The brain is an elaborately designed organ that has well organized tissues and nerves. It is the brain that runs the entire body, controls its vital functions and determines our personality. It is encased in by the hard skull bones and the layers (meninges), to protect it from damage. There is also a cerebrospinal fluid that flows throughout the spaces in the meninges and the spaces (also called ventricles) in the brain, as well.
The three chief parts of the brain manage diverse activities.
- The Cerebrum: The cerebrum processes the information coming in from the environment, via our senses and tells us how to respond. It regulates our cognitive skills like thinking, learning, speech, feelings and emotions. The cerebrum is separated into two, the right & left cerebral hemispheres. The right hemisphere is in control of the body’s left side and the left hemisphere is in control of the body’s right side.
- The Cerebellum: The cerebellum is that lower part of the brain, controlling the body’s balance for walking, standing, and other multipart actions.
- The Brain Stem: The brain stem is the part that connects the brain to the spinal cord. It controls vital body functions like breathing, body temperature and blood pressure.
What is a medulloblastoma ?
Medulloblastoma is a tumour affecting the cerebellum — the lower, rear part of the brain. Medulloblastomas start from the neuroectodermal cells (that is the primitive, embryonal nerve cells) in the cerebellum. They are speedily-growing tumours, which can easily extend through the cerebrospinal fluid (CSF) pathways.
Where does medulloblastoma occur ?
Medulloblastomas occur a great deal more in children than in adults. They are part of a class of tumours called primitive neuroectodermal tumors (PNETs) that can also start in other parts of the central nervous system.
What are the causes of medulloblastoma ?
The causes of medulloblastoma are still unknown, but strides are being made in understanding the biology of the disease. There is an alteration in certain genes and chromosomes (the genetic blueprint of the cell) that contributes to this disease. Some of the pediatric medulloblastomas have an alteration on chromosome 17. Comparable changes can be seen on chromosomes 1, 7, 8, 9, 10q and 11 chromosomes. Certain genetic syndromes also have higher incidence of this disease. Some people afflicted by Gorlin’s Syndrome could develop medulloblastoma. (Gorlin’s Syndrome is a combination of increase in incidence of basal cell carcinomas with other specific conditions.). This may be due to alterations on a gene called PTCH which may be the common connecting factor. Similarly, Turcot and Li-Fraumeni Syndrome also could have higher incidence of medulloblastomas.
What are the types of medulloblastomas ?
It is important to note that though medulloblastoma has been divided into numerous histopathologic variants, because of their variable appearance under the microscope, all the variants are still treated the same clinically. Classifying these tumours into histopathologic variants may come in handy for targeted therapies, in the future.
The histopathologic variants of medulloblastoma are mentioned below.
- Classic medulloblastoma : This is the usual picture of medulloblastoma, seen in both pediatric and adult tumours.
- Desmoplastic modular medulloblastoma : A picture of a dense connective tissue will be seen, spreading apart the tumour islands.
- Large-cell or anaplastic medulloblastoma : Large or anaplastic tumour cells will be seen.
- Medulloblastoma with neuroblastic or neuronal differentiation : Tumour cells have resemblance to atypical nerve cells.
- Medulloblastoma with glial differentiation : Tumour cells resemble supportive, glial brain cells.
- Medullomyoblastoma & melanotic medulloblastoma include the rarer variants of tumour.
What are the clinical features of medulloblastoma ?
Symptoms of the tumour depend on the nerves and brain structures affected by the tumour. Since medulloblastomas appear in the cerebellum, the controller of balance and movement, there will be problems with dizziness and coordination. Tumours growing in size may block the normal flow of cerebrospinal fluid. This will result in hydrocephalus — or the building up of cerebrospinal fluid in one of the brain cavities. The pressure of this fluid build-up generates the tumour’s symptoms: Morning headaches, nausea, vomiting and lethargy.
There could be a change in walking patterns and problems in vision.
In small infants, symptoms can be less obvious and include intermittent vomiting, failure to thrive, weight loss, an enlarging head and an inability to raise the eyes upward.
