THE MRI DIAGNOSTIC SUPPORT: Magnetic resonance imaging is an efficient technique for revealing an intercranial tumor, and specifying its topography and loco-regional impact. A macroscopical approach is possible with MRI, since it distinguishes the components: tumoral tissue, cyst, necrosis and hemorrhage. DEPENDING ON THE TUMOR: Assessment of the tumoral limits is easy for extra-axial tumors. However, it is imprecise or even impossible for infiltrating intra-axial tumors. MRI specificity is low, however some lesions such as meningiomas, glioblastomas, arachnoid cysts and neurinomas are evocative.