Medulloblastoma

The term medulloblastoma refers to a malignancy that develops in the cerebellum. This type of tumor accounts for about 7-8% of intracranial malignancies and around 30% of all brain tumors in children [1, 2].

What is Medulloblastoma?

A medulloblastoma is considered to be the most commonly occurring brain malignancy in children. The tumor develops in the cerebellum which is the portion of the brain that is located near the base of the skull. This part of the brain is responsible for voluntary movement coordination such as walking and fine motor skills. A tumor of this type is thought to have been originated from undeveloped brain cells. This condition progresses rapidly and may spread to other areas of the brain such as the brain or the spinal cord [1, 2, 3, 4]. Figure 1 shows a brain scan of a patient with medulloblastoma.

Staging

The staging system that is used in the classification of medulloblastoma is the Chang Staging System. This system will be able to describe the extent of the conditions with the aid of diagnostic tests [5].

• T1- Medulloblastoma is less than 3cm in diameter
• T2- The tumor is equal or greater than 3cm in diameter
• T3a- The mass is larger than 3 cm in diameter and have extended
• T3b- The tumor which diameter is bigger than 3cm has extended into the brainstem
• T4- The size of tumor has exceeded 3cm and it has grown beyond the aqueduct of Sylvius and beyond the posterior fossa
• M0- There are no evidence of metastasis
• M1- Tumor cells is present in the CSF
• M2- The tumor is found beyond the original site
• M3- There is gross nodular seeding found in the subarachnoid space of the spine
• M4- The mass have metastasized outside of the cerebrospinal system

Causes and Risk Factors

Majority of all medulloblastoma cases is unknown but some cases are associated with the occurrence of inherited genetic disorders. Examples of these condition are Turcot syndrome, Li-Fraumeni syndrome and nevoid basal cell carcinoma syndrome. This tumor commonly develops in children who are less than 8 years old and around half of these patients are younger than 6 years. Medulloblastoma is more commonly found in boys than in girls [6].

Signs and Symptoms

Some of the symptoms that may exhibit in a patient with medulloblastoma may include increasing head circumference, visual problems secondary to papilledema, later gaze paresis and diplopia. A lesion that has formed in the cerebellar vermis may lead to nystagmus. Involvement of the foramen magnum may lead to torticollis. Signs and symptoms that are linked with an elevation of intracranial pressure include, nausea, vomiting, headache, lethargy, fatigue, changes in personality and occurrence of seizures [2, 6].

Diagnosis

Health history and physical examination

Patients who have a developing medulloblastoma may seek consultation primarily due to symptoms associated with increased ICP. Those who are nonverbal may exhibit this through a change in the behaviour. The physician will identify when the symptoms have started to appear and whether have been worsening. Relief of the presenting signs will be noted as well. The physical examination aspect will identify all the other symptoms that may be present. The examination will include a neurologic status exam and assessment of the cranial nerves [2, 4].

Imaging studies

Magnetic resonance imaging with gadolinium DTPA is the imaging test of choice for medulloblastoma. It allows a multiplanar view with little bony artefact in the posterior fossa. Although this is the case, doing this test to children must be considered very carefully. Sedation is required for children before undergoing MRI but this can increase the level of carbon dioxide in the brain [2, 4].

Cerebrospinal fluid cytology

Examining the patient’s CSF is important in staging the medulloblastoma. The CSF will be collected either by lumbar puncture or a ventricular drain and it will be tested for the presence of tumor cells [2, 4].

Treatment

The treatment for medulloblastoma depends on the stage of the tumor but removal of the tumor through surgery is done whenever possible. The brain can accommodate a small elevation of intracranial pressure but changes in the mental status of the patient may indicate that the ICP is reaching its threshold. Frequent monitoring of the neurological status of the patient is important. Any decline in the mental status may warrant a need for mannitol administration or placement of a ventricular drain [2, 4, 6].

Surgery

The goal of the surgical procedure is to remove as much of the tumor as possible. After the surgery, the patient will undergo a MRI scan to assess the presence of residual tumor cells. Other benefits of a surgical removal of medulloblastoma include a histologic confirmation of the tumor. The spread to the subarachnoid space can be assessed during the procedure. The normal pathway of CSF drainage can be re-established during the procedure [2, 4, 6].

Radiation therapy

This therapy involves the use of high energy beams to kill cancer cells. Local recurrence of the tumor is associated with low dose of radiation therapy at the primary site. Adverse effect of radiation therapy to children receiving the treatment may include dysfunction of the endocrine organs, lower IQ score, abnormalities in the behavior and mental status and development of secondary neoplasms [2, 4, 6].

Chemotherapy

Chemotherapy utilizes antineoplastic drugs to eliminate or inhibit the growth of cancer cells. This therapy may be done in combination with radiation therapy and surgery. The combination of drugs to be used and the cycles the patient receives depends on the progression of the condition. Side effects associated with chemotherapy include disturbances in the gastrointestinal system, ototoxicity, liver toxicity, renal toxicity and pulmonary fibrosis [2, 4, 6].

Prognosis and Life Expectancy

The age of the patient when he is diagnosed with a medulloblastoma affects the prognosis. The 5-year survival rate for children with this condition is currently at 70-80%. Infants who have the same tumor have a lower survival rate of around 30-50%. Adults who have developed a medulloblastoma have a 5-year survival rate of around 57-60% and a 10-year rate of 44%. The outcome of the treatment is affected by several factors such as the age of the patient at the time of the diagnosis, the size of the mass and the presence of tumor metastasis.

References

• WebMD. (2015, May 28). Medulloblastoma. Retrieved from WebMD: http://www.webmd.com/cancer/brain-cancer/medulloblastoma
• Jallo, G. I. (2014, October 16). Medulloblastoma. Retrieved from Medscape: http://emedicine.medscape.com/article/1181219-overview
• American Brain Tumor Association. (2014). Medulloblastoma. Retrieved from American Brain Tumor Association: http://www.abta.org/brain-tumor-information/types-of-tumors/medulloblastoma.html?referrer=https://www.google.co.nz/
• Macmillan Cancer Support. (2015). Medulloblastoma. Retrieved from Macmillan Cancer Support: https://www.macmillan.org.uk/information-and-support/brain-tumours/understanding-cancer/types-of-brain-tumour/medulloblastoma.html
• Pediatric Oncology Education Materials. (2008). Staging. Retrieved from Pediatric Oncology Education Materials: http://www.pedsoncologyeducation.com/medulloblastoma_staging.asp
• Boston’s Children Hospital. (2015). Medulloblastoma Symptoms & Causes. Retrieved from Boston’s Children Hospital: http://www.childrenshospital.org/conditions-and-treatments/conditions/medulloblastoma/symptoms-and-causes

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