Medulloblastoma

Definition

Definition of Medulloblastoma
Medulloblastoma is a highly malignant primary brain tumor that originates in the cerebellum or posterior fossa.

Previously, medulloblastomas were thought to represent a subset of primitive neuroectodermal tumor (PNET) of the posterior fossa. However, gene expression profiling has shown that medulloblastomas have a distinct molecular profile and are distinct from other PNET tumors.

Tumors that originate in the cerebellum are referred to as infratentorial because they occur below the tentorium, a thick membrane that separates the cerebral hemispheres of the brain from the cerebellum. Another term for medulloblastoma is infratentorial PNET. Medulloblastoma is the most common PNET originating in the brain.

Symptoms

Symptoms of Medulloblastoma
The first symptoms of any brain tumour are usually due to increased pressure within the skull (raised intracranial pressure).

This may be caused by a blockage in the ventricles (fluid-filled spaces in the brain), which leads to a build-up of CSF. The increased pressure can also be caused by swelling around the tumour itself.

Raised intracranial pressure can cause headaches, sickness (vomiting|) and sight problems. Vomiting is common first thing in the morning. Children often appear tired, weak and irritable. Changes in personality and behaviour may also be noticed.

As the cerebellum is the part of the brain that controls muscle coordination, a tumour in this area may cause problems with walking. A person may appear to stumble, or walk in an awkward or uncoordinated way. Speech can also be affected, and words may be slurred or muddled.

Other specific symptoms associated with medulloblastoma are nystagmus (jerky eye movements), stiffness in the neck, and muscle weakness. The symptoms that people have will depend on the size and position of the tumour.

Causes

Causes of Medulloblastoma
As with most brain tumours, the cause of medulloblastoma is unknown. Researchers| are trying to discover possible causes.

Diagnosis

Diagnosis of Medulloblastoma
The tumor is distinctive on T1 and T2-weighted MRI with heterogeneous enhancement and typical location adjacent to and extension into the fourth ventricle.

Histologically, the tumor is solid, pink-gray in color, and is well circumscribed. The tumor is very cellular, many mitoses, little cytoplasm, and has the tendency to form clusters and rosettes.

Tests

Tests of Medulloblastoma
Your child's doctors need to find out as much as possible about the type, position and size of the tumour, so they can plan treatment. Your child may have a number of tests and investigations.

A doctor will carry out a thorough examination and test the power and feeling in the arms and legs, and their reflexes.

Your doctor will look into the back of your child's eyes using an ophthalmoscope. They can see if the optic nerve at the back of the eye is swollen. This can be caused by oedema (swelling of the tissues within the brain), which may occur due to an increase in the amount of fluid in the brain.

Treatment

Treatment of Medulloblastoma
Treatment begins with maximal resection of the tumor. The addition of radiation to the entire neuraxis and chemotherapy may increase the disease-free survival. This combination may permit a 5 year survival in more than 80% of cases. The presence of desmoplastic features such as connective tissue formation offers a better prognosis. Prognosis is worse if the child is less than 3 years old, there is an inadequate degree of resection, or if there is any CSF, spinal, supratentorial or systemic spread. Dementia post radiotherapy and chemotherapy is a common outcome appearing two to four years following treatment.

1. Chemotherapy: Chemotherapy is now an important part of treatment for all patients with medulloblastoma. It can significantly reduce risk of recurrence (which is typically fatal). There are a couple of different chemotheraputic regimens for medulloblastoma, but most involve a combination of lomustine, cisplatin, carboplatin, vincristine or cyclophosphamide. In younger patients (less than 3–4 years of age), chemotherapy can delay, or in some cases possibly even eliminate, the need for radiotherapy.
2. Survival: Patients diagnosed with a medulloblastoma or PNET are 50 times more likely to die than a matched member of the general population. The most recent population-based (SEER) 5-year relative survival rates are 69% overall, but 72% in children (1-9 years) and 67% in adults (20+ years). The 20 year survival rate is 51% in children. Children and adults have different survival profiles, with adults faring worse than children only after the 4th year post-diagnosis (after controlling for increased background mortality). Before the 4th year, survival probabilities are nearly identical. Longterm sequalae of standard treatment include hypothalamic-pituitary and thyroid dysfunction and intellectual impairment. The hormonal and intellectual deficits created by these therapies causes significant impairment of the survivors.