Technical NoteCombining stereo-electroencephalography and subdural electrodes in the diagnosis and treatment of medically intractable epilepsy
Introduction
Stereo-electroencephalography (SEEG) has become one of the standard invasive procedures for exploring the epileptic cortex, especially deep-located epileptic foci [1], [2], [3], [4], [5]. This method has advantages including mapping ictal onset and seizure propagation, sampling deep cortical regions, and a relatively low complication rates [2], [3]. Nevertheless, SEEG can only sample isolated cortical areas from the brain and is limited by the location or number of implanted electrodes. The spatial limitation of this technique and the relative inferiority of its functional mapping abilities along with the lack of recording contiguous cortical regions may cause difficulties in the precise anatomical delineation between the epileptogenic zone and functional cortex [4]. This limitation can be partially overcome by the use of subdural electrodes, which provide meticulous contiguous mapping of the cortex due to the continuity of its contacts. Taking into account these limitations, we combined both SEEG and subdural electrode methodology for chronic extraoperative mapping of select patients with medically intractable focal epilepsy. This was performed using the hybrid technique of both SEEG and subdural strip electrode placement.
Section snippets
Implantation technique
The depth and strip electrode targeting and trajectory are determined using robotic stereotactic software (ROSA; Medtech, Montpellier, France) based on a pre-implantation hypothesis regarding the possible location of the epileptogenic zone. Preoperative contrasted volumetric T1-weighted MR images are acquired and loaded into this robotic system. The planned trajectories are meticulously reviewed to avoid major vessel injury and collisions between the two types of electrodes. If so the
Patient 1
A 19-year-old ambidextrous woman was referred for pharmacoresistant epilepsy. Her seizures had started at 7 years of age and were characterized by auditory auras followed by consciousness impairment and generalized tonic-clonic seizures with right head version. Scalp video electroencephalography (EEG) monitoring revealed interictal sharp waves in the left posterior temporal, occipital and right fronto-temporal regions. EEG ictal patterns were non-localizable. Brain MRI (1.5 T) was within normal
Discussion
We performed SEEG evaluations combined with strip electrode placements in four patients. As SEEG has a limited ability to record contiguous cortical regions of epileptogenic and functional cortex, the precise anatomical delineation between these two regions can be difficult. In these patients, the additional subdural strip electrodes provided (1) information regarding the precise description of seizure spread in the cortical surface adjacent to the subdural space, (2) identification of
Conclusion
The combination of SEEG and subdural strip electrodes provides additional and complementary information regarding functional mapping and the detection of seizure onset. This hybrid technique provides additional data, which cannot be obtained by either of the techniques when applied separately, offering superior understanding of the dynamics of the epileptic activity and its interaction with functional cortical areas. In order to validate this technique, a larger series of patients will be
Conflicts of Interest/Disclosures
The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.
References (11)
- et al.
The use of subdural grids in the management of focal malformations due to abnormal cortical development
Neurosurg Clin N Am
(2002) - et al.
Functional stereotaxic exploration (SEEG) of epilepsy
Electroencephalogr Clin Neurophysiol
(1970) - et al.
Stereoelectroencephalography in the presurgical evaluation of focal epilepsy: a retrospective analysis of 215 procedures
Neurosurgery
(2005) - et al.
Stereoelectroencephalography: surgical methodology, safety, and stereotactic application accuracy in 500 procedures
Neurosurgery
(2013) - et al.
Stereoelectroencephalography in the “difficult to localize” refractory focal epilepsy: early experience from a north American epilepsy center
Epilepsia
(2013)