The role of stereoelectroencephalography (SEEG) in reevaluation of epilepsy surgery failures

Abstract

Management of patients after initial epilepsy surgical failure is challenging. In this study, we report our experience in using the stereoelectroencephalography (SEEG) method in the reevaluation of patients after initial epilepsy surgical failure. We selected 28 patients examined through SEEG in our department for drug-resistant focal epilepsy following initial epilepsy surgical failure. For each patient, the residual seizure onset zone (rSOZ) as defined by SEEG was classified as either contiguous if the seizure onset zone (SOZ) was focal and close to the surgical cavity (same lobe) or noncontiguous in cases where the SOZ included site(s) distant from the surgical cavity. The rSOZ was defined according to visual analysis of SEEG traces completed by an estimation of the epileptogenicity index (EI). A second surgical procedure was performed in 12 patients (45%). A favorable outcome (Engel class I or II) was obtained in 9/12 patients (6 in Engel class I, 50%). The proportion of patients that had reoperation was higher in the contiguous group (80%) than in the noncontiguous group (22%) (p=0.02). A rSOZ localized in close relation to the initial surgical resection zone (contiguous group) was found in 10 patients (35%). Among them, 8 have since undergone reoperation, and a good outcome (Engel class I) was achieved in 5/8 (63%). A rSOZ involving a distant region from the first surgery was observed in 18 patients (65%) (noncontiguous group). Among them, only 4 have undergone reoperation, leading to a failure in 2 (Engel class III or IV) and a good outcome in 2 (IA). Ten patients had a first standard temporal lobectomy, and in 50% of these cases, the insula was involved in the rSOZ. Stereoelectroencephalography offers a unique way to evaluate the rSOZ at the individual level and thus guide further surgical decision-making. The best results are observed in patients having a focal rSOZ close to the site of the surgical resection in the first surgery.

Long‐term outcomes of reoperations in epilepsy surgery

“…Although surprising, it is becoming a well‐documented effect that culminates from a few reasons. First, with more sophisticated invasive EEG techniques and their reduced morbidity, there is a lower threshold for the use of invasive EEG to evaluate the epileptogenic network for surgical failures . Nonetheless, there are an increasing number of invasive evaluations that do not lead to subsequent resections in recent years .…”

“…First, with more sophisticated invasive EEG techniques and their reduced morbidity, there is a lower threshold for the use of invasive EEG to evaluate the epileptogenic network for surgical failures. 23 Nonetheless, there are an increasing number of invasive evaluations that do not lead to subsequent resections in recent years. 24 Second, there has been a shift in the demographic of the presenting patient population from "straightforward" mesial temporal lobe epilepsies to more complex extratemporal and nonlesional substrates.…”

“…Vaugier et al have hypothesized complex epileptogenic networks and abnormal connectivity as culprits for surgical failures in mislocalizations. 23 Incomplete resections may occur due to inability to visualize the extent of the lesion, making appropriate tools to identify the area of resection a dire necessity. However, the third group of patients continues to remain poorly understood, with no obvious explanation for recurrence.…”

Outcomes of stereoelectroencephalography exploration at an epilepsy surgery center

“…This is lower compared to a previous study reporting the SOZ being close to the previous resection margin at 35% with reoperation rate of 45% with Engel class I outcomes of 50%. 25 Reoperation was performed in nine patients (88%) in our study; but Engel class I outcome was 25%. Two of these patients with previous epilepsy surgery had previous IVEM.…”

Ictal recruitment of anterior nucleus of thalamus in human focal epilepsy

“…The epileptogenicity index (EI) (Bartolomei et al, 2008) has been shown to quantify the epileptogenicity of brain structures and has been validated with clinically identified probable EZ, seizure outcome following surgical resection, and with interictal high-frequency oscillation maps to identify EZ (Roehri et al, 2018;Vaugier et al, 2018). The EI statistically summarizes the spectral and temporal parameters of SEEG signals and relates to the propensity of a brain area to generate low voltage fast discharges.…”