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Meningiomas
are usually benign tumors which arise from the meninges
covering of the brain and spinal cord, the arachnoid.
About 1 of every 5 brain tumors are meningiomas. Since
these tumors arise from the meninges, they almost always
occur over the surface of the brain or under the brain
in the skull base. These tumors generally do not invade
the brain and therefore can often be totally removed by
a craniotomy.
However even with total excision,
recurrence rates of 10% to 30% are reported, depending
upon the length of follow-up. Skull base meningiomas
often are more challenging to remove. Multiple
meningiomas occur in 5% of patients, and meningiomas
constitute 25% of intraspinal tumors. Rarely meningiomas
may be malignant with rapid growth, invasion of the
brain and frequent recurrence after surgery or
radiation.
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| Meningiomas
become symptomatic in several ways. During their slow
growth they may irritate the brain causing epileptic
seizures. Alternately, these tumors may compress
adjacent brain producing progressive neurological
symptoms, such as progressive weakness, or visual loss.
Often these symptoms can be very subtle: progressive
dementia or apathy may mimic depression in some patients
with frontal meningiomas. Tumor which begin near less
critical brain regions (so-called "silent
brain") may become quite large producing symptoms
of increased intracranial pressure such as headache and
visual loss. On rare occasions these tumor may
spontaneously bleed, producing an abrupt neurological
deficit: a stroke. Spinal meningiomas produce
progressive weakness and numbness...interestingly these
spinal tumors are much most frequently seen in elderly
females. |
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| Fortunately
meningiomas are relatively easy to diagnose as they have
characteristic appearances on CT or MR images. Sometimes
cerebral angiograms and MR spectroscopy can clinch the
diagnosis in difficult cases.
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A
54 year old presented with speech difficulty as was
found to have a very large left frontal convexity meningioma
compressing the brain. Total tumor removal of this
convexity meningioma by craniotomy
with image guidance.
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| The
treatment of meningiomas include watchful waiting, open
surgery, radiosurgery and radiation therapy Chemotherapy
and hormonal manipulation have minor roles in the
management of these tumors.
A
number of meningimas, especially those tumors found to
be calcified on CT or MR imaging do not grow. Hence one
option for those harboring a small and asymptomatic
tumor is to obtain serial scans over months to years to
avoid further treatment.
Open
surgery has been the gold standard of meningioma
therapy. The aim of surgery is to completely remove the
tumor. Tumors which arise over the convexity of
the head are the easiest to operate and cure. Those
tumors at the skull base present a greater risk of
surgery and greater recurrence rates. Other factors
which influence surgical cure rates include the size of
the tumor and involvement of critical brain structures
which may lead to subtotal removal and the finding of
malignancy. Malignant meningiomas can spread to other
regions of the body, especially the lungs and regional
lymph nodes. Navigation with optical tracking systems
greatly aids surgery. as does the use of the operative
microscope and ultrasonic aspiration. Endovascular
embolization of these tumors may reduce blood loss
during surgery.
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A
right parietal convexity meningioma
causing seizures. Note the surface
vein adjacent to the tumor..........
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The
tumor has been removed and
the surface veins preserved....... |
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| Gamma
Knife radiosurgery is becoming an important means of
treating these tumors, either as primary treatment to
avoid the risk of surgery, or to treat recurrent or
residual tumors following surgery. A 95% control rate is
expected after Gamma Knife radiosurgery. Radiosurgery
avoids surgical complications of pain, bleeding,
infection and neurological deficits. The technique can
be performed in a few hours, on an outpatient basis,
allowing individuals to return to work in a matter of
days. Because the radiation is confined to the
tumor, the surrounding, normal brain receives little
radiation. The procedure is safe. We have treated more than
250 meningiomas at the San Diego Gamma Knife Center,
often as the primary treatment. |
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| Radiation
therapy can control the growth of meningiomas. Probably
80 to 90% of tumors undergoing fractionated radiation
therapy to a total dose of 54 Gy do not re-grow. XRT has
the disadvantage that a considerable volume of normal
brain tissue may be radiated with long range deleterious
effects. |
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Some
meningiomas contain estrogen and progesterone receptors.
However there appears to be little value in treating
these tumors with tamoxifen, an estrogen antagonist.
Selected patients have responded to RU 38486. Few tumors
respond to hydroxyurea and chemotherapeutic agents in
common use for various malignant tumors.
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