CT findings in malignant meningiomas.

Recurrent meningiomas are due usually to incomplete removal as in the case of basal meningiomas where the tumour surrounding vessels and nervous structures cannot be completely excised. Recurrent meningiomas of the convexity are rare after resection. In most recurrent cases histological changes are noted which may explain the rapid growth, the aggressive nature and also the malignancy of the tumour. These changes include increased mitotic activity, necrosis and invasion of the adjacent brain parenchyma. CT findings in malignant meningiomas are related to the microscopic appearance of these tumours: tumoral necrosis determines heterogeneous enhancement; brain invasion explains the irregular outline of the tumour and sometimes the absence of surrounding low attenuation area. The authors report 5 malignant meningiomas in which the CT findings are correlated with the microscopic findings.