Medulloblastoma / PNET
A medulloblastoma / PNET is a malignant (cancer) tumour formed from primitive or poorly developed brain cells.
Most of these tumours originate in the lower back part of the brain (called the cerebellum) and are called medulloblastomas.
When they occur in other parts of the brain they are called PNETs (Primitive Neuro Ectodermal Tumours). If a PNET occurs in the area of the brain called the pineal gland, then the PNET is known as a pineoblastoma. All PNETs can sometimes spread (disseminate or metastasise) to the spinal cord through the cerebrospinal fluid. They rarely spread to other organs of the body.
Who gets medulloblastoma / PNET?
Less than 90 children a year develop medulloblastoma or PNET in the UK. However, it is still the most common malignant brain tumour in children, 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. They can also be found in adults but are extremely rare.
Like most brain tumours the cause of medulloblastoma or PNET is usually unknown.
Signs and symptoms
The symptoms are usually due to increased pressure in the head (raised intracranial pressure). Symptoms include:
- nausea and vomiting (most common)
- lethargy and irritability
- difficulty with tasks like handwriting
- gradual decline in school work
- changes in personality and behaviour
- abnormal gait (the way the child walks).
If the tumour spreads to the spinal cord, the signs and symptoms may include:
- back pain
- difficulty walking
- problems with bowel and bladder control.
Tests / investigations
We will need to carry out some tests to find out as much as possible about the type, position and size of the tumour. This is will help us to decide on the best treatment for your child. These tests include:
- CT scan – it is likely that a CT scan of your child’s brain was carried out at your local hospital. Although MRI scans are usually the best way of seeing the tumour and the effects of treatment, sometimes CT scans are also used.
- MRI scan – this scan allows us to see the brain and spine in great detail and is used regularly to diagnose and follow the effect treatment is having on your child’s tumour.
- Lumbar puncture – this is carried out under general anaesthetic about 14 days after surgery, to look for any malignant cells in the cerebrospinal fluid.
Staging is a measure of how far the tumour has spread beyond its original site. The staging system we use for medulloblastoma / PNET is:
- M0: No evidence of metastases.
- M1: Tumour cells found in cerebrospinal fluid (lumbar puncture cerebrospinal fluid test).
- M2: Tumour spread beyond original site but still in the brain.
- M3: Tumour deposits (seeds) in the spine that are easily seen on MRI scan.
- M4: Tumour spread to areas outside the central nervous system (brain and spine).