Diagnostic potential of magnetic resonance in cases of foramen magnum meningiomas.

Meningioma is a histologically benign tumor that is second in frequency only to gliomas among primary intracranial tumors. Its extracerebral development and generally clear demarcation from the brain does not make it easier to detect on magnetic resonance (MR) scanning. Only 2 to 3% of meningiomas occur in the foramen magnum, and these tumors are often clinically misdiagnosed. We discuss four cases of foramen magnum meningioma, with emphasis on MR scanning.