Metastasis in meningioma.

Meningioma is a neoplastic growth originating from the leptomeninges. Although meningiomas are usually benign, malignant meningiomas with distant metastases occur infrequently. There is little precise information in the literature regarding the frequency of metastases in meningiomas; their incidence has been vaguely reported to be less than 1 per 1,000. Furthermore, most of the previous studies have also included haemangiopericytomas which most recent authorities do not consider meningiomas. In our experience with the management of 396 meningiomas over the past 18 years, 7 meningiomas were classified as malignant by defined histological criteria. After initially presenting as solitary intracranial neoplasms, three of the malignant meningiomas metastasized to extracranial tissues. Collectively, the metastases involved the vertebral bodies, liver, pelvis, long bones, and the spinal cord. This confers an incidence of metastasis of 0.76% when considering all the meningiomas, and an incidence of approximately 43% when considering only malignant meningioma; both percentages are significantly higher than reported previously. This high incidence of metastasis in the malignant meningioma indicates a worse prognosis than formerly assessed and also characterized the malignant meningioma as a primary central nervous system neoplasm with one of the highest rates of metastasis. In addition, when malignant meningioma is classified by following strict criteria, the risk of metastasis in the ensuing clinical course can be predicted with a higher reliability.