Landau Kleffner Syndrome: Neuroradiology Aspect

Abstract

1.1 Magnetoencephalography The first recording of electromagnetic fields in the brain, or magnetoencephalography (MEG), were performed in 1968 at the Massachussets Institute of Techonology in Boston, by the David Cohen team, exploring alpha rhythm with the aid of a single sensor machine (Cohen,1968). In 1972 Cohen again studied alpha rhythm in normal subjects, and response to hyperventilation in a patient with partial complex seizures (Cohen, 1972). Until the mideighties, MEG equipment had a single sensor that in practice meant, in addition to spatial limitation of the study, that is was necessary to prolong the studies excessively until it was possible to gather the required data. Magnetoencefalography, with up to 148 channels, has been more useful in dipole localization and evaluating transcallosal spread than traditional EEG, given the limited channels in the 10-20 system. At present, over hundred MEG installations worldwide contribute to our knowledge about the function and development of the human brain (Pateau, 2002). Most MEG studies have been conducted with adult subjects, but some MEG data already exist on children. Pediatric MEG studies have mainly focused on epilepsy surgery, on the Landau-Kleffner syndrome and related disorders, on sensory cortex properties in progressive myoclonus epilepsies, and on dyslexia. MEG is a noninvasive technique that measure the magnetic fields generated by intracellular current flow in the dendrites of the pyramidal neurons of the brain cortex. The fluctuations of the magnetic field produced by this flow of current can be recorded from the outside of scalp and can subsequently be used to locate the cortical generators of that activity with a temporal resolution measured in millisecond. These characteristic made MEG an invalidly useful tool to study the brain centers of cognitive functions. The way, MEG had served to show that there is a neuronal dynamic neuronal involved in the language process (Pulvermuller,et al.,2003;Wilson,et al.,2005;Pammer,et al.,2004) and that, measuring the magnetic fields derived from that activity helps to locate the sources of electrical activity electric in the human brain in a noninvasive manner(Ray & Bowyer,2010). Despite being a relatively new technique, MEG is fast becoming an essential tool for clinical physicians, including neurophysiologist, to give an accurate diagnosis Although the main applications of the technique are found in the area of presurgical evaluation, epilepsy and