FORAMEN MAGNUM MENINGIOMA: THE INTEREST OF THE COUPLE CT-

MRI IN THE PRECISE ASSESSMENT OF THE LESION.

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

INTRODUCTION 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

CLINICAL CASE

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

IMAGING DATA 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

IMAGING DATA

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

DISCUSSION

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).

DISCUSSIONDefinition

DISCUSSION 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.

Clinical diagnosis

DISCUSSION

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

DISCUSSION

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.

Classification

DISCUSSION

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

DISCUSSION

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

DISCUSSION 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

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

Neuroimaging

DISCUSSION

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

Diagnosis differential

CONCLUSION 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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