, dysarthria, and ataxia are common .
The most frequent symptoms are:
- Severe headaches
- Nausea and vomiting
- Double vision (diplopia).
- Poor coordination and clumsiness.
- Unstable gait (ataxia).
- Writing problems
- Dysarthria (difficulty in articulating speech).
If the tumor has spread and is affecting the spinal cord, the child may have:
- Back pain.
- Walking difficulties
- Problems controlling sphincters (bladder and bowel).
In infants , as they have open cranial sutures, they are protected from increased intracranial pressure and tumors, such as medulloblastoma, present with hydrocephalus causing progressive asymptomatic macrocephaly and bulging fontanelles and non-specific symptoms such as lethargy, irritability, feeding difficulties , and developmental delay.
If the child’s symptoms are compatible with a possible medulloblastoma, the tests that allow us to detect the tumor are CT and magnetic resonance imaging (MRI) . Later, surgery and analysis of the tumor sample in the laboratory will allow us to confirm the diagnosis of medulloblastoma and the subtype.
Types of medulloblastoma
The current 2016 World Health Organization (WHO) classification combines an integrated diagnosis , including histology and genetics . All medulloblastomas are classified as WHO grade IV , which is the highest grade of malignant tumor. The histological variants of previous classifications: classic (the most frequent), desmoplastic nodular and anaplastic or large cells, continue to be part of the current classification.
Four molecular subgroups with genetic alterations, histological and demographic variants and specific clinical results have been agreed upon:
- Wnt / βcatenina : it represents a prevalence of 11% . It occurs in older children and adolescents with a peak incidence of around 10 years and the same in boys as in girls. WNT tumors arise from dorsal brainstem cells and are rarely metastatic at diagnosis. Most have a deletion of one copy of chromosome 6 (monosomy 6).
- Sonic-Hedgehog : make up 33%. They have a bimodal incidence, beginning in infants under 3 years of age and also in adolescents over 16 years of age and young adults . They occur with the same frequency in both sexes. They appear laterally, within the cerebellar hemispheres, and metastases are present at diagnosis in approximately 25% of cases. Mutations PTCH1, SMO and SUFU have been associated with this subtype.
- Group 3 : represent 25% and are typically diagnosed in infants and children (the maximum incidence is between 3 and 5 years) with a male preponderance (2: 1). It is the subtype with the highest prevalence of metastasis at diagnosis (up to 45%). The tumor usually arises from the midline of the cerebellum. It has the worst prognosis and is frequently associated with myc amplification.
- Group 4 : it is the most frequent subtype and represents 35%. They develop in all age groups with a peak incidence of around 9 years and are three times more common in men . The most common histologic variant is classic medulloblastoma. They generally arise in the midline of the cerebellum, and metastatic disease at diagnosis is seen in 35-40%.
The surgery is the first step to treat and the goal is to remove the tumor , leaving the fewest possible sequelae. After surgery, the patient is treated with brain and spinal radiation therapy and chemotherapy . Radiation therapy cannot be administered in children under 3 years of age, due to the important consequences that this could have on their later development, which is why chemotherapy protocols are more intense in young children.
Medulloblastoma is the most common brain tumor in childhood and its survival has improved in recent decades thanks to the incorporation of chemotherapy.
The prognosis of this tumor is related to 3 factors : the age of the patient, the presence of metastasis at the time of diagnosis and the existence of residual tumor after surgery, with a worse prognosis in children under 3-5 years of age, in patients with disease disseminated or with tumor remnant> 1.5cm.
If the medulloblastoma has not spread to other areas, survival is around 70-80%. If the spread reached the marrow, 60%.
Children under the age of three often have lower survival rates because their disease tends to be more aggressive.
In the treatment of medulloblastoma, efforts should focus on adjusting the intensity of the treatment and minimizing its sequelae in the medium and long term, as well as investigating therapeutic strategies to increase survival in those with the worst prognosis.
What you should know…
- It is the most common malignant brain tumor in childhood (between 20-30% of central nervous system tumors in children). It is slightly more common in boys than girls.
- Medulloblastoma and other embryonal brain tumors comprise the most common malignant tumors of the central nervous system in children under 4 years of age and the second in children and adolescents up to 19 years of age.
- The average age of debut is 6 years. In the United States, between 250 and 300 medulloblastomas are diagnosed annually. In USA, about 90. Most are diagnosed in children under 16 years of age, and rarely in adults.