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Medulloblastoma

What is Medulloblastoma?

Medulloblastoma is a cancerous tumor of the brain. It is the most common malignant brain tumor in children, accounting for 20% of childhood central nervous system (CNS) tumors. There are between 250 and 500 new cases of pediatric medulloblastoma every year in the United States.

These tumors are most common in children under 16 years of age and are most often diagnosed between 5 and 9 years of age. However, medulloblastomas may be seen in older teens and, less commonly, in adults.

Illustration showing the posterior fossa structures of the brain within a child's head

Medulloblastoma begins in the cerebellum. The cerebellum is found in a region of the brain called the posterior fossa.

Medulloblastoma begins in the cerebellum, an area in the back of the brain. Specifically, the cerebellum is found in the lower rear part of the brain, in a region known as the posterior fossa. Functions of the cerebellum include the control of movement, balance, posture, and coordination.

Medulloblastomas are fast growing, and these tumors often spread to other parts of the brain and spinal cord. Most medulloblastomas are located in the middle of the cerebellum by the fourth ventricle.

Medulloblastoma can be divided into four subgroups based on molecular features of tumor cells:

  1. WNT subtype - pronounced “wint”
  2. SHH subtype – also known as Sonic hedgehog (SHH)
  3. Group 3
  4. Group 4

The specific medulloblastoma subgroup influences prognosis. Doctors use subgroups to classify patients into risk categories. This information helps doctors plan appropriate treatments.

Treatment for medulloblastoma includes surgery to remove as much of the tumor as possible. Radiation therapy is used after surgery to kill any remaining cancer cells. Chemotherapy is also used together with surgery and radiation therapy.

The overall survival rate for childhood medulloblastoma is 70-80% if the disease has not spread. If the disease has spread, the average survival rate is about 60%. However, the specific type of medulloblastoma tumor, including molecular subgroup, can influence treatment and prognosis.

Risk Factors for Medulloblastoma

Certain changes in genes and chromosomes within the tumor cell are associated with the development of medulloblastoma. Usually, it is not known why these genetic changes occur.

Most medulloblastomas occur in children between ages 5 and 9 years old. It is rare in infants and adults. Medulloblastoma is slightly more common in boys than in girls.

Some children may be at increased risk for brain tumors due to rare inherited conditions. These syndromes include Gorlin’s syndrome, Turcot syndrome, and Li-Fraumeni syndrome.

Signs and Symptoms of Medulloblastoma

Symptoms of childhood medulloblastoma depend on several factors including the size and location of the tumor and the child’s age and stage of development.

Medulloblastoma symptoms include:

  • Headache
  • Nausea and vomiting, often worse in the morning 
  • Fatigue or changes in activity levels
  • Dizziness
  • Loss of balance, clumsiness
  • Problems with handwriting
  • Change in vision

If there is spread of tumor to the spinal cord, symptoms may include:

  • Back pain
  • Problems walking
  • Problems urinating or change in bowel function

As the tumor grows, it often blocks the normal flow of cerebrospinal fluid. This causes a buildup of fluid within the brain known as hyrodcephalus. The fluid increases pressure on the brain (intracranial pressure). Many of the symptoms of medulloblastoma are due to the increased pressure against brain tissue.

Diagnosis of Medulloblastoma

Doctors evaluate medulloblastoma in several ways.  

  • A health history and physical exam helps doctors learn more about symptoms, general health, past illnesses, and risk factors.
  • A neurological exam measures different aspects of brain function including vision, hearing, muscle strength, balance, coordination, and reflexes.
  • Imaging tests are used to help identify the tumor. Magnetic resonance imaging (MRI) of the brain is the main imaging technique that is usually used to evaluate medulloblastoma. An MRI is also done after surgery to see if any tumor remains and to look for spread of disease.
  • A lumbar puncture may be performed after surgery to look for cancer cells in the cerebrospinal fluid.
  • After the tumor is removed during surgery, tissue from the tumor is examined to diagnose medulloblastoma. A pathologist looks at the tissue sample under a microscope to identify cell features such as size and shape. Histological features can help predict outcome. This information can help doctors classify patients by risk and plan appropriate treatments.

Microscopic features of the tumor cells such as the size and shape are used to classify medulloblastoma tumors by histology:

  • Classic medulloblastoma is made up of small, round cells. The cells are close together and have dark nuclei.
  • Desmoplastic/nodular (DN) medulloblastoma appears as circular nodules ringed by connective tissue with cells closely packed together.
  • Medulloblastoma with extensive nodularity (MBEN) shows more nodular regions within the tissue.
  • Anaplastic medulloblastoma is made up of cells that are irregularly shaped.
  • Large cell medulloblastoma has tumor cells with large nuclei.

Anaplastic and large cells often occur together and are grouped as large/cell anaplastic (LCA) tumors.

Sagittal MRI with arrow pointing to medulloblastoma

Medulloblastoma in sagittal MRI

Axial MRI with arrow pointing to medulloblastoma

Medulloblastoma in axial MRI

Molecular Subtypes of Medulloblastoma

Tissue from the tumor is also analyzed for biomarkers that give information on the genetic and molecular features of the tumor cells. Based on the molecular profile, medulloblastomas are grouped as WNT subgroup, SHH subgroup, Group 3, or Group 4.

Tumor location within the cerebellum can provide a clue as to the molecular type of medulloblastoma. WNT tumors tend to occur along the midline of the cerebellum. SHH tumors tend to be found in the lateral part of the cerebellum.

Staging of Medulloblastoma

Tissue histology and molecular features of the tumor cells are used to categorize patients with medulloblastoma and predict outcomes. This helps doctors more specifically match treatment plans to medulloblastoma risk group.

Medulloblastoma may also be classified by metastasis:

  • M0: The tumor is localized with no spread of disease.
  • M1: Tumor cells are found in the cerebrospinal fluid (CSF).
  • M2: There is evidence of spread of disease within the brain (intracranial).
  • M3: The tumor has spread to the spine.
  • M4: The tumor has spread outside the central nervous system (CNS). Common sites for metastases include the bones, lungs, and liver.

Prognosis for Medulloblastoma

The overall 5-year survival rate for pediatric medulloblastoma is approximately 70-80% if the disease has not spread. For high risk patients, the survival rate is about 60-65%.

Factors that affect chance of recovery include:

  • Histology of tumor cells.
    • Children under 3 years of age: Desmoplastic tumors are associated with a better outcome compared to classic or LCA tumors
    • Children over 3 years of age: LCA tumors are associated with a poorer outcome compared to classic or desmoplastic tumors
  • Molecular features of the tumor and changes in genes or chromosomes including medulloblastoma subtype (WNT, SHH, Group 3, or Group 4). WNT tumor subtypes have a very good prognosis, while prognosis for Group 3 tumors are less favorable. The other two subtypes have an intermediate prognosis.
  • Whether the cancer is localized or has spread to other parts of the brain or spinal cord. Localized disease is associated with a better prognosis.
  • Whether surgery is able to completely remove the tumor. Chance of cure is higher if the tumor can be completely resected.
  • Age at diagnosis. The influence of age on prognosis depends on the tumor subgroup and other features. However, radiation therapy is not usually used in infants and young children under 3 years of age.
  • If the cancer is new or if it has come back (recurrent). Recurrent disease is associated with worse outcomes.
Medulloblastoma Subgroup
General Patient Characteristics
Histology
Metastasis at Diagnosis
5-year Survival
Overall Prognosis
WNT subtype
~10% of medullobastomas
Most common in older children and teens; rare in infants
Classic;
Very rare Large Cell Anaplastic
5-10%
>90% survival
Very good
SHH subtype
~30% of medulloblastomas
Most common in young children under 3 years of age and older adolescents/adults
Nodular desmoplasatic;MBEN;Classic;
Large Cell Anaplastic
~15-20%
~75% survival
Intermediate, but infants have a better prognosis
Group 3
~25% of medulloblastomas
Most common in Infants and young children; rare in teens; more common in males
Classic and Large Cell Anaplastic
~30-45%
~50% survival
Poor
Group 4
~35% of medulloblastomas
Found in all age groups but rare in infants; more common in males
Classic; rarely Large Cell Anaplastic
~35-40%
~75% survival
Intermediate

