Sorting brain tumours into different types
There are
nearly 100 different types of brain tumours. They are generally named after the
type of cell they developed from. Most brain tumours develop from the cells
that support the nerve cells of the brain called glial cells. A tumour of glial
cells is a glioma.
Brain
tumours can also be named after the area of the brain they are growing in. A
tumour of the pituitary gland is called a pituitary adenoma. A tumour developed
from the covering of the brain (the meninges) is called a meningioma. Tumours
growing from the nerves entering the brain are called neuromas. An acoustic
neuroma is a tumour growing on the nerve that controls hearing.
Brain tumour grade - benign or malignant
Brain
tumours are put into groups according to how quickly they are likely to grow.
There are 4 groups, called grades 1 to 4. The cells are examined under a
microscope. The more normal they look, the more slowly the brain tumour is
likely to develop and the lower the grade. The more abnormal the cells look,
the more quickly the brain tumour is likely to grow and the higher the grade.
Low grade gliomas (grade 1 and grade 2) are the slowest
growing brain tumours.
You may
have been told you have a benign tumour or a malignant tumour. As a rule of
thumb, low grade tumours are regarded as benign and high grade as malignant. By
benign, we generally mean the following.
·
The tumour is relatively slow growing
·
It is less likely to come back if it is completely removed
·
It is not likely to spread to other parts of the brain or spinal
cord
·
It may just need surgery and not radiotherapy or chemotherapy as
well
By
malignant, we generally mean the following.
·
The tumour is relatively fast growing
·
It is likely to come back after surgery, even if completely
removed
·
It may spread to other parts of the brain or spinal cord
·
It can't just be treated with surgery and will need radiotherapy
or chemotherapy to try to stop it from coming back
With other
types of cancer, these black and white explanations of benign and malignant
work well. But with brain tumours, there are a lot of grey areas. Some low
grade astrocytomas can spread to other parts of the brain
or spinal cord. Radiotherapy and chemotherapy are sometimes used to treat
benign tumours. Even a slow growing tumour can cause serious symptoms and be
life threatening if it is in a crucial part of the brain. So, it is important
to ask your specialist to explain your own situation to you fully and simply.
Gliomas
About half
of all primary brain tumours are gliomas. There are 3 main types of glioma - astrocytoma,ependymoma and oligodendroglioma.
A fourth type, mixed glioma, is a
mixture of the other types. Your doctor will use the grade of your glioma to
decide your treatment and the likely outcome. But the position of the tumour is
also very important. For example, brain
stem gliomas are particularly
difficult to treat, whatever their grade. The brain stem is a very complicated
and delicate part of the brain and completely removing the tumour is not likely
to be possible. Unfortunately, high doses of radiotherapyare
not recommended either as this may cause too much damage to the normal brain
stem.
Astrocytomas (including glioblastoma multiforme)
Astrocytomas
are the most common type of glioma in both adults and children. They develop
from cells called astrocytes. The astrocytes are the 'bricks and mortar' of the
brain that support the nerve cells (neurones). They probably do other things
too (but we don't know what as yet). Astrocytomas can be slow (low grade) or
fast growing (high grade). Some are very localised (focal). This means it is
easy to see the border between tumour and normal brain tissue on a scan or
during an operation. Focal astrocytomas are more often diagnosed in children
and are not common in adults. Other astrocytomas are called diffuse. These do
not have a clear boundary between the tumour and normal brain tissue.
Anaplastic
astrocytoma (also called grade 3 astrocytoma) and glioblastoma multiforme (GBM
or grade 4 astrocytoma) are the most common type of brain tumour in
adults. These are malignant (high grade) brain gliomas. They can sometimes
spread to other parts of the brain.
Ependymomas
About 1 in
20 brain tumours (5%) is an ependymoma. These develop from cells called
ependymal cells. These cells line the fluid filled areas of the brain (the
ventricles) and spinal cord.
Their job is to repair any damaged nerve tissue. Most ependymomas are diagnosed
in children or young adults. They can be high or low grade, but the cells'
appearance under a microscope does not always fit with their behaviour. So the
grade may not tell you much. Sometimes ependymomas can spread within the
central nervous system, via the fluid that circulates round the brain and
spinal cord, but this is not common.
Oligodendrogliomas
About 1 in
20 brain tumours (5%) is an oligodendroglioma. These develop from cells called
oligodendrocytes. These cells make a white fatty substance that covers nerves,
called myelin. It helps the nerve signals (impulses) to travel along the nerves
more quickly. Oligodendrogliomas are most often found in the forebrain, in the temporal or frontal
lobes. They can be fast or slow growing. They are most likely to be diagnosed
in adults, although they do occur in young children. Sometimes this tumour can
spread within the central nervous system, in the fluid that circulates round
the brain and spinal cord.
Mixed gliomas
These are
gliomas that are a mixture of 2 or even 3 of the different types of glioma. The
cell types can be different grades too. Your doctor will look at the different
types of glioma cells and give you the treatment that is appropriate for the
most aggressive cell type in your brain tumour.
