Transcript FORAMEN MAGNUM MENINGIOMA: THE INTEREST OF THE

S.BELABBES, N.ELYOUSFI, S.CHAOUIR, T.AMIL, A.HANINE , H.EN-NOUALI
Department of Radiology, Military Teaching
Hospital Mohammed V of Rabat. Morocco
NR31
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rare, representing 1,8 to 3, 2% of intracranial
meningiomas.
Among the meningiomas of the posterior fossa,
foramen magnum (FM) meningiomas deserve special
consideration because of their characteristics in
symptomatology, and complications
They are causing a high risk of spinal cord
compression.
Several classifications, with a surgical interest, have
tried to categorize them according to dural attachment,
which underscores the value of MRI
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A 33-year-old female presented with mild headache
lasting for a year, neurological examination revealed
paresthesia in upper limbs. A CT brain scan and an
MRI were performed
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CT showed a process in the level of the foramen
magnum spontaneously isodense that enhances after
injection of contrast.
CEREBRAL CT C+: large tumor occupies
slightly more than half of the transverse
diameter of the foramen magnum. the rostral
spinal cord is compressed
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MRI objectified a process with broad-base dural
implantation at the expense of the clivus, in isosignal
T1 and hypersignal T2, enhanced after injection of
contrast. This process drove back the spinal cord
behind, coming in contact with the vertebral artery
which is not narrowed. The patient was operated and
anatomopathological examination found a
meningioma of the foramen magnum
MRI SAGITAL SECTION
MRI T1:a large anterior foramen
magnum meningioma isointense to
surrounding brain severely
compresses the neuraxis
MRI T2: pocess hyperintense to
surrounding brain
homogeneously enhancing tumor arises
predominantly in an anterior location
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Meningiomas are common neoplasms representing
14.3 to 19% of all intracranial tumors.
Slowgrowing benign tumors arising at any location
where arachnoid cells reside.
Among all the meningiomas, only 1.8 to 3.2% arises at
the foramen magnum (FM).
Definition
Clinical diagnosis
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The indolent development at the craniospinal junction
makes clinical diagnosis complex and often leads to a
long interval between onset of symptoms and
diagnosis.
Clinical presentation of the FM lesions may be in form
of neck pain, dysasthesiasis in the upper limbs,
quadriparesis or quadriplegia, cruciate hemiparesis,
impaired pain and touch sensations and occasionally
pseudoathetoid movements of the hands.
Classic foramen magnum syndrome is defined by
development of unilateral arm sensory and motor
deficits, which progress to the ipsilateral leg, then the
contralateral leg, and finally contralateral upper
extremity.
Classification
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FM meningiomas arise from arachnoid at the
craniospinal junction.
The borders of this zone, range anteriorly from the
lower third of the clivus, to upper margin of the body
of C-2, laterally from the jugular tubercle to the upper
margin of the C-2 laminae, and posteriorly from the
anterior edge of the squamous occipital bone to the C-2
spinous process.
Classification
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the classification of these lesions is based on their size
relative to that of the foramen magnum:
 small, lower than one third the transverse dimension
of the foramen magnum
 medium, one third to one half its dimension
 large, superior with one half
Most lesions arise anterolaterally
Posterolateral origin is the second most frequent,
Purely posterior lesions the third
The least common are entirely anterior.
Neuroimaging
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Neuroimaging confirms the clinical diagnosis and
allows the planning of a surgical approach.
The diagnosis of FMM is essentially based on
morphological criteria.
 It is extra-axial with a large insertion base and obtuse
angle connection.
 wider than thick.
 The reaction in the vicinity of bone insertion area is less
than Supratentorial findings , but has a high diagnostic
value when it exists in the form of bone erosion or
hyperostosis
Neuroimaging
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the decreasing Thickening of the dura and the
contrast enhancement "comet tail" adjacent to the
meningioma is highly suggestive of meningioma,
but not specific, it is met in 59% to 71% of cases.
Magnetic resonance imaging:
 Modality of choice for defining tumors of the
foramen magnum.
 provides high-resolution images of soft-tissue
anatomy that is not susceptible to degradation by the
surrounding skull base, a pitfall of CT scanning.
 On T1-weighted image: meningiomas may appear
isointense, mildly hypointense, or hyperintense to
surrounding brain.
Neuroimaging
On T2-weighted image: isointense to slightly
hyperintense compared with brain
 The T1-weighted enhanced contrast imaging shows the
dural attachment site of the tumor and it provides ready
discrimination between tumor and brainstem
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Once the diagnosis of meningioma evoked, MRI
should focus on:
locate the tumor in the axial plane at the foramen
magnum: anterior, lateral or posterior
 define the compartment where it develops: intra dural or
extradural or both (in most cases is intradural)
 clarify its relation to the adjacent vertebral artery which
can be invaded by the meningioma
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Diagnosis differential
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Other tumors such as neuromas and metastasis
vascular lesions such as vertebro basilar aneurysm
benign tumors of the clivus especially meningiomas,
and tumors of the jugular foramen extending to the
foramen magnum
Retro clival meningioma that is not always easy to
differentiate of the foramen magnum meningioma
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the Foramen magnum meningioma is an uncommon
intracranial tumor that presents a particular gravity
because of the risk of bulbo-medullary compression.
CT and MRI comprise the essential of current
meningioma imaging, and the diagnostic information
provided by these modalities is complementary.
MRI provides excellent soft tissue resolution, while CT
far superiorly demonstrates the bone changes.
The relationship of the FMM with vertebral artery and
the lower cranial nerves is important, and must be
mentioned.
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