How is medulloblastoma diagnosed ?
- A complete physical examination of the body is mandatory.
- Imaging Tests: Important diagnostic tests include MRI Scans or PET Scans. Magnetic Resonance Imaging (MRI), both with and without a contrast dye & Computed Tomography (CT) Scans are the imaging tests used most often for diagnosis of brain diseases. CT scan and /or MRI should be carried out to provide the exact anatomical information of the tumour such as its extent and measurements. Doctors can then view, assess and judge the cancer and determine how far it has progressed or spread.
Magnetic Resonance Spectroscopy (MRS): This may be used to determine if what is seen on the scan is growing, live tumour as opposed to radiation effects or non-growing tissue.
Magnetic Resonance Angiography (MRA): This specialized MRI is done to analyze the blood vessels in the brain. This is extremely useful before surgery to help the surgeon plan operations. - Biopsy : Removed tissue examined under a microscope by a pathologist is necessary. A histological study of the biopsy, under the microscope is required to confirm the cancer diagnosis. It could be either by a stereotactic (needle) biopsy or a surgical and open biopsy (craniotomy).
How are medulloblastomas treated ?
Firstly, the tumours have to be staged. This has to be done both locally and systemically. There are different treatments required at different stages of disease, and the treatment plan will be decided by a team of doctors of oncologists and a neurosurgeon. Moreover, age at the time of occurrence of medulloblastoma and prognostic factors (such as metastasis and residual tumour) both influence treatment strategies.
The current treatment of medulloblastomas involves surgically removing as much tumour as possible, followed by craniospinal (brain and spine) radiation and/or chemotherapy.
- Surgery : Removing as much tumour as possible is the most important step in treating medulloblastoma. MRI scanning combined with computer-aided navigation tools help the neurosurgeon map the exact tumour location before the operation, and track its removal during the procedure. However, sometimes, the tumour may not be completely operable.
- Radiation Therapy : A cancer treatment that utilizes high-energy x-rays or basically radiation to eradicate cancer cells. Radiation therapy has to be used post surgery to kill any remaining cancer cells. It is an important “next-step” because microscopic tumour cells can remain in the surrounding brain tissue even after surgery has successfully removed the entire visible tumour and can cause tumour re-growth.
- Chemotherapy : Chemotherapy is now a standard part of treatment for children with medulloblastoma. It is a cancer treatment that uses either drugs or chemical substances (hence the name chemotherapy) to kill cancer cells and prevent them from dividing. For children with medulloblastoma, chemotherapy is used to reduce the risk of tumour cells spreading through the spinal fluid. For adults, this benefit is not quite as clear since their tumours tend to re-grow in the cerebellum. Because different drugs are effective during different phases of a cell’s life cycle, a combination of drugs may be given. The combination increases the likelihood of more tumour cells being destroyed.
What is the care to be taken after the removal of a medulloblastoma ?
Metastatic diagnostic workup and monitoring post-treatment for aggressive or disseminated medulloblastomas includes imaging and scanning of the limbs, thorax, chest, retroperitoneum, and abdomen with radiography, MRI or CT scans.
MRI scanning of the brain will be done every 2-3 months and spinal MRI every 4-6 months for the first two years following surgery. The scans help determine the effectiveness of treatment, and are used to monitor for early evidence of a recurrence.
Neuropsychological testing before treatment is important for follow-up evaluations. If learning difficulties arise after treatment, these baseline results need to be there for comparison. Children should be watchfully monitored for long-term cognitive problems, if and when they develop. They then will need rapid, early and effective learning support and aids.
In addition, if the need arises, consultation from an endocrinologist (a specialist in hormones) or an oncologist (a cancer specialist) will be advised. Rehabilitation as well as special education programs will be needed for children to attend school.
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Disclaimer: The content provided here is meant for general informational purposes only and hence SHOULD NOT be relied upon as a substitute for sound professional medical advice, care or evaluation by a qualified doctor/physician or other relevantly qualified healthcare provider.
