Disorders We Treat
Meningioma - Benign
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Meningiomas arise from the arachnoid "cap" cells that line the
inner "dura" (fibrous covering of the brain) and may arise anywhere
these cells are located. Most meningiomas are ovoid in shape and adhere
to the dura. Those that arise from the falx (midline septum of the brain)
or the tentorium may be dumbbell in shape.
Meningiomas can invade the bone or muscle,
but such invasion is not a sign of malignancy. Meningiomas can grow through
the holes (foramina) at the base of the skull and grow outside the skull.
As meningiomas grow, they compress the normal brain. Old hemorrhage may
be present. En plaque meningiomas are flat and hard. They grow on the
surface of the brain. Ventricular meningiomas grow in the lateral, 3rd
or 4th ventricles, and may obstruct CSF (spinal fluid) flow. Meningoimas
are rarely cystic (5% of cases). |
Epidemiology: Meningomas
account for 13% to 17% of intracranial tumors in the U.S. Multiple meningiomas
are 1% to 6% of this total. Classification of Benign Meningiomas:
Fibrous meningiomas are 7% to 25 % of of
all meningiomas. These tumors are rubbery and may contain "psammoma
bodies" when viewed under the microscope.
Transitional meningniomas are 21% to 40%
of all meningiomas. The cells are spindle shaped under the microscope.
Meningotheliomatous meningiomas, or syncytial
meningiomas are the most common and are 53% to 63% of meningiomas, depending
upon the series. The cellular nuclei are central and large. "Microcysts"
may be present.
All of these categories are histologically
and clinically "benign." Other variants, discussed elsewhere,
are not benign and include the atypical meningioma, malignant meningoma,
angioblastic meningioma.
Symptoms: Seizures occur
in approximately 50% of cases. Increased intracranial pressure (headache,
blurred vision) are common.
Treatment: The primary treatment
may include surgery. The approaches differ for the frontal, parasagittal,convexity,
sphenoid wing, olfactory groove, tentorial and cerebellopontine angle
tumors. The clival and cavernous sinus meningiomas are often treated with
radiosurgery. Unresectable meningiomas are often treated with either radiosurgery
or postoperative conventional, external beam radiotherapy.
Recurrence: Overall recurrence
rates range from 13% to 40% arnd are functions of extent of prior resection,
which in turn is a function of location (difficulty of resection).
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Meningioma - Malignant
Description: Malignant meningiomas are aggressive tumors
that arise from the meninges in the same manner as benign meningiomas.
These tumors, however, grow rapidly, invade brain (as opposed to the pushing
border of the benign meningioma) and may metastasize (spread elsewhere
in the body, usually lungs).
Classification: Classification
has not been clear in the scientific literature. Differentiation between
anaplastic meningioma and meningeal fibrosarcoma depends on the degree
of anaplasia and brain invasion. Neuropathologists have difficulty allocating
origin to fibrous cells (fibroblastic cells) vs. the meningeal cells on
occasion. This means that this tumor may be categorized as a fibrosarcoma
or a malignant meningioma. In practice, these differences are blurred.
Under the microscope, what is apparent is an aggressive appearing tumor.
Typical benign meningiomas can recur as fibrosarcomas.
Meningiomas have developed some degree
of anaplasia in approximately 12 per cent of recurrent tumors. Atypical
meningiomas are particularly likely to recur as sarcomas. If an anaplastic
tumor has areas that can be recognized as meningiomatous, it is considered
to be an anaplastic meningioma unless it is markedly anaplastic, in which
case it may be called a sarcoma. If an anaplastic meningeal tumor contains
no evidence of meningioma, it is considered to be a fibrosarcoma.
Pathology: Malignant meningiomas
are usually firm and white. Necrosis (dead tissue) can be seen microscopically.
The interface between the tumor and the normal brain is ill defined (the
tumor "infiltrates" into the brain). The surrounding edema (swelling
of the brain) can be marked. The tumor may arise in any part of the brain.
Incidence: Malignant meningiomas
occur with equal frequency in both sexes. The anaplastic forms tend to
occur in younger patients. The duration of the symptoms is shorter than
for the benign meningiomas: usually less than six months. The frequency
of seizures is higher as well (25%) and bleeding into the tumor is not
uncommon as a means of presentation. Spinal metastases can occur in 10
per cent of patients.
