meningiomata correspond to histologic benign tumors. The metabolic phenotype of these benign recurrent meningiomata indicated an aggressive metabolism resembling that observed for atypical meningioma. Diagnosis Meningiomata are visualized readily with contrast CT, MRI with gadolinium, and arteriography, all attributed to the fact that meningiomata are extra-axial and vascularized. CSF protein levels are usually found to be elevated when lumbar puncture is used to obtain spinal fluid. On T1-weighted contrast-enhanced MRI, they may show a typical dural tail sign absent in some rare forms of meningiomas. Although the majority of meningiomata are benign, they may have malignant presentations. Classification of meningiomata are based upon the WHO classification system. Benign (Grade I) – (90%) – meningothelial, fibrous, transitional, psammomatous, angioblastic Atypical (Grade II) – (7%) – chordoid, clear cell, atypical (includes brain invasion) Anaplastic/malignant (Grade III) – (2%) – papillary, rhabdoid, anaplastic (most aggressive) In a 2008 review of the latter two categories, atypical and anaplastic-meningioma cases, the mean overall survival for atypical meningiomata was found to be 11.9 years vs. 3.3 years for anaplastic meningiomata. Mean relapse-free survival for atypical meningiomata was 11.5 years vs. 2.7 years for anaplastic meningiomata. Malignant anaplastic meningioma is aggressive. Although anaplastic meningioma has higher chances of distant metastasis than the other two types, the overall incidence of meningioma metastasis is only 0.18%; which is considered rare. Even if, by general rule, neoplasms of the nervous system (brain tumors) cannot metastasize into the body because of the blood–brain barrier, anaplastic meningioma can. Although they are inside the cerebral cavity, they are located on the bloodside of the BBB, because meningiomata tend to be connected to blood vessels. Thus, cancerized cells can escape into the bloodstream, which is why meningiomata, when they metastasize, often turn up around the lungs. Anaplastic meningioma and hemangiopericytoma are difficult to distinguish, even by pathological means, as they look similar, especially, if the first occurrence is a meningeal tumor, and both tumors occur in the same types of tissue. Although usually benign a "petro-clival" menigioma is typically fatal without treatment due to its location. Until the 1970s no treatment was available for this type of meningioma; however, since that time a range of surgical and radiological treatments have evolved. Nevertheless, the treatment of this type of meningioma remains a challenge with relatively frequent poor outcomes. Prevention The risk of meningioma can be reduced by maintaining a normal body weight, and by avoiding