Clinical benefit of presurgical EEG‐fMRI in difficult‐to‐localize focal epilepsy: A single‐institution retrospective review

Abstract

Objective: The aim of this report is to present our clinical experience of electroencephalography-functional magnetic resonance imaging (EEG-fMRI) in localizing the epileptogenic focus, and to evaluate the clinical impact and challenges associated with the use of EEG-fMRI in pharmacoresistant focal epilepsy. Methods: We identified EEG-fMRI studies (n = 118) in people with focal epilepsy performed at our center from 2003 to 2018. Participants were referred from our Comprehensive Epilepsy Program in an exploratory research effort to address often difficult clinical questions, due to complex and difficult-to-localize epilepsy. We assessed the success of each study, the clinical utility of the result, and when surgery was performed, the postoperative outcome. Results: Overall, 50% of EEG-fMRI studies were successful, meaning that data were of good quality and interictal epileptiform discharges were recorded. With an altered recruitment strategy since 2012 with increased inclusion of patients who were inpatients for video-EEG monitoring, we found that this patients in this selected group were more likely to have epileptic discharges detected during EEG-fMRI (96% of inpatients vs 29% of outpatients, P<.0001). To date, 48% (57 of 118) of patients have undergone epilepsy surgery. In 10 cases (17% of the 59 successful studies) the EEG-fMRI result had a "critical impact" on the surgical decision. These patients were difficult to localize because of subtle abnormalities, apparently normal MRI, or extensive structural abnormalities. All 10 had a good seizure outcome at 1 year after surgery (mean follow-up 6.5 years). Significance: EEG-fMRI results can assist identification of the epileptogenic focus in otherwise difficult-to-localize cases of pharmacoresistant focal epilepsy. Surgery determined largely by localization from the EEG-fMRI result can lead to good seizure outcomes. A limitation of this study is its retrospective design with nonconsecutive recruitment. Prospective clinical trials with well-defined inclusion criteria are needed to determine the overall benefit of EEG-fMRI for preoperative localization and postoperative outcome in focal epilepsy. K E Y W O R D SEEG, epilepsy surgery, fMRI, focal epilepsy 50 | KOWALCZYK et AL. SUPPORTING INFORMATIONAdditional supporting information may be found online in the Supporting Information section.

Temporal Lobe Spikes Affect Distant Intrinsic Connectivity Networks

“…In agreement with a recent retrospective review investigating the clinical impact of EEG-fMRI in the presurgical setting (31), our results suggest that in patients with TLE short EEG-fMRI recordings are not useful for the surgical decision. When a clear epileptogenic lesion is detected on structural MRI, which matches the epileptogenic focus defined by the video-EEG data, EEG-fMRI might not add information for the surgical planning.…”

“…In this study, IED were recorded in 75% of the patients and in 58% a BOLD signal change was observed. These results are in line with the previous EEG-fMRI studies, confirming that a major limitation for the use of the technique in the presurgical setting in TLE patients is the low numbers of IEDs recording during EEG-fMRI (10), and in particular, for mesial TLE, which often generates infrequent scalp-detectable IEDs (31).…”

Mapping Epileptic Networks Using Simultaneous Intracranial EEG-fMRI

“…Scalp EEG-fMRI studies have shown that IED-related BOLD changes in EZ can predict good postsurgical outcome (9,13,14,(22)(23)(24)(25)(47)(48)(49). One of the limiting factors for these studies has been low sensitivity of scalp EEG to capture the whole spectrum of epileptiform activity that can be revealed by invasive recordings (50,51).…”

Localization of interictal discharge origin: A simultaneous intracranial electroencephalographic–functional magnetic resonance imaging study

“…This can be difficult to accurately identify prior to surgery, yet better localization may improve surgical planning, and in turn improve outcomes. 1 Over the past 20 years, simultaneous scalp electroencephalographic (EEG)-functional magnetic resonance imaging (fMRI) has become a noninvasive tool to localize blood oxygen level-dependent (BOLD) responses to focal interictal epileptiform discharges (IEDs). [2][3][4] The overall pattern of BOLD signal changes has been suggested to reflect the network involved in the propagation of IEDs, 5 and the maximal BOLD cluster to indicate the area generating the IED, which has been termed "the spike onset zone."…”

“…For patients with drug‐resistant focal epilepsy undergoing evaluation for epilepsy surgery, it is critical to accurately localize the epileptogenic zone. This can be difficult to accurately identify prior to surgery, yet better localization may improve surgical planning, and in turn improve outcomes 1 . Over the past 20 years, simultaneous scalp electroencephalographic (EEG)–functional magnetic resonance imaging (fMRI) has become a noninvasive tool to localize blood oxygen level‐dependent (BOLD) responses to focal interictal epileptiform discharges (IEDs) 2–4 .…”