Late malignant transformation of anaplastic meningioma 18 years after primary surgery: A case report.

Meningiomas rarely progress to malignant variants and there is no consensus regarding the period over which malignant transformation may occur. Here, we report a case of anaplastic meningioma that showed malignant transformation 18 years after gross total resection of benign meningioma in the primary surgery, which may be the longest duration reported to date. Although the recurrence rate is low following total resection of benign meningioma, malignant transformation can rarely occur after a long period as in our case. Long-term follow-up after total resection of benign meningioma is suggested considering the risk of malignant transformation.