What is a Brain Tumor?
brain tumor is any intracranial mass created by an abnormal and
uncontrolled growth of cells either normally found in the brain
itself: neurons, glial cells (astrocytes, oligodendrocytes,
ependymal cells), lymphatic tissue, blood vessels), in the cranial
nerves (myelin producing Schwann cells), in the brain envelopes (meninges),
skull, pituitary and pineal gland, or spread from cancers primarily
located in other organs (metastatic tumors).
Primary (true) brain tumors are commonly located in the posterior
cranial fossa in children and in the anterior two-thirds of the
cerebral hemispheres in adults, although they can affect any part of
In the United States in the year 2000, it was estimated that there
were 16,500 new cases of brain tumors1, which accounted for 1.4% of
all cancers, 2.4% of all cancer deaths2, and 20%?25% of pediatric
cancers2,3. Ultimately, it is estimated that there are 13,000
deaths/year as a result of brain tumors.
Aside from exposure to vinyl chloride
or ionizing radiation, there are no known environmental factors
associated with brain tumors. Mutations and deletions of so-called
tumor supressor genes are incriminated in some forms of brain
tumors. Patients with various inherited diseases, such as Von
Hippel-Lindau syndrome, multiple endocrine neoplasia,
neurofibromatosis type 2 are at high risk of developing brain
The kind of symptoms brain tumors may
cause depend on two factors: tumor size (volume) and tumor location.
The time point of symptom onset in the course of disease correlates
in many cases with the nature of the tumor (enign, i.e.
slow-growing/late symptom onset, or malignant, i.e. fast
growing/early symptom onset).
Many low-grade (benign) tumors can remain asymptomatic
(symptom-free) for years and they may accidentally be discovered by
imaging exams for unrelated reasons (such as a minor trauma)
New onset of epilepsy4 is a frequent reason for seeking medical
attention in brain tumor cases.
Large tumors or tumors with extensive perifocal swelling edema
inevitably lead to elevated intracranial pressure (intracranial
hypertension), which translates clinically into headaches, vomiting
(sometimes without nausea), altered state of consciousness
(somnolence, coma), dilatation of the pupil on the side of the
lesion (anisocoria), papilledema (prominent optic disc at the
funduscopic examination). However, even small tumors obstructing the
passage of cerebrospinal fluid (CSF) may cause early signs of
intracranial hypertension. Intracranial hypertension may result in
herniation (i.e. displacement) of certain parts of the brain, such
as the cerebellar tonsils or the temporal uncus, resulting in lethal
brainstem compression. In young children, elevated intracranial
pressure may cause an increase in the diameter of the skull and
bulging of the fontanelles.
Depending on the tumor location and the damage it may have caused to
surrounding brain structures, either through compression or
infiltration, any type of focal neurologic symptoms may occur, such
as cognitive and behavioral impairment, personality changes,
hemiparesis, (hemi)hypesthesia, aphasia, ataxia, visual field
impairment, facial paralysis, double vision, tremor etc. It cannot
be stressed enough that these symptoms are not specific for brain
tumors - they may be caused by a large variety of neurologic
conditions (e.g. stroke, traumatic brain injury). What counts,
however, is the location of the lesion and the functional systems
(e.g. motor, sensory, visual, etc.) it affects.
A bilateral temporal visual field defect (bitemporal hemianopia?due
to compression of the optic chiasm), often associated with endocrine
disfunction?either hypopituitarism or hyperproduction of pituitary
hormones and hyperprolactinemia is suggestive of a pituitary tumor.
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