IMAGING TECHNIQUES IN NEOPLASTIC MENINGIOSIS

Since the introduction of CT and MRI as diagnostic aids, it has been p ossible to obtain direct images of neoplastic meningiosis. After more than ten years experience, the combination of MRI with the administrat ion of a paramagnetic contrast medium is now accepted as the method of choice for the sensitive detection of meningeal diseases and for moni toring their treatment. The almost uniform character of leptomeningeal or pachymeningeal enhancement in the presence of infective, inflammat ory, neoplastic, vascular or reactive changes is the reason for the re stricted specificity of MRI, so that with the imaging process alone on ly very limited information about the etiology is available. Clinical data, laboratory findings, examination of the CSF and histopathologica l examination are therefore essential for interpreting the meningeal c hanges and making a differential diagnosis. Various pathophysiological processes can lead to a single meningeal enhancement visualizable wit h MRI: 1. a genuine disturbance of the blood-brain barrier is found in the presence of infection or inflammation, 2. leptomeningeal structur es can be directly infiltrated by sheets or nodules of tumors, the blo od 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 pseu doenhancement may follow reactive dilatation of the vessels. In the pr esent article the various appearances of neoplastic invasion of the me ninges in MRI and their differential diagnosis will be described.