allows the surgeon to plan the extent of resection around the ICA. For patients passing the TBO, an aggressive tumor resection may be pursued, and in the rare event of intraoperative ICA injury, the surgeon has the options of direct ICA repair, bypass or ICA sacrifice. If a patient does not pass the TBO, however, tumor resection around the ICA may be more conservative in order to prevent a devastating stroke. Alternatively, an arterial bypass may be performed in preparation for an aggressive tumor resection.

New modalities for imaging meningiomas are emerging. Although MRI is very sensitive and the radiological features of meningiomas have been well described, it can lack specificity and a tissue biopsy, at least, is required for definitive diagnosis. There are numerous reports of other lesions that have mimicked meningiomas on imaging, such as lymphoma, plasmacytoma, primary CNS sarcoidosis and metastases from breast, renal and prostate carcinomas. Highly specific neuroimaging is desirable to definitively diagnose meningiomas, or any other CNS lesions, non-invasively. One example of an advance in this area is MRS, which measures tissue levels of compounds such as choline, phosphocreatine/creatine and N-acetylaspar-tate. The goal of much ongoing research is to find distinct patterns of these compounds that will provide the ability to non-invasively discern the pathology and the histological grade of a neoplasm. Such information may facilitate therapeutic decisions and prognostic determinations prior to resection, or in place of biopsy.

Another type of imaging - octreotide single-photon emission computed tomography (SPECT) - has proven to be very sensitive for detecting meningiomas. Although virtually all meningiomas have octreotide-binding somato-statin receptors, it must be noted that this technique is not specific for meningiomas alone, as other primary and metastatic CNS tumors often express somatostatin receptors. The non-invasive diagnostic specificity for meningiomas is improved when octreotide-SPECT is used in combination with other neuroimaging modalities. Due to its extreme sensitivity, however, octreotide-SPECT is particularly useful for detecting the recurrence of a meningioma following resection. Some centers are even exploring the utility of combining the information from octreotide-SPECT with F-2-fluoro-2-

deoxyglucose positron emission tomograhy (FDG-PET) scanning in an attempt to predict non-invasively which tumors will behave more aggressively, but definitive results are forthcoming.

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