Multimodal Approach to Epilepsy Surgery: The Power of Pairing 7T MRI with SEEG

By Olesya Grinenko, MD, PhD, and Imad M. Najm, MD

History and presentation

A 33-year-old right-handed man was referred to Cleveland Clinic Epilepsy Center for evaluation for epilepsy surgery to treat multidrug-resistant seizures that he’d had since age 9 years. He had no history of childhood febrile seizures, CNS infections or head trauma, and his birth had followed a normal pregnancy and delivery. Most of his seizures occurred without aura or other warning: He would lose consciousness and experience repetitive movements of the arms and legs.

Presurgical evaluation

He underwent extensive presurgical evaluation to characterize his seizures and localize the epileptogenic zone.

Prolonged video-scalp EEG recordings in our epilepsy monitoring unit revealed a seizure semiology compatible with temporal-perisylvian epilepsy, along with scalp EEG features (both interictal and ictal patterns) consistent with a right frontotemporal lobe epilepsy (Figure 1).

Figure 1. EEG showing a seizure initiating in the right temporal region.

3T MRI revealed features suggestive of right hippocampal sclerosis — i.e., right hippocampal atrophy, absence of right hippocampal digitations and an increased FLAIR signal in the right hippocampus. FDG-PET scan showed right anteromesial temporal hypometabolism, and ictal SPECT (SISCOM analysis) revealed an ictal hyperperfusion in the anteromesial temporal and insular-perisylvian regions (Figure 2).

Figure 2. Imaging studies showing MRI features characteristic of right hippocampal sclerosis, right temporal hypometabolism on FDG-PET, and hyperperfusion of mesial temporal structures and the insular region (right > left) on ictal SPECT.

Team discussion of the case during our multidisciplinary patient management conference raised concern that the MRI lesion was more extensive and included not only right mesial temporal structures but also the right insular region. Suspicions that the epileptogenic zone was more widespread were also supported by rather atypical seizure semiology for mesial temporal lobe epilepsy.

Advanced imaging with high-field 7T MRI

In addition to standard presurgical evaluation, the patient was invited to participate in a research 7T MRI study, which had been established and approved by Cleveland Clinic’s institutional review board since 2014. The study allowed comparison of 7T MRI results with those of standard 3T MRI currently used in clinical practice.

High-resolution 7T MRI evaluation confirmed the presence of right hippocampal sclerosis. In addition, it revealed a previously unsuspected lesion in the right posterior insula (Figure 3).

Figure 3. A lesion in the right posterior insula (arrows) is visible on 7T MRI but not on 3T MRI.

Discovery of the additional right insular lesion on 7T MRI led to discussion at another patient management conference. In light of the new finding, the group recommended exploration with stereoelectroencephalography (SEEG) electrodes to study the lesion’s role in this patient’s epilepsy.

SEEG evaluation and surgery

Depth electrodes were implanted in the right temporal perisylvian region — sampling the anterior temporal pole, the amygdala, the hippocampal formation, the temporo-occipital junction, the temporal opercular region, the ventral and dorsal insula, and the frontoparietal opercular region — in addition to the posterior perisylvian (ventral parietal/supramarginal gyrus) region.

Prolonged video-SEEG recordings in the epilepsy monitoring unit confirmed the epileptogenicity of the right hippocampus and revealed a second epileptic zone in the right ventral insula (corresponding to the lesion identified on 7T MRI) (Figure 4).

Figure 4. SEEG recordings showing early ictal involvement of the right hippocampus and right posterior insular region.

The SEEG findings led to recommendation of a resection of the right anteromesial temporal and posterior ventral insular structures (Figure 5).

Following an uncomplicated surgical resection and postoperative recovery, the patient has been seizure-free through five months of follow-up.

Figure 5. Left: Preoperative MRI with implanted electrodes (blue) and regions that identified as epileptogenic (red). Right: Postoperative MRI showing the resection, which included the right temporal lobe and right posterior insula.

Conclusion

This case makes clear how the use of high-resolution 7T MRI allows identification of otherwise unrecognized potentially epileptogenic lesions. In the hands of an experienced multidisciplinary epilepsy team, these types of advanced imaging findings can indicate a tailored SEEG depth electrode implantation strategy that leads to highly accurate localization of the epileptic zone(s) and optimization of epilepsy surgery outcomes.

Dr. Grinenko is a research fellow in Cleveland Clinic’s Epilepsy Center, and Dr. Najm is Director of the Epilepsy Center.