|
A brain tumor is
any mass created by an abnormal and uncontrolled
growth of cells either found in the brain (neurons,
glial cells, epithelial cells, myelin producing
cells, etc.) or spread from elsewhere (metastasis).
Brain tumors are usually located in the posterior
third of the brain in childhood and in the anterior
two-thirds of the brain in adulthood.
In the United
States in 2000, it was estimated that there were 16,500 new cases of
brain tumors (brain cancers), which accounted for
1.4% of all
cancers, 2.4% of all cancer deaths, and
20%-25% of pediatric cancers. Ultimately, it is
estimated that there are 13,000 deaths/year as a
result of brain tumors / brain cancers.
Brain Tumor and Differenciation
Brain tumors are either benign or malignant and each has
different brain tumor symptoms.
Benign brain tumors include:
- pituitary adenoma - The diagnosis is generally
entertained either on the basis of visual
difficulties arising from the compression of the
optic nerve by the brain tumor, or on the basis of
manifestations of excess hormone secretion: the
specifics depend on the type of hormone. Brain
tumors
which cause visual difficulty are likety to be
macroadenomas greater than 10 mm in diameter;
tumors less than 10 mm are microadenomas.
- meningioma - The symptoms depend closely on
the exact location of the brain tumor. Hence, a
meningioma compressing the frontal lobe can give
rise to frontal lobe syndrome.
- acoustic neuroma - Associated symptoms are
unilateral sensorineural hearing loss/deafness and
vertigo, while larger brain tumors can compress local
structures, such as the facial nerve, and lead to
local symptoms, such as hydrocephalus.
Malignant brain tumors include:
- glioma (60% of new cases) -
Brain tumor
symptoms of gliomas depend on which part of the
central nervous system is affected. A brain glioma
can cause headaches, nausea and vomiting, and
cranial nerve disorders as a result of increased
intracranial pressure. A glioma of the optic nerve
can cause visual loss. Spinal cord gliomas can
cause pain, weakness or numbness in the
extremities.
Gliomas do not metastasize by the
bloodstream, but they can spread via the
cerebrospinal fluid and cause "drop metastases" to
the spinal cord.
- glioblastoma multiforme (WHO Grade IV glioma)
- Common
brain cancer symptoms of the disease
include seizure, headache, hemiparesis, and
personality change.
Some lesions can
mimic tumors of the central nervous system. These
include tuberculosis of the brain and cerebral
abscess.
Primary
Brain Tumor
Primary brain tumors (primary brain cancers) are those tumors that originate in the brain,
and are named for the cell types from which they
originated. Frequently encountered histologic brain tumor types are glioma, glioblastoma, astrocytoma,
oligodendroglioma, medulloblastoma, meningioma and
neuroglioma. Brain tumors can be benign and are usually,
but not necessarily, localized to a small area. They
can also be malignant and invasive (i.e., spreading
to neighbouring areas).
Brain cells can be damaged
by brain tumor cells by (i) directly being compressed from
growth of the brain tumor; (ii) indirectly being affected
from inflammation ongoing in and around the brain tumor
mass, (iii) brain edema (swelling); or (iv)
increased pressure in the skull (due to brain edema
or to the blockage of the circulation of the
cerebrospinal fluid).
Local tissue
damage (either by direct or indirect mechanisms)
from brain tumors (brain cancers) causes focal neurologic symptoms, which vary due to
the location of the brain tumor. Hemiparesis,
aphasia, difficulty speaking, ataxia,
hemihypoesthesia (numbness and decreased sensation
of touch on one side of the body) and localized
headache are some of the symptoms occurring due to
the local effects of the brain tumor / brain cancer. Increased
pressure in the skull or brain edema cause more
generalized symptoms like generalized headache,
nausea and vomiting, loss of consciousness (stupor
or coma) and intellectual decline. Seizures due to
the local irritating effect of the brain tumor or
metabolic changes caused by the brain cancer are also
frequently observed. Since the development of the
skull is incomplete during infancy, infants with
brain tumor may have increased head perimeter,
bulging fontanelles or separated sutures.
Neurologic
examination reveals local (specific to the location
of the brain tumor) or generalized neurologic changes.
Slowly progressive nature of the neurologic symptoms
is suggestive of a possible brain tumor and the
diagnosis is confirmed by CT scan or magnetic
resonance imaging (MRI) of the head. Angiography,
electroencephalography (EEG) or brain biopsy may aid
in diagnosis in difficult cases. Although slow
progression is an important hallmark of the disease,
some brain tumors may enlarge very quickly and thus
may cause sudden neurologic changes.
Treatment
includes the surgical removal of the brain tumor mass or
the destruction of the brain tumor cells by radiation
(radiotherapy) and/or drugs (chemotherapy) in cases
with contraindications for a surgical operation.
Secondary
Brain Cancer
Secondary or
metastatic brain tumors / brain cancers take their origins from
tumor cells which spread to the brain from another
location in the body. They are more frequent than
primary brain tumors (primary brain cancers), and are mainly a problem in
adults, though children may also have secondary
tumors. Approximately one quarter of metastatic
cancers spread to brain.
Lung cancer and
breast
cancer
are the most common causes of secondary
brain tumors / brain cancers. Tumor cells may travel to the
brain by blood
vessels. Since the brain has no lymphatic drainage
system like other organs (cerebrospinal fluid system
acts like lymphatic system in the brain), spreading
of tumor cells by the
lymphatic route (which is very
typical for cancers of other organs) is impossible
in the brain. In contrast to primary brain tumors / brain
cancers,
metastatic tumor masses may occur in various remote
locations in the brain. Highly aggressive brain tumors / brain
cancers like glioblastomas may also be observed in
more than one location, but usually in the advanced
stages of the disease. Symptoms, diagnosis and
treatment are quite similar to those of primary
Brain tumors, however in the case of secondary tumors
the
initial location of the tumor cells must be
identified and treated as well.
Primary or
secondary brain tumors / brain cancers may cause herniation of the
brain (displacement of one part of the
brain tissue
due to mass effect of a lesion, usually causing the
compression of the neurons controlling the
respiratory system in the brainstem and eventually
death) and permanent neurologic changes including
intellectual decline.
Brain tumors
located in
distant locations may affect the nerve cells and
cause neurologic changes by mechanisms other than
direct invasion of brain tissue. Diseases caused by
the remote effects of tumor cells are called
paraneoplastic diseases. Tumors may affect brain
cells from a distance by consuming too much food and
energy that is crucial for neurons, by secreting
endocrine substances altering nerve cell functions
or – in the majority of the cases – by causing the
immune system of the body to
develop antibodies (autoantibodies)
directed against nerve cells. In the latter
mechanism,
antibodies developed to kill tumor cells
are suggested to accidentally (probably due to
molecular similarities between tumor cells and
normal nerve cells) bind neurons and destroy them.
Paraneoplastic diseases due to autoantibodies are
not confined to brain cells (e.g. Lambert-Eaton
myasthenic syndrome).
|
