Radiology Resident Case of the Week
Bao Nguyen, M.D.
Peer Review Status: Internally Reviewed by Daniel
Crosby, M.D.
Imaging:
The spin-echo images demonstrate a large ovoid mass along the lateral aspect of the left sphenoid wing, which is associated with a surrounding amorphous cystic structure. There is considerable mass effect and edema in the adjacent white matter of the left frontal and left parietal lobes (best appreciated on the T2 weighted images), causing midline shift of the septum pellucidum and dilatation of the lateral ventricles. Transependymal flow (best appreciated on the proton density images) is also seen and consistent with obstruction of the cerebral aqueduct from compression of the midbrain by uncal herniation.
With gadolinium DTPA, there is intense uniform enhancement of the solid portion of this lesion, which is associated with a long dural tail.
The cerebral arteriograms show a large tumor blush in the left temporal lobe with parasitized blood flow from branches of both the internal and external carotid arteries. Note the classic angiographic "Mother-in-law" sign, i.e. tumor blush that arrives early and stays late, and the enlarged middle meningeal artery.
Diagnosis:
Large sphenoid wing meningioma with associated cyst causing
significant mass effect with resultant uncal herniation, compression
of the 3rd ventricle and a trapped right lateral ventricle.
Etiology/Epidemiology/Pathology:
Meningiomas are the prototypical extra-axial intracranial neoplasm
and the most common nonglial CNS tumor, accounting for 15-20% of all
primary intracranial neoplasm. Meningiomas are thought to arise from
meningo-endothelial cells lining the arachnoid granulations, but
specific tissue types vary and histologic classification schemes have
been devised to categorize lesions into syncytial, transitional,
fibroblastic, angioblastic and malignant types.
The majority of meningiomas are asymptomatic and solitary, but up to 10% are multiple and associated with Neurofibromatosis type II. Most meningiomas are found incidentally on imaging studies or at autopsy, but when symptoms occur they may include seizures, hemiparesis, visual field defects and cranial nerve palsies, depending on their location. The vast majority of meningiomas are supratentorial, frequenting the parasagittal dural convexities (50%), sphenoid wing (20%), cerebellopontine angles (10%), olfactory groove and planum sphenoidale (10%). The petrous temporal bone and clivus are common infratentorial locations. Intraventricular meningiomas are rare but typically occur around the choroid plexus in the trigone of the lateral ventricles. Most intraventricular meningiomas calcify.
Meningiomas may be associated with cystic encephalomalacia caused by the formation of degenerative brain parenchyma or trapped arachnoid mater with resultant pooling of CSF. Vasogenic edema from compressive ischemia, venous stasis or parasitization of pial vessels may also occur and can be extensive.
Although the diagnosis of a meningioma can be readily made by MRI, pre-operative angiography may still play an important role in assessing the size and location of feeding arteries, the venous drainage pattern, and the vascularity of the tumor, as well as the relatiohship between the tumor and important adjacent structures. Additionally, angiography may be used therapeutically to provide preoperative tumor embolization.
Miscellaneous:
Meningiomas occur more commonly in women and may increase in size
during pregnancy.
DDX:
The differential diagnosis of any brain lesion is best generated
after one answers the fundamental question of whether or not the
lesion is intra or extra-axial. Radiographic findings which suggest
an extra-axial location include: 1) displacement of cortical vessels;
2) trapping of CSF between the mass and brain parenchyma; 3) buckling
of subjacent cortex; and 4) lack of surrounding infiltration . Once
the location is established, the differential list for an extra-axial
lesion is limited to two common disease entities: a meningioma or
schwannoma.
Key Referrences:
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