Treatment of Medulloblastoma

Treatment for medulloblastoma includes surgery, radiation to the brain and spine (except in infants and young children), and chemotherapy.

Current risk-based approaches to medulloblastoma treatment classify patients based on clinical and molecular features and predicted outcomes. Doctors consider:

  • Molecular subgroup
  • Whether surgery completely removed the tumor
  • Presence of metastatic disease
  • Tumor histology
  • Genetic features of the tumor

The goal of a risk-based approach is to achieve survival while lowering the risk of side effects due to treatments. For patients who are predicted to have good outcomes, lower intensity therapy can reduce long-term problems from radiation and chemotherapy. For high-risk patients, more intensive therapy can improve chance of survival.

Patients may be offered treatment within a clinical trial.

  1. Surgery to remove as much of the tumor as possible is a main treatment for medulloblastoma. The goal is gross total resection, or complete removal of the tumor. However, location of the tumor may limit how much can be removed.

  2. Radiation therapy is usually used after surgery for medulloblastoma. The dose of radiation therapy depends on the stage of disease. Because of the potential for late effects due to treatment, radiation therapy is not used in very young children.

    Proton beam radiation therapy – In this type of radiation therapy, the amount of energy and how deep it goes into the tumor can be tailored to match each tumor’s size and shape. The radiation can stop at the tumor site. That means it doesn’t affect healthy tissue and organs on the other side of the tumor. This allows doctors to aim high doses of radiation at tumors and minimize damage to nearby healthy cells. Not every center offers proton therapy.

  3. Chemotherapy is usually used along with radiation therapy and surgery to treat medulloblastoma. In very young children, chemotherapy may be used to help delay radiation until the child is older. High-dose chemotherapy with stem cell rescue may also be used.

Medulloblastoma in Infants

The SHH subgroup is the most common medulloblastoma in children under 3 years of age followed by Group 3 tumors. SHH tumors in infants tend to have a favorable histology and molecular profile. These children often do well with surgery followed by chemotherapy without radiation.

Non-SHH medulloblastoma in infants is harder to treat, especially if there is metastatic disease. Treatments such as focal radiation therapy and high-dose chemotherapy with stem cell rescue may be tried, but cure is difficult to achieve. Side effects may outweigh the possible benefits in some cases.

Life After Medulloblastoma

Increased understanding of the molecular basis of medulloblastoma has led to improved rates of survival in recent years. However, survivors of medulloblastoma often suffer a variety of treatment-related complications. Ongoing follow-up care is needed to monitor patients for recurrence of disease and address long-term and late effects of treatment. Care should also include appropriate rehabilitation and neurological consultation.

About 25% of children who have surgery for medulloblastoma will develop posterior fossa syndrome. This syndrome usually develops within a few days after surgery. Symptoms include changes in speech, swallowing, motor function, and emotions. Symptoms can be mild or severe, and most children improve over time. The cause of posterior fossa syndrome is not known, and it is not possible to predict which patients will be affected.

Medulloblastoma survivors have an increased risk of specific late effects related to treatment. These include problems with endocrine function, cognition, hearing, fertility, and heart and lung function as well as increased risk of second cancers. Children treated for medulloblastoma often have difficulties in school, work, and relationships. They may have lower physical fitness and physical function. Regular physical checkups and screenings by a primary care physician are important to watch for health problems that can develop years after therapy. Support services such as mental health and academic resources can also promote quality of life for survivors. 

More: Life After Brain Tumors


Reviewed: June 2018