The term Meningioma is a name for a tumor, arising from cells that
form the covering of the brain. The covering layer is called
"meninges". The vast majority of these tumors are benign. Meningiomas
are generally well defined, discrete lesions, in sizes that vary
from a few millimeters, to many centimeters in diameter. Symptoms are
caused by compression of brain or spinal cord.
Meningiomas account for approximately 15% of all intracranial tumors.
They commonly occur in the fourth through sixth decades of life.
Meningiomas are a little more common in females and are rare in
children (only 1.5% of all Meningiomas occur in childhood). Ninety
(90%) percent of Meningiomas are intracranial while ten (10%)
percent occur within the spinal canal, most of which are in thorax
portion of the spinal column.
As with almost all other types of brain tumors, the cause of
Meningiomas is unknown. It is generally accepted that these tumors
arise from a "misguided" "CAP CELL" which is the embryonic cell of
origin that ultimately makes for the development of the "meninges"
(the covering of the brain and spinal cord.) Radiation therapy to
the brain and/or spinal cord/canal, for some other disease process,
has been implicated in subsequent Meningioma formation, especially
in children. While trauma is unusual as a cause, there are cases
of Meningiomas forming under a fracture, occurring in an area of
scarred dura, or around a foreign body. Patients with von
Recklinghausen's Disease (Neurofibromatosis), tend to develop
multiple Meningiomas at a young age. In these cases chromosomal
aberrations are regularly seen. Finally, hormonal factors may
play a role in the genesis of Meningiomas; both estrogen and
progesterone receptors have been found in Meningioma preparations.
The clinical symptoms and signs of Meningiomas are related to
those of an intracranial mass lesion, or seizure. The tumor has a
predilection for certain regions and produces symptoms and signs
specific to the tumor's location. The clinical course of a
Meningioma characteristically spans a period of years.
CT scanning (done with and without "contrast agent") can be a
definitive diagnostic method since it may show the tumor as a
homogeneously contrast-enhancing mass with well defined borders.
MRI scanning usually accurately identifies the presence of a
Meningioma when used with "contrast" enhancement (an agent known
as "Gadolinium"). MRI can superbly demonstrate the Meningioma and
its relationship to adjacent neural and vascular structures.
Finally, catheter angiography is used in some cases, when it is
necessary to demonstrate the tumor's vascularity and its blood
supply. This may be important in some cases of very vascular
tumors where pre-operative embolization, to obstruct the tumor's
blood supply, is done to facilitate surgical removal.
Meningiomas have variable neurological signs and symptoms,
depending on their location, within the nervous system.
More than 70% of Convexity Meningiomas (tumors occurring over the
top surface of the brain) are in the frontal region. If located in
this region, they may remain asymptomatic, while growing to a very
large size. Epilepsy and focal neurological signs are common.
These Meningiomas have the best potential for total removal.
These Meningiomas arise in association with the superior saggital
sinus (a major draining vein structure of the brain) and are located
in the midline. They often cause focal epilepsy, and later, paralysis,
especially of the lower extremities.
Tumors arising from the falx (the rigid midline membrane lying
between the left and right cerebral hemispheres) are located in the
midline and often extend to both sides of the brain. These tumors,
while presenting some technical challenges, are very amenable to
Olfactory Groove Meningiomas arise from the cribriform plate which
lies under the Frontal Lobe at the base of the anterior portion of
the skull. This tumor can grow bilaterally and may become large
without causing significant neurological deficits, or evidence of
increased intracranial pressure. Loss of smell can often be the only
symptom. Changes in mental status are not apparent, until the tumor
has reached a large size. Once the tumor becomes large, it impinges
on the optic nerves and chiasm, resulting in visual loss.
These Meningiomas are also at the base of the skull, lying underneath
the Frontal Lobes of the Brain, arise from the planum sphenoidale,
tuberculum sellae or the diaphragm sellae (all anatomical structures
at the base of the skull beneath the frontal lobes of the brain).
They characteristically cause early visual failure which typically
involves loss of visual acuity and progressive and asymmetric visual
field deficit. Rarely is visual loss sudden.
Meningiomas of the sphenoid ridge (a skull bone structure) are
traditionally divided into three types: outer, middle, and inner
sphenoid ridge tumors. The Outer (or Lateral) Sphenoid Ridge
Meningiomas are usually accompanied by epilepsy, focal weakness,
and trouble with language function, when present on the left side.
The tumors of the inner (or Medial) sphenoid ridge usually compress
the optic nerve and present with early unilateral visual loss. They
also may involve the cavernous sinus to cause double vision and
numbness of the face.
These constitute about 10% of all Meningiomas. The neurological
findings in these tumors can be a combination of posterior cranial
fossa and supratentorial symptoms. These can be headache, speech
disturbance, visual changes, nausea/vomiting, and balance difficulties.
These tumors can also cause extensive cranial nerve findings,
including facial weakness, hearing loss, swallowing difficulty, and
facial numbness. Depending on the specific location of the tumor
they may cause weakness and spasticity. Some of these symptoms may
mimic the usual symptoms seen with Acoustic Neuromas, Epidermoid
Tumors or Arachnoid Cysts.
The treatment options include observation, surgery and radiation.
Small tumors in older patients that do not cause symptoms can be
followed with yearly MRI scans. Since these tumors are benign and
slow growing, they may not cause any problems during the life span
of some patients.
However, in young patients, in critical locations, and when these
tumors cause symptoms (including seizures), surgical removal is the
best treatment option. Meningiomas are generally thought to be slow
growing and benign, and every effort is aimed at total removal.
Certain tumors, however, present a formidable technical challenge
because they adhere to vital neural and vascular structures at the
base of the brain. This is an area of Neurosurgical Special Interest
called SKULL BASE TUMOR SURGERY which requires a dedicated
multi-disciplinary team of specialists such as a Skull
Base/Microvascular Neurosurgeon, Craniofacial Plastic Surgery,
Neuro-otologic Surgeon, Surgical Neuro-ophthalmology among others.
In addition, MINIMALLY INVASIVE MICROENDOSCOPIC NEUROSURGICAL
TECHNIQUES may be applicable for some of these tumors.
Radiation therapy is an option for some patients with recurrent
skull base tumors, or in patients who are considered to be very poor
risks for surgery (or in the very unusual case of a tumor, in an
area where surgery is very likely to produce disastrous consequences).
Radiation is best given as stereotactic radiosurgery.
Finally, hormonal therapy with anti-estrogen agents is a possible
alternative. The long term results and effects of these agents
remain to be determined.
Meningiomas are known to recur. Many factors relate to recurrence, the
most important of which, is the extent of the original removal.
Complete resection, including removal of the dural margin, is
associated with a low rate of recurrence. Of course, Meningiomas
that are more aggressive (or the rare metastatic Meningiomas), are
associated with an increased rate of recurrence based on the
biology of their cellular components.
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This page last edited on 2/20