The Role of Diffusion Tensor Imaging and Functional Brain MRI in the Preoperative Assessment of Primary Brain Tumors

Abstract

It is all about quality of life. Quality of life is an important factor when taking the decision to undergo neurosurgery. Surgical resection is theoretically considered the ideal treatment for intracranial brain tumors. However, total resection is impossible in the vast majority of cases, due to the infiltrative nature of the tumor, and also due to the presence of eloquent cortex and important neuronal connections in the proximity of the neoplasm. Undoubtedly all brain areas are in some way of functional importance, in clinical practice the term of “functionally relevant” or “eloquent” brain region refers to those brain structures where damage can result in severe neurological symptoms and consequently in a significant reduction of the patient’s life quality. Resection of the so called “rolandic” or “central” brain tumors, for example, can cause permanent movement and sensibility impairments. It has been clearly demonstrated that intracranial glioma surgical resection reduces their mechanical mass effect on the surrounding brain, diminishes the tumor-associated edema, ensures the establishment of an accurate histological diagnosis, and induces residual tumor cells into active mitotic process, thus making them more vulnerable to any adjuvant postoperative therapy. So it became clear that the extent of resection significantly affects the survival of the patients. An aggressive surgical approach should be justified, however, only if it does not cause new permanent neurological deficits. The electric stimulation of the subcortical white matter during surgery is not very successful for reliably identifying functional white matter tracts. Also, in deep subcortical tumors, the normal position of the primary motor cortex (PMC) may be preserved, whereas only the corticospinal tract (CST) or a few fiber bundles of the CST may be displaced. In such cases, the PMC cannot be used as a landmark for the CST. Therefore, a method to noninvasively visualize the important fiber tracts and their subcomponents would be of great benefit for presurgical planning and guiding the operative procedure, as even if we avoid injury to an important cortical area, the patient could lose function if the white matter tract responsible for the function is cut. Therefore, the identification of motor, language, auditory, and visual pathways is very important for brain surgery. Diffusion tensor imaging (DTI) is a recent technique that utilizes diffusion of water molecules to make assumptions about white matter tract architecture of the brain; it is the only technique that offers the possibility for in vivo visualization of white matter tracts. The information provided by DT imaging provides precise relationships between the sub cortical white matter structures and the cerebral neoplasm. This potentially has a role in tumor characterization, and more importantly in surgical planning. Several investigators have validated DT imaging based tractography using subcortical electric stimulation because the gold standard for the identification of white matter tracts is thought to be subcortical stimulation. These studies indicated that DTI based fiber tractography offers a reliable way to map motor and language tracts throughout the brain during clinical use. Tractography based on diffusion tensor imaging (DTI) have some limitations as inability to image multiple fiber orientations within a single voxel. To address this limitation, diffusion spectrum MRI (DSI) was developed to image complex distributions of intravoxel