What is a brainstem glioma?
Gliomas are a large, diverse group of brain tumours that develop from glial cells, which have a range of supportive roles within the brain. Brainstem gliomas develop in the brain stem that connects the base of the brain to the spinal cord, just above the back of the neck. The brain stem consists of three parts:
The midbrain, which develops into its stem form out of the middle of the brain.
The pons, which is found between the midbrain and the medulla oblongata. Most brainstem gliomas arise in this particular part of the brain stem.
The medulla oblongata, formed by the top of the spinal cord spreading out at the base of the brain.
What does the brain stem do?
The brain stem acts as the main highway of communication between the brain, the spinal cord, and hence the rest of the body. Most of the nerves that originate in the brain and spread out into the body pass through the brain stem.
The brain stem also influences bodily functions that happen mainly subconsciously via the autonomic nervous system such as alertness, breathing, swallowing, blood pressure and heart rate.
Are brain stem glioma tumours benign or cancerous?
Any tumour affecting the brain stem is likely to cause symptoms that cannot be considered “benign”, so tumours tend to be referred to as low-grade or high-grade. Low-grade tumours are a slow-growing form of cancer, whilst high-grade tumours are an aggressive form of cancer.
In children, brain stem gliomas can be low-grade (slow growing, grades 1 and 2) or high-grade (fast growing, grades 3 and 4), but unfortunately they are most often high-grade.
In adults, brain stem gliomas tend to be low-grade and hence classified as grade 1 or grade 2. Grade 2 gliomas may sometimes transform to a higher grade over a number of years.
What types of brainstem glioma are there?
Brainstem gliomas are classified into a number of different types, with names primarily reflecting their position and spread, as well as the types of cells seen when a tumour sample is viewed through a microscope (histology).
Diffuse brainstem astrocytoma
“Diffuse” means that the tumour has spread out through the brain stem, in amongst healthy cells. Astrocytoma is a type of glioma that most closely resembles astrocyte cells.
- Diffuse astrocytoma in the brain stem can be grade 2 or grade 3.
- A grade 4 diffuse brainstem glioma is the most common form. It is usually referred to as a diffuse intrinsic pontine glioma (DIPG), despite new classifications published by the World Health Organisation (WHO) in 2016 meaning that it is officially known as a diffuse midline glioma.
Focal brainstem glioma
About 20% of brainstem tumours are focal, meaning that they are localised (focused) in one area of the brain stem, usually the midbrain or medulla rather than the pons.
They tend to be low-grade and easier to target with treatments such as surgery and radiotherapy than diffuse glioma.
- Fibrillary astrocytoma, grade 2
- Pilocytic astrocytoma, grade 1
- Ganglioglioma, usually grade 1 but occasionally grade 3
Tectal plate glioma
Tectal plate gliomas are a form of focal brainstem glioma that arises in the tectal plate region of the brain stem. The tectal plate controls hearing and sight reflexes.
- Usually a low-grade astrocytoma, grade 1 or 2
Dorsally exophytic glioma
Exophytic gliomas are focal brainstem tumours that project into the fourth ventricle or cerebellopontine angles of the brain. They tend to cause hydrocephalus (a build-up of fluid in the brain) because the tumour blocks the flow of cerebrospinal fluid (CSF).
Neurofibromatosis 1 (NF1) associated brainstem glioma
Up to 9% of patients diagnosed with the genetic condition neurofibromatosis 1 may develop a brainstem glioma.
- Most often develop in the medulla
- Are focal in appearance, and rarely grow or progress to a higher grade
Cervicomedullary brainstem gliomas
A group of brainstem gliomas of different types, but classified by their position.
- Brainstem gliomas that have grown downwards into the cervicomedullary area
- Upper cervical cord intramedullary spinal cord tumours that have grown upwards into this area of the brainstem.
What is the prognosis for brainstem gliomas?
As this is a very diverse group of tumours, prognosis for the group as a whole is not available because survival times vary hugely. The prognosis for a brainstem glioma is dependent upon a range of factors, primarily the location and grade of the tumour.
A low-grade focal brainstem glioma usually has a prognosis of many years, extended by the help of successful surgery to remove as much of the tumour as possible.
The overall survival for pontine gliomas is 10% at 5 years.
The prognosis for a grade 4 DIPG (diffuse midline glioma) may be as short as a few months, and 90-100% patients die within 2 years of diagnosis. This is why so much research is focused on finding a cure for this incredibly challenging form of brain tumour.
