Computed tomography and angiography do not reliably discriminate malignant meningiomas from benign ones.

Histological anaplasia, found in up to 10% of meningiomas, is an important prognostic sign as it is associated with increased recurrence rate and volume growth rate. We studied in retrospect a series of 230 primary intracranial meningiomas to discover whether histological anaplasia can be reliably foreseen in CT scans and angiograms. 205 meningiomas were histologically benign, and 25 meningiomas were classified as malignant (atypical or anaplastic), with either incipient (20) or overt (5) signs of anaplasia. Of ten CT parameters tested, three were associated significantly more often with malignant meningiomas: nodular contour (58.3% vs 26.7%), cysts (20.0% vs 4.4%) and absence of calcifications (92% vs 65.3%); none of these parameters was an absolute sign of anaplasia. 'Mushrooming', previously regarded as a definite sign of malignancy, was seen in 9% of benign meningiomas and in 21% of malignant ones. In angiography, no apparent differences between benign and malignant meningiomas were seen. The conclusion is that it is not possible to distinguish malignant meningiomas from benign ones with CT or angiography.