Safety of Intrahippocampal Depth Electrodes for Presurgical Evaluation of Patients with Intractable Epilepsy

Abstract

Summary:Purpose: Intracerebral depth electrodes are used in preoperative evaluation of selected patients with intractable epilepsies. In spite of their usefulness, safety of depth electrodes is disputed, and the number of insertions is decreasing. This study examined retrospectively possible deleterious effects such as perioperative complications, induction of epileptogenesis, and neuropsychologic deficits.Methods: Clinical course and neuroradiologic findings of 1 15 patients with bilaterally inserted longitudinal intrahippocampal depth electrodes (IDEs) were analyzed. Hippocampal resection specimens were examined histopathologically. To detect newly developed epileptogenic areas, EEG recordings, seizure control, and semiology after standardized resection procedures were compared between patients who received IDEs and those who did not. To demonstrate functional deficits caused by IDE insertion into an unaffected hippocampus of the speech-dominant hemisphere, changes of verbal learning and memory performances before and after right amygdalohippocampectomy were compared between patients evaluated with and without IDEs.Results: Five significant complications without any permanent neurologic deficit were noted, and only one was specifically linked to IDE insertion. The tissue damage associated with the insertion was minimal and sharply circumscribed. No differences of seizure outcome after standardized resections were identified between patients with and without IDEs. In postoperative EEG recordings, there was no evidence of new epileptogenic areas. No verbal memory deficit caused by IDE implantation into the hippocampus of the speech-dominant hemisphere was detectable.Conclusions: Results indicate that it is safe to implant these IDEs in selected patients. Key Words: Epilepsy surgerySafety-Depth electrodes-Memory-Hippocampus.Two thirds to three quarters of presurgical evaluation protocols use intracerebral depth electrodes (IDES) (1,2).The usefulness of depth electrodes has been well documented (3-10). Specifically, the aim of tailored resections with better neuropsychologic outcome demonstrates their increasing necessity (1 1,12). However, because of current budget cuts and the presumed risks, the number of depth-electrode insertions is decreasing. The main safety considerations are concerned with a higher rate of complications or with the possible induction of new epileptogenic zones. Furthermore, functional deficits may result from structural damage, especially if electrodes are inserted into a brain area that will not be resected (8,lO). All reports on safety profiles of depth electrodes have been limited to the assessment of neurologic complications and imaging findings (3,8,10,(13)(14)(15) in our series, all patients received depth electrodes inserted longitudinally into each hippocampus (Fig. 1).The hippocampus is one of the most vulnerable brain areas with respect to epileptogenesis, and its role in processing of declarative memory can be adequately measured by neuropsychological testing (1 l, 16-1 8). The...

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Integration of EEG, MRI, and SPECT in Localizing the Seizure Focus for Epilepsy Surgery

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