Imaging of central nervous system tumors.

Magnetic resonance imaging has been used increasingly in the staging and evaluation of neoplasia of the brain and leptomeninges. In the classification of gliomas, the MR accuracy rate approaches that of pathologic diagnosis. Contrast-enhanced MR imaging has improved specificity in evaluating brain tumors in children and is now the preferred modality for evaluating leptomeningeal metastases of the brain and spine. MR imaging in children has also increased the specificity of histologic diagnosis in hypothalamic hamartoma and juvenile pilocytic astrocytoma. Gadolinium enhancement is most useful in patients older than 35 years of age who have focal neurologic complaints and certain disease histories. The expense of gadolinium contrast material is the major drawback to its routine use. In patients with seizure disorder, MR imaging is more sensitive than CT for detecting abnormalities such as mesial temporal sclerosis, tumors, and vascular malformations. Gadolinium enhancement may be useful in differentiating tumors from mesial temporal sclerosis. Recent reports on the use of MR spectroscopy for evaluating brain metabolism and tumors demonstrate that differences in metabolites exist. A correlation was found in epidermoid tumors between high signal on T1-weighted images and high lipid content, and several studies have shown a positive correlation between glioma grade and glycolytic activity as determined on 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography.