The radiologic modality that most likely provides the imaging information needed in a patient suspected of having a brain tumors is magnetic resonance imaging. A brain tumors can be reliably ruled out, if the standard magnetic resonance examination is performed properly and experts interpret the results as negative for tumor. In this paper we will illustrate morphological aspects of low-grade supratentorial neoplasms, including tumors of neuroepithelial tissue, such as low-grade diffuse fibrillary astrocytomas, and circumscribed astrocytic lesions (pilocytic astrocytoma, pleomorphic xantoastrocytoma and subependymal giant cell astrocytoma). Then the main practical applications of functional imaging in neurosurgery will be also debated.