Role of Resting State Functional MRI in epilepsy

Abstract

Epilepsy is a common and diverse set of chronic neurological disorders characterized by seizures affecting people of all ages, race and social class. There are estimated 50 million people with epilepsy in the world, of whom up to 75% live in resource-poor countries with little or no access to medical services or treatment. Epilepsy is characterized by a long term risk of recurrent seizures. These seizures may present in several ways. Nevertheless, certain epilepsy syndromes require particular precipitants or triggers for seizures to occur. Diagnostic accuracy is a particular problem in epilepsy as seizures are a symptom of diverse underlying cerebral etiologies and normally do not have any physical manifestations. Consequently a definitive diagnosis of epilepsy is often only made after an extended period of follow up and investigations. Imaging techniques have become critical in the diagnosis and management of patients with seizures and epilepsy. The impact of neuroimaging, however, extends beyond just the detection of an epileptic lesion but by contributing to the proper classification of epileptic syndromes and by delineating important aspects that separate specific epileptic disorders. Many functional imaging techniques such as SPECT, EEG and PET have played important roles in the workup and evaluation of epileptic patients prior to surgery but fMRI remains the superior principal imaging technique used in epilepsy. fMRI is simply MRI scanning in which significant tissue contrast can be attributed to blood flow and metabolism.Resting state fMRI is a powerful method of functional brain imaging that can be used to evaluate regional interactions that occur when a subject is not performing an explicit task. Major role of fMRI in epilepsy is identification of cortical regions that are organized differently in epilepsy patients either as a direct function of the disease or through indirect compensatory responses, also may help find epileptogenic tissue, whether this is a single focal location or a network of seizure-generating tissues and so it provides a more basic measure of reflecting how different brain areas are functionally connected to one another. Other useful purposes of fMRI in epilepsy include the localization of task correlated language and memory function, also it detects asymmetries in the lateralization of memory activation in patients with temporal lobe epilepsy (TLE), which is a critical aspect in both the preoperative evaluation for epilepsy surgery and for predicting postoperative memory deficits. fMRI will likely play a complementary role in patient management rather than completely replacing more invasive procedures. As with any new diagnostic modality, fMRI approaches must be carefully validated before they are incorporated into clinical decision making. 159