Treatment: The standard treatment
is surgery. The role of radiotherapy continues to be defined. There are
no randomized trials for radiotherapy vs. observation. Radiosurgery offers
intensification of dose, but the incremental gain in survival for this
modality for this tumor is not known.
The decision concerning the optimal treatment
for meningioma depends upon the complete understanding of the competing
risks vs. benefits for the different treatments. Options for meningioma
treatment may include surgery or radiosurgery. Radiosurgery is a promising
method for treatment of meningiomas as it avoids treatment of normal brain
outside the target volume and concentrates dose within the meningioma.
Two important variants of radiosurgery are important: fractionated stereotactic
radiosurgery and gamma knife.
Gamma Knife for
Meningiomas
The Gamma Knife is not a knife at all, but a radiosurgery device that
enables doctors to treat deep-seated intracranial lesions without the
risks of open-skull surgery. The "blades" of the Gamma Knife
are beams of gamma radiation programmed to bombard the lesion when they
intersect. Independently, however, these beams pass harmlessly through
the skull and surrounding tissue.Gamma Knife treatment is especially valuable
for those patients who are at high risk for surgical complications due
to other medical conditions such as diabetes or hypertension, as well
as those whose lesion is situated in an inaccessible or functionally critical
area of the brain, making a surgical approach difficult or risky.
The Gamma Knife is the most precise radiosurgical
tool; it allows neurosurgeons to direct 201 beams of radiation at the
targeted lesion. At the exact point of intersection, these beams release
potent doses of radiation. Yet, before they intersect, the individual
beams are weak and ineffectual. It is the surgical precision of the Gamma
Knife radiation that distinguishes radiosurgery from the more diffuse
radiotherapy.
The goal of radiosurgery is not to remove
the lesion but to arrest its growth. Gamma radiation works by "deranging"
molecules in tumor cells, so they stop duplicating and eventually die.
In addition to its very high success rate,
radiosurgery with the Gamma Knife has many clear advantages:
The Gamma Knife offers tremendous technical
accuracy, so a high dose of radiation can be delivered to a target with
minimum risk to nearby tissues and structures.
Since there is no incision, there are no surgical risks such as infection.
here is little patient discomfort. The patient may be lightly sedated
but is awake throughout the procedure.
Hospitalization is short—at most an overnight stay—and the recovery period
rarely lasts more than two or three days.
Because of reduced hospital stay, the cost of a Gamma Knife procedure
is often 25 to 30 percent less than traditional neurosurgery.
With unparalleled precision, the Gamma Knife delivers powerful doses of
radiation to inaccessible or inoperable lesions in the brain. Surgery
with the Gamma Knife is often referred to as "surgery without a scalpel,"
because it involves no incision, minimal pain and greatly reduced risk
for the patient.
Surgery for Meningiomas
Small, asymptomatic meningiomas can be carefully observed and followed
with serial MRI studies. Surgical resection of meningiomas always has
some risk, and the risk should be justified by the growth or size of the
meningioma or the progression of the symptoms. Complete resection of meningiomas
is often possible with tumors of the convexity, falx, lateral skull base
and the cerebellar convexity (laterally and posteriorly). These tumors
are near the surface and usually do not encase large blood vessels, involve
multiple compartments (fossae) of the skull and do not encase cranial
nerves (see skull base surgery below). Complete surgical resection of
meningiomas is usually not possible for tumors involving the superior
sagittal sinus, clivus, cerebral ventricles, tentorial notch or optic
nerve sheath. The complication rate should be less than 10 percent. Even
when removed, meningiomas are not always cured. Even after visualized
total removal of the tumor, the recurrence rate varies from 10 to 20 percent
(measured over 10 years). For patients with obvious residual tumor at
the time of resection, this recurrence rate is much higher: 30 to 50 percent.
Surgery for Skull
Base Meningiomas
For surgery of skull base meningiomas involving the cavernous sinus, medial
temporal fossa, clivus and medial petrous temporal regions, the surgery
has higher complication rates (ref) In this study a large number of preoperative,
intraoperative, and follow-up findings were analyzed for correlation with
the extent of resection. These included the presence of cranial Nerve
III, V, and VI palsies, multiple fossa involvement, and vessel encasement.
Analysis revealed that each variable tested was independently and inversely
correlated with total tumor resection (P less than 0.002). Thus for the
skull base meningiomas, alternative therapies such as radiosurgery are
often considered.
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