Tumour Classification 1
How are brain tumours generally classified?
Patients can easily be confused by different terms sometimes used
interchangeably:
- Slow growing = benign = Grade 1 = pilocytic or juvenile = low
grade
- Rapidly growing = malignant = Grade 3 or 4 = glioblastoma = high
grade
- Somewhere in between = aggressive = Grade 2 or 3 = anaplastic =
medium grade
Glioblastoma
What is a glioblastoma?
This is the name given to a highly malignant
astrocytoma. The full name is glioblastoma multiforme or grade 4
astrocytoma. The name is less often used today as it has been
superseded by simply...malignant glioma. Indeed, the 4 tier system of
classifying these primary brain tumours has been replaced by the more
simple 3 tier system, or WHO classification. In this system, gliomas
can be either low grade, anaplastic or malignant.
What is an Acoustic Neuroma?
This is a very specific type of brain
tumour that accounts for 8% of all intracranial tumours. It really
should be called a vestibular schwannoma, as it neither arises from the
acoustic nerve, nor is it a neuroma. They are more common in females,
usually present with unilateral hearing loss or ringing in the ear, and
are mostly slow growing (approx. 1 mm per year). The prognosis is
usually very good when they are treated. If the patient is opposed to
surgery or is unfit for surgery then watching them for a while is not
unreasonable. If the growth rate is slow then they may never get big
enough to cause any other problem apart from hearing loss. If, however,
the tumour grows bigger while being followed, then surgery and
radiotherapy are riskier. The major risk from surgery is hearing loss,
which is not that disturbing in most patients who present with hearing
loss, and facial nerve damage, which causes asymmetry of the face. The
risk is directly related to the size of the tumour and the skill of the
operating surgeon. Radiosurgery has been successful in arresting the
growth of these tumours, but may only have a limited effect and may
cause delayed damage to the facial nerve. If the tumour is incompletely
removed it will recur. Other complications of surgery include, spinal
fluid leak, chronic headache and persistent ringing in the ear if the
damaged acoustic nerve is preserved. [see Brain Tumours - Series 5]
What is an Astrocytoma?
These grow from astrocytes, which make up the
main substance or bulk of the brain. They are the most common primary
brain tumour and can be very slowly or very rapidly growing. They have
been given many different names and classified in many different ways.
Rare types of astrocytomas (and their grade) are:
- Pleomorphic xanthoastrocytoma (PXA) = low grade
- Collision tumour = high grade
- mixed oligoastrocytoma = medium grade
- optic glioma = usually low grade
Sometimes astrocytomas are clearly demarcated from normal brain tissue
but unfortunately, in the majority of cases they spread fine, invasive
"tentacles" throughout the surrounding tissue, making total removal
very difficult. If the tumour is very fast growing (malignant) then
even if only one cell remains after surgery, the tumour can regrow.
Even low grade astrocytomas can regrow. This invariably happens in
adults but thankfully not so commonly in children.
What is an Oligodendroglioma?
These are rare forms of gliomas that grow
from oligodendroglial cells, or the "connective tissue" of the brain.
These are usually slow growing but more aggressive when seen in adults.
These brain tumours contain little specks of calcium. They may do
better with chemotherapy before radiotherapy. They may also be treated
with radical surgery, with long-term survival.
What is an Ependymoma?
These are more commonly seen in children, but
also occur in adults in a very slow growing form (subependymoma). They
are traditionally insensitive to chemotherapy and only partially
sensitive to radiotherapy. Radical and complete removal by surgery is
associated with the best outcome but the patient may suffer in
postoperative neurological problems.
What is a Ganglioglioma?
These are a low grade brain tumour seen in
children. They can be removed by surgery but sometimes even this may
not be necessary.
What is a Central Neurocytoma?
These brain tumours are low grade and
often confused with an oligodendroglioma. They may be cured with
radical surgery.
What is a Pituitary Adenoma?
A pituitary adenoma is a specific type of
brain tumour that arises from the pituitary gland. This gland is
situated directly behind the nose, under the frontal lobes of the
brain. It controls the regulation of many different hormones and is
vital to life. These adenomas secrete hormones, some active others not,
and symptoms depend on the type of hormone secreted. The most common
hormone produced by one of these tumours is PROLACTIN which can cause
impotence in males and infertility in females. The next most common is
an INACTIVE HORMONE that usually causes symptoms related to the size of
the tumour and the pressure it causes on surrounding structures such as
the visual pathways, the normal pituitary gland and the brain itself.
The next most common adenoma produces GROWTH HORMONE which can cause
excessive growth in children or acromegaly in adults. The least common
hormone secreted by a pituitary adenoma is ACTH which causes Cushing's
Disease. Most adenomas are benign and can be cured with either surgery,
chemotherapy, radiotherapy or combinations of all 3 treatments.
What is a brainstem tumour?
This simply refers to the location of the
tumour. These tumours can be of any histological type. They can be
either outside the brainstem growing in or inside the brainstem growing
out. However, because of their precarious location in or around the
brainstem, they are often incorrectly lumped together under one name.
This is often confusing for patients because some types can be removed
and cured while others shouldn't even have a biopsy!
What is a Brainstem glioma?
These are primary brain tumours that arise
from glial cells within the brainstem. It is arguably the most vital
part of the brain in that it is the relay station for all messages that
travel between the brain proper and the spinal cord. It also contains
the centre that controls breathing, swallowing, eye movement, facial
expression, and many more important functions. Previously, tumours in
this region were all considered "inoperable". Now, most paediatric
neurosurgeons realise that to lump all brainstem tumours together under
the one heading is inaccurate.
Which brainstem tumours are generally operable?
Patients who have
brainstem tumours that are focal, cystic and/or located in the lower
brainstem (medulla) should be given the option of surgery.
Which brainstem tumours are generally inoperable?
Brainstem tumours
that uniformly expand the middle of the brainstem (pons) should not
generally be operated on or even be biopsied.
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