Patients with meningiomas are often referred to the neurosurgeon after a primary care physician or neurologist has obtained a CT scan of the head for a variety of neurological symptoms. The radiological appearance of meningiomas with this modality of imaging has been well described. Meningiomas are typically isodense on CT before contrast and homogeneously hyperdense following intravenous iodinated contrast. In addition to being inexpensive and convenient, CT offers the advantages of determining the extent of hyperostosis and the degree of tumor calcification, both of which add to the diagnostic accuracy and help the surgeon with surgical planning.
It is, however, becoming more frequent that the initial head scan performed is magnetic resonance imaging (MRI), due to its increasing availability and decreasing cost. MRI is proven to be the gold standard neuroimaging method of detection for meningiomas. MRI with and without gadolinium contrast is necessary to precisely delineate the full extent of the tumor, particularly in the case of skull base tumors that can involve critical neurovascular structures (such as the optic nerve(s) and major intracranial vessels). On Tl-weighted MRI, the majority of meningiomas are isointense, while the remainder is slightly hyperintense to grey matter. Contrast-enhanced Tl-weighted images reveal dramatic and usually homogeneous enhancement of meningiomas and, often, their associated "dural-tail". On T2-weighted sequences, nearly 50% of all meningiomas are hyperin-tense, while the other half are isointense to grey matter. T2-weighted sequence is also highly sensitive in delineating the extent of peritumoral edema. Furthermore, utilization of MRI allows the opportunity to obtain MR-angiography (MRA) and/or MR-venography (MRV) in order to better visualize the extent of vascular involvement, particularly the patency of dural sinuses and the encasement of major arteries. Moreover, the contrast-enhanced MRI is essential in detecting any residual or recurrent tumor following surgery.
For large meningiomas, cerebral angiography may be helpful to determine precisely the extent of involvement of the intracranial arteries and their branches, in addition to providing further information regarding the venous anatomy. Also, large tumors may have significant arterial supply from the external carotid and middle meningeal arteries that may be safely embolized during the angiogram. Many posterior fossa meningiomas are fed by vessels not amenable to catheterization or successful embolization. However, in rare instances of successful embolization of deep-seated, large posterior fossa meningiomas, surgery is dramatically facilitated by embolization. Therefore, in the authors' practice, all supratentorial meningiomas larger than 4-5 cm and infratentorial meningiomas larger than 3-4 cm are routinely evaluated for possible embolization.
When the internal carotid artery (ICA) is noted to be completely encased and/or narrowed by the tumor on pre-operative MRI, ipsi-lateral ICA test balloon occlusion (TBO) may be performed. Such information is helpful as it
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