What are the symptoms of brainstem glioma tumours?
Symptoms will depend upon the exact location of the tumour, and hence the areas of the brain and nervous system that it is affecting. Usually patients will present with more than one of the following, and sometimes the symptoms can worsen very quickly (in a matter of days):
- Headaches, often worse in the morning or after lying down, due to hydrocephalus: the build-up of CSF fluid in the brain
- Loss of full control of bodily movements (ataxia and long tract signs): for example problems with walking, using the hands, or what appears to be general clumsiness
- Problems with nerve signals in the face including eyes (cranial nerve palsies): for example a crooked smile, a drooping eyelid or an upward gaze
- Difficulties with chewing or swallowing
- Slurred speech or other difficulties with speaking
- Vomiting, for example soon after waking up in the morning or after doing strenuous exercise.
How is a brainstem glioma tumour diagnosed?
The most reliable way to diagnose any kind of brain tumour is initially by an MRI scan and then by taking a biopsy (a small sample of the tumour, removed during neurosurgery) for analysis in a laboratory.
How common are brainstem glioma tumours?
Brainstem gliomas are most common in children between 7 and 9 years of age.
- Almost 11% of all childhood brain and central nervous system tumours are brain stem gliomas.
- They account for around 25% of all the tumours diagnosed in the posterior fossa area of the brain, which is at the back and base of the head and includes the brain stem.
Brainstem gliomas can also be diagnosed in adults, typically young adults under 40 years of age, and at this stage of life tend to be low-grade (Grade 1 or 2).
They account for around 2% of primary adult brain tumours, “primary” meaning tumours that arise in the brain rather than metastasising from another form of cancer.
What causes a brainstem glioma tumour?
The cause of most brainstem gliomas is not known, so unfortunately there are no proven ways to prevent them from occurring.
Some brainstem gliomas arise as a result of having a genetic condition called neurofibromatosis 1. Patients with this condition will have specialists in neurofibromatosis caring for them alongside their neuro-oncology team.
Treatment options for brainstem glioma
Most of these tumours develop in the pons area of the brain stem, making them very challenging to treat using surgery. Sometimes part of a focal brainstem glioma may be able to be removed, but often surgery for a brainstem glioma is considered too difficult to undertake because of the risk of side effects.
Radiotherapy needs to be very carefully targeted in order to minimise damage to the brainstem, so is likely to be a form of stereotactic radiotherapy such as proton beam therapy.
Chemotherapy is the most common form of treatment for most forms of brainstem glioma, and the drugs used will depend upon the exact type of glioma that is diagnosed.
Patients may be offered a cerebral spinal fluid (CSF) shunt in order to reduce the effects of hydrocephalus, if this is present. The shunt is inserted during a neurosurgical operation and works to drain excess fluid away from the brain.
There are many researchers looking for a cure for DIPG, the most aggressive form of brainstem glioma, so new treatments may be available to some brainstem glioma patients in the context of clinical trials.
How will we find a cure for brain stem glioma tumours?
Research we are funding across all of our dedicated Research Centres will help lead towards finding a cure for a wide range of brain tumours.
Pioneering research at our Brain Tumour Research Centre at Queen Mary University of London is focused on using glioblastoma multiforme (GBM) stem cells to help develop unique, patient-specific treatments. GBMs are the most aggressive type of glioma brain tumour in adults. Findings are expected to translate into other types of adult and paediatric brain tumours.
Our team at the University of Plymouth Low-Grade Brain Tumour Research Centre are researching a number of molecular pathways that influence immune system function, tumour metabolism and tumour growth in a range of low-grade brain tumours in children and adults. This includes how gliomas begin, and how they transform from low-grade to high-grade.
The team of research and clinical experts in our Research Centre at Imperial College, London are studying the way in which the ketogenic diet works in brain tumours including DIPG. Their work on drugs that reduce levels of arginine, an amino acid in the blood, may also have the potential to influence a wide range of brain tumours.
Scientists at our Research Centre in the University of Portsmouth are studying mitochondria, exploring ways to ‘shut down’ these ‘batteries’ that supply energy to brain tumours.
We also fund BRAIN UK at Southampton University, the country’s only national tissue bank registry providing crucial access to brain tumour samples for researchers from all clinical neuroscience centres in the UK, effectively covering about 90% of the UK population, and an essential component in the fight to find a cure for all types of brain tumours.