Abstracts

Rationale: Simultaneous scalp EEG-functional MRI (EEG-fMRI) is a well-established technique for the imaging of the Blood Oxygen Level Dependent (BOLD) response associated with interictal epileptiform discharges (IED) in patients with epilepsy. Unlike scalp EEG, intracranial EEG (iEEG) can accurately record activity that is of too low amplitude or deep in origin to be seen by scalp EEG. By combining intracranial EEG with simultaneous fMRI (iEEG-fMRI), we are able to image patients with very discrete or deeply located epileptogenic tissue, such as the mesial temporal structures (e.g., hippocampus or amygdala). We have previously confirmed the low risk associated with using intracranial electrodes in a high-field (3T) MR environment. This project was designed to assess the BOLD response to focal iEEG discharges originating from mesial temporal sources in patients with MR-negative, independent bi-mesial temporal epileptiform discharges using simultaneous iEEG-fMRI at 3 T. Methods: Two MR negative patients with suspected independent bi-mesial temporal lobe epilepsy undergoing intracranial video-EEG monitoring for seizure focus localization were recruited and underwent iEEG-fMRI. Subjects were connected to a MR compatible EEG system (Neuroscan, Charlotte, NC) and simultaneous iEEG-fMRI was performed at 3 T using a GE scanner (GE, Waukesha, WI). Epileptiform discharges were identified and marked by two experienced electroencephalographers (PF, YA). The timing of epileptiform events was used to generate parametric maps of significant BOLD activation. Results: 2092 IEDs were recorded from a left mesial temporal electrode in Subject 1 and 2035 discharges from a right mesial temporal electrode in Subject 2, generating parametric maps characteristic of the BOLD signal changes associated with these events (Figure 1). The areas of activation in both patients appear strikingly similar: a significant BOLD cluster appears unilaterally in the left (subject 1) or right (subject 2) mesial temporal lobe. Additionally, bilateral insular activation was seen in both patients, as well as bilateral occipital and bilateral postcentral gyrus (somatosensory cortex) activation. Conclusions: Based on these preliminary data, patients with MR negative, independent, bi-mesial temporal lobe epileptiform discharges may possess widespread epileptic networks associated with their IEDs. These findings may help elucidate the underlying systems associated with this semiology and guide clinical decision-making in these difficult to treat patients.