What is Medulloblastoma?
Medulloblastoma/PNET is the most common brain tumour of
childhood, representing 20% of all childhood brain tumours. They
are most common in children between the ages of three and eight,
and are slightly more common in boys than girls.
The majority of these tumours arise in what is referred to as
the posterior fossa region of the brain. This area includes the
area at the lower back of the head. Often Medulloblastomas are
referred to as a PNET (Primitive Neuroectodermal tumour). These can
arise in the posterior fossa, but are also common in other regions
of the brain, including the pineal gland and cerebrum.
Medulloblastomas/PNETS have the potential to spread (metastasise)
to the spinal column via the cerebrospinal fluid, the fluid
surrounding the brain and spine. Like other childhood brain
tumours, they rarely spread outside the central nervous system
(brain and spinal cord) to other organs of the body.
Signs & Symptoms
Common symptoms include:
Vomiting (most common), with/out nausea. Commonly occurs in
the morning after wakening
Headaches
Clumsiness
Difficulty with tasks like handwriting
Gradual decline in school performance (impaired
attention)
If there is tumour spread to the spinal cord, the signs and
symptoms may include:
Back pain
Diagnosis
The diagnosis of a Medulloblastoma/PNET is made by the
Neurosurgeon taking a biopsy of the tumour. This is taken when the
Neurosurgeon makes attempts to remove the entire tumour. The exact
location of the tumour is determined by an MRI (Magnetic Resonance
Imaging) of the whole brain and spinal cord which is performed
before surgery. Spinal imaging is necessary to rule out spread of
the disease to the spinal cord. Other tests and investigations that
help assist with staging of the disease include a lumbar puncture
(or spinal tap). This detects the presence of tumour cells in the
cerebrospinal fluid (Refer to section on tests and
investigations).
Treatment
Treatment for childhood Medulloblastoma/PNET begins with
surgery, where all attempts are made at achieving a complete
surgical resection of the tumour, with minimal harm to the
surrounding healthy brain tissue. Surgery alone is non-curative, as
it is necessary to kill the microscopic tumour cells that remain
after surgery, but are not visible on the post-operative MRI scan.
Treatment following surgery usually consists of radiotherapy with
chemotherapy.
Children greater than four (4) years of age who have had a complete
tumour resection, receive a combination of cranio-spinal (brain and
spine) radiation, followed by a four (4) month course of intensive
chemotherapy. Because of the significant effects of radiotherapy on
an infant's developing brain, children less than three years of age
receive high dose chemotherapy immediately following surgery, with
the aim to delay or even obliterate the need for radiation
treatment.
If the Neurosurgeon has been unable to completely remove the
tumour and/or there is evidence of tumour spread to the spinal cord
and/or other areas of the central nervous system, the child is
considered high-risk. Treatment is similar for children who
have had a complete surgical excision, however high-risk patients
receive an additional chemotherapy agent, together with higher
doses of radiation to the brain and spine.
Reduced doses of radiation to the entire brain and spine, has
been a major treatment advance in the treatment of
Medulloblastoma/PNET over the last couple of years. It is aimed at
decreasing the long-term side effects that often result from high
doses of radiation delivered to the brain and spine. The use of
peripheral blood stem cell transplants has contributed to this
advance, enabling the intensity of chemotherapy to be increased,
whilst reducing the dose of radiation that is required to the brain
and spine.
This progress has impacted the overall survival rate of this
disease. Survival rates for children who had a complete removal of
their tumour initial surgery, have risen to 80% survival at 5 years
from diagnosis, compared to 50% and 60% survival rates five years
ago. The treatment of infants continues to be difficult. This is
because of the delay in the ability to deliver radiation to the
entire brain and spine, resulting from the known detrimental
effects it has on the developing brain.
Follow Up Care
After treatment has finished, children visit clinic on a regular
basis, and undergo MRI scans and other investigations throughout
their childhood to detect any possible recurrence. Importantly, all
children attend the Neuro-Oncology Long-Term Effects clinic, where
they are regularly reviewed a by a group of specialists involved in
monitoring the specific long term growth and development needs of
these patients.