Abstracts

Rationale: Rationale: The ictus is a dynamic process that typically affects multiple cortical areas. Analysis of propagation patterns is important to define the epileptic network. The pattern of propagation is not well defined by static methods. Voltage maps depicts the distribution of the electrical fields associated with the epileptic activity at a given time. We present the use of combined MRI imaging, intracranial electrode recording and source localization/coregistration to visualize epileptic propagation patterns in a dynamic manner in a patient with intractable epilepsy.Methods: Methods: Subdural electrodes were implanted in a patient with left temporal lobe epilepsy who had normal MRI and left language and memory dominance. Electrode placement was confirmed with a head CT, and electrographic seizures were recorded. The CT images were coregistered with patient head MRI and electrocortical data. Source modeling using commercially available software (Curry 7, Compumedics) rendered electrical field potential changes in real time. Registration of the propagation patterns of interictal spike, subclinical electrographic seizures and a electroclinical seizure where recorded and converted to a video clip.Results: The dynamic observation of the voltage map propagation patterns were different between the interictal spike, the subclinical seizure and the electroclinical seizure. The spike started in the temporal pole and propagated to the anterior medial structures followed by a repolarization wave at the onset (figure 1). The subclinical seizure had two different propagation patterns, the first pattern originated in the lateral anterior temporal area and propagated to the posterior lateral cortex and inferior temporal cortex. The second pattern occurred later within the same ictal event and propagated both anterior lateral and posterior lateral cortex (figure 1). The electroclinical seizure had a circular propagation loop starting in the anterior temporal pole (same as the onset of the spike) and propagated clockwise involving the superior temporal cortex, spreading to lateral cortex followed by posterior lateral cortex at the same time of a repolarization wave at the onset. The circuit start over again at the anterior temporal pole and continues with the same pattern (figure 2). The video clip with results will be shown. Conclusions: Conclusion: Combined imaging and source localization, analyzed to provide dynamic visualization of seizure propagation patterns is practical and useful to gain insight of the dynamics associated with the transition from interictal to ictal activity. Both interictal and ictal discharges were originated in the same region but only the oscillations associated with a clinical seizure were characterized by a recurrent cyclical spatial loop within the temporal lobe. The cyclical propagation pattern correlates with rhythmic ictal activity and may characterize the difference between interictal and ictal discharges.