Download Tentorial Meningiomas

Tentorial Meningiomas
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Meningiomas of the posterior cranial fossa account for
~9% of all intracranial meningiomas.
Approximately 3 to 6% of all intracranial meningiomas
and ~30% of posterior fossa meningiomas originate from
the tentorium cerebelli.
Classification
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1)Meningiomas arising from the free tentorial notch(T1-T2)
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anterior
middle
posterior
2)Meningiomas originating from the intermediate
tentorial surface(T4)
3)Meningiomas involving the torcular Herophili(T5)
4)Meningiomas arising from the lateral outer tentorial
ring(T6-T7)
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posterior
anterior
5) falcotentorial meningiomas(T3-T8)
Superior
Petrosal
Sinus
1
5
Transverse
Sinus
2
3
4
Straight
Sinus
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The straight sinus receives the vein of Galen and the
inferior sagittal sinus at the tentorial apex and runs
posteriorly to meet the transverse sinuses from both
sides and the superior sagittal sinus from above at the
torcular Herophili.
The tentorial incisura is divided into an anterior incisural
space located in front of the brain stem, a middle incisural
space situated lateral to the brain stem, and a posterior
incisural space located behind the brain stem
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At the anterior incisural space, the most important
neurovascular structures in close proximity include the
oculomotor nerve, the basal vein, the posterior
communicating artery, the anterior choroidal artery, the
P1 and proximal P2 segments of the posterior cerebral
artery, and the superior cerebellar artery. Less often, the
optic nerve and the optic chiasm may be involved.
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The trochlear nerve, the anterior choroidal artery, the P2
segment of the posterior cerebral artery, the superior
cerebellar artery, and the basilar vein constitute the
neurovascular contents of the middle incisural space.
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The ambient cistern continues posteriorly into the
quadrigeminal cistern, which is the main cistern of the
posterior incisural space. This space forms the pineal
region and is related to anterior falcotentorial
meningiomas.
It contains the trunks and branches of the posterior
cerebral and superior cerebellar arteries, and the vein of
Galen, which receives the paired internal cerebral and
basal veins. The trochlear nerve exits from below the
inferior colliculi, curves around the dorsal midbrain, and
enters the ambient cistern in the middle incisural space
Clinical Presentation
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Patients harboring a infratentorial meningioma, the
most often encountered subtype, commonly present with
headache, dizziness and gait unsteadiness.
Clinical examination usually reveals a gait ataxia and
occasionally impairment of the vestibulocochlear nerve.
Hearing loss may be caused by direct involvement of the
eighth cranial nerve (CN), or it may be the result of
distortion of the central auditory pathways, such as the
lateral lemniscus or the inferior colliculi.
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Supratentorial meningiomas, particularly those
closely related to the medial temporal lobe, may present
with seizures.
T1–T2 meningiomas may intimately involve the brain
stem and the fifth CN. Accordingly, patients may present
with hemiparesis, trigeminal neuralgia, and facial numbness
Patients with T3–T8 meningiomas often present with
headache.
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Mental changes are reported in up to 46% of patients and
a gait ataxia in 43 to 62% of cases. A homonymous
hemianopsia is present in 20 to 46% of these patients.
Diagnostic Workup and
Preoperative Considerations
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Triplanar contrast-enhanced T1-weighted MRI
gives the most accurate information for planning the
surgical approach. The dural attachment zone and extent
of the tumor, displacement of the brain stem,
displacement or engulfment of vertebrobasilar arteries,
invasion of the cavernous sinus, and patency of the
straight, transverse, and sigmoid sinuses can be sufficiently
studied.
A nonvisible venous sinus on MRV(magnetic resonance
venography) or catheter angiography may prove to be
patent during surgery.
Surgical Approach
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The lateral suboccipital retrosigmoid approach is
suitable for most infratentorial T1–T2 and T6–T7 tumors
The supracerebellar infratentorial route may be
more appropriate in more medial infratentorial T1–T2
tumors and in infratentorial T3–T8 tumors, and it is the
approach of choice in infratentorial T4 tumors
The usual avenue for resection of T3–T8 meningiomas is
the occipital transtentorial approach
Supratentorial T1–T2 and T6–T7 tumors can usually be
resected via a subtemporal route.
Clinical case 1
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Preoperative T1-weighted contrast-enhanced magnetic
resonance imaging (MRI) in the axial and coronal plane
demonstrates an infratentorial T6–T7 meningioma in a
patient with gait unsteadiness and rightsided impairment
of hearing. Note patency of the transverse sinus (white
arrow)
Before
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Intraoperative photograph after resection of the tumor
via a retromastoid craniotomy.
Note the trochlear nerve (white arrow) as viewed through
the tentorial incisura. Also shown are the cerebellum
(black asterisk), hyperemic tentorium after tumor resection
(white asterisk), and surgical cotton (black plus sign).
After
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Postoperative T1-weighted contrast-enhanced MRI shows
unintended occlusion of the transverse sinus in the axial
view (white arrow) and contrast enhancement of the
hyperemic tentorium.
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In the coronal view (white arrow). Occlusion of the venous
sinus was without sequelae, and preoperative symptoms
and signs, including hearing impairment, resolved
Clinical case 2
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T3–T8 meningioma displayed in preoperative sagittal
contrast-enhanced T1-weighted magnetic resonance
imaging (MRI) in a patient presenting with gait ataxia and
slight mental deficits. Note the patency of the straight
sinus and accompanying obstructive hydrocephalus due to
occlusion of the aqueduct
Before
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An intraoperative photograph shows the tumor as viewed
via the supracerebellar infratentorial approach.
After
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A second intraoperative photograph reveals the pineal
region above the cerebellum (black arrows) and below the
tentorium (black asterisk) after resection of the meningioma.
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Three months postoperative sagittal contrast-enhanced
T1-weighted MRI demonstrates removal of tumor. Note
patency of the aqueduct, straight sinus, inferior sagittal
sinus, vein of Galen, and internal cerebral veins.
Obstructive hydrocephalus and preoperative neurological
symptoms resolved.
Literature:
Thieme-Al-Mefty’s Meningiomas- page(168-176)