Imaging techniques in neoplastic meningiosis.

Since the introduction of CT and MRI as diagnostic aids, it has been possible to obtain direct images of neoplastic meningiosis. After more than ten years experience, the combination of MRI with the administration of a paramagnetic contrast medium is now accepted as the method of choice for the sensitive detection of meningeal diseases and for monitoring their treatment. The almost uniform character of leptomeningeal or pachymeningeal enhancement in the presence of infective, inflammatory, neoplastic, vascular or reactive changes is the reason for the restricted specificity of MRI, so that with the imaging process alone only very limited information about the etiology is available. Clinical data, laboratory findings, examination of the CSF and histopathological examination are therefore essential for interpreting the meningeal changes and making a differential diagnosis. Various pathophysiological processes can lead to a single meningeal enhancement visualizable with MRI: 1. a genuine disturbance of the blood-brain barrier is found in the presence of infection or inflammation, 2. leptomeningeal structures can be directly infiltrated by sheets or nodules of tumors, the blood vessels of which possess no intact blood-brain barrier, 3. physical or chemical irritants may produce of local inflammatory reaction with vascular proliferation and its corresponding enhancement, a 4. a pseudoenhancement may follow reactive dilatation of the vessels. In the present article the various appearances of neoplastic invasion of the meninges in MRI and their differential diagnosis will be described.