Acoustic neuromas
Acoustic
neuromas grow in the nerve that runs from the ears to the brain and controls
hearing and balance. They are nearly always slow growing, do not spread and are
thought of as benign brain tumours. Often, they have been there a long time by
the time they are diagnosed. They are found most often in older people. Loss of
hearing in one ear can be a sign of acoustic neuroma. Rarely, they are
associated with one form of a genetic condition called neurofibromatosis type 2 (NF 2). In these cases, they
are usually diagnosed at a much younger age, can be on both sides (bilateral)
and people affected may also develop meningiomas.
Craniopharyngiomas
Craniopharyngiomas
are tumours that tend to grow near the base of the brain, just above the pituitary gland. They are most often
diagnosed in children, teenagers and young adults. They do not usually spread,
but are near important structures in the brain and can cause problems as they
grow. They can cause changes in hormone levels and problems with eyesight.
Children with craniopharyngioma can have weight gain and growth problems.
Only 2 out
of every 100 brain tumours (2%) are haemangioblastomas. They grow from blood
vessel cells. They are very slow growing and do not spread. But they can grow
in the brain stem and then they are very difficult to
treat. Sometimes these brain tumours can be part of a rare syndrome called von
Hippel Lindau syndrome (vHL),
which runs in families. People with vHL who develop haemangioblastoma may have
more than one. Not everyone with vHL will get haemangioblastomas - the
condition behaves differently in different people.
Lymphomas
Sometimes
lymphoma can start in the brain. This is called primary cerebral lymphoma or
primary central nervous system (CNS) lymphoma. Most are a type of lymphoma
called diffuse large B cell non Hodgkin's lymphoma. People who have poor
immunity due to AIDS or due to medicines taken after an organ transplant are
more likely to develop cerebral lymphoma than other people in the population.
Lymphoma is
a cancer of the lymphatic system.
These tumours are treated differently to other types of brain tumour. There is
a section about non Hodgkin's
lymphoma on this website,
including treatment information.
Meningiomas
About 1 in
4 brain tumours in adults (25%) is a meningioma. They are more common in older
people and in women. These tumours start in the tissues covering the brain
(membranes). They are most often found in the forebrain or hindbrain.
They are usually benign (not cancerous).
Some
meningiomas are atypical. This means that they behave more aggressively than
normally expected for meningiomas. They can grow into surrounding brain tissue
and may come back after they have been removed.
Meningioma
symptoms vary a lot, depending on where in the brain they are growing.
Germ cell tumours
A germ cell
tumour grows from primitive developing cells that form in the embryo and
develop into the reproductive system. Most occur outside the brain, in the
chest or abdomen but they can occur in the brain. They are most commonly found
in the pineal and suprasellar areas. Germ cell tumours account for about 2 out
of 100 (2%) of all brain tumours in children. Around half of these tumours occur
in young people between 10 and 20 years old.
Germ cell
tumours sometimes produce chemicals that can be tested for in the blood - AFP
and HCG. So sometimes these tumours can be diagnosed with a blood test. They
are often picked up when they are still small, because they can block the
circulation of fluid around the brain and tend to cause symptoms early on.
Pineal region tumours
The pineal
gland is in the middle of the brain, just behind the top of the brain stem. It
makes the hormone melatonin. Pineal tumours are rare and account for only 1 in
every 100 brain tumours (1%). Several different types of tumours can grow in
the pineal region, including gliomas.
The most common types are germ
cell tumours.
Pituitary tumours
About 1 in
10 brain tumours (10%) are in the pituitary
gland. They are more common in older people. The pituitary gland is attached to
the underside of the brain. It lies in a small hollow in the skull, just behind
the eyes. It controls many body functions by making and releasing chemical messengers
(hormones) into the bloodstream. The pituitary hormones travel in the blood to
other glands in the body, such as the thyroid, ovaries and testicles. The
pituitary hormones control amounts of other hormones that these glands release
into the blood.
Most
pituitary tumours develop from the gland tissue and are called adenomas. They
are nearly always benign - they grow slowly and do not spread. Pituitary
tumours can often cause quite odd symptoms because the tumour cells make too
much of one of the pituitary hormones.
Primitive neuroectodermal tumours (PNETs)
These
tumours develop from cells that are left over from the earliest development of
the body in the womb. Normally, these cells are harmless. But sometimes they
can become cancerous.
Medulloblastoma
is the commonest type of PNET. These grow in the hindbrain They are the second
most common brain tumour in children, but the commonest malignant (high grade)
childhood brain tumour. Medulloblastomas are also diagnosed in young
adults.These tumours can be fast growing and can spread to other parts of the
brain and to the spinal cord through the cerebrospinal fluid (CSF).
Spinal cord tumours
Up to 1 in
5 central nervous system tumours (20%) are in the spinal cord. There are a few
different types. The success of treatment depends on the type of spinal cord
tumour.
Meningiomas and neurofibromas are the commonest
types seen in adults. They grow outside the spinal cord, but press on it. Astrocytomas and ependymomas grow in the spinal cord tissue itself.
These are the commonest types in children. Another rare type is called a chordoma.
Tumours
growing in the bones of the spine can press on the spinal cord and cause
similar symptoms to spinal cord tumours. In adults, these are usually secondary cancers that have spread into the spinal bones from somewhere
else in the body. For example, the lungs, prostate, kidney or the breast. Lymphomas and myeloma can also spread to the spine.
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