Insular epilepsy surgery: lessons learned from institutional review and patient-level meta-analysis

Abstract

OBJECTIVE Insular lobe epilepsy is a challenging condition to diagnose and treat. Due to anatomical intricacy and proximity to eloquent brain regions, resection of epileptic foci in that region can be associated with significant postoperative morbidity. The aim of this study was to review available evidence on postoperative outcomes following insular epilepsy surgery. METHODS A comprehensive literature search (PubMed/MEDLINE, Scopus, Cochrane) was conducted for studies investigating the postoperative outcomes for seizures originating in the insula. Seizure freedom at last follow-up (at least 12 months) comprised the primary endpoint. The authors also present their institutional experience with 8 patients (4 pediatric, 4 adult). RESULTS A total of 19 studies with 204 cases (90 pediatric, 114 adult) were identified. The median age at surgery was 23 years, and 48% were males. The median epilepsy duration was 8 years, and 17% of patients had undergone prior epilepsy surgery. Epilepsy was lesional in 67%. The most common approach was transsylvian (60%). The most commonly resected area was the anterior insular region (n = 42, 21%), whereas radical insulectomy was performed in 13% of cases (n = 27). The most common pathology was cortical dysplasia (n = 68, 51%), followed by low-grade neoplasm (n = 16, 12%). In the literature, seizure freedom was noted in 60% of pediatric and 69% of adult patients at a median follow-up of 29 months (75% and 50%, respectively, in the current series). A neurological deficit occurred in 43% of cases (10% permanent), with extremity paresis comprising the most common deficit (n = 35, 21%), followed by facial paresis (n = 32, 19%). Language deficits were more common in left-sided approaches (24% vs 2%, p < 0.001). Univariate analysis for seizure freedom revealed a significantly higher proportion of patients with lesional epilepsy among those with at least 12 months of follow-up (77% vs 59%, p = 0.032). CONCLUSIONS These findings may serve as a benchmark when tailoring decision-making for insular epilepsy, and may assist surgeons in their preoperative discussions with patients. Although seizure freedom rates are quite high with insular epilepsy treatment, the associated morbidity needs to be weighed against the potential for seizure freedom.

Predictors of outcomes after surgery for medically intractable insular epilepsy: A systematic review and individual participant data meta‐analysis

“…While many meta‐analyses have systematically studied the clinical outcomes and predictors in temporal lobe epilepsy (TLE) and other forms of ETE (eg, frontal, parietal, and occipital lobe epilepsies), only one such study exists for IE. 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 In this regard, Kerezoudis et al performed a recent meta‐analysis of patients undergoing surgery for insular epilepsy that revealed rates of overall seizure freedom (64.3%) and postoperative neurological deficits (43.2%, most of which were transient) comparable to our study. While their assessment is valuable, the overall findings are limited by the fact that the heterogeneity between studies was not accounted for, multivariate analyses were not performed, missing data were not imputed, and predictors of postoperative neurological complications were not evaluated.…”

“…While their assessment is valuable, the overall findings are limited by the fact that the heterogeneity between studies was not accounted for, multivariate analyses were not performed, missing data were not imputed, and predictors of postoperative neurological complications were not evaluated. 80 In addition, no independent predictors of seizure freedom were identified. 80 There are several main findings in the current study: (a) The surgical treatment of drug-resistant IE results in very good seizure freedom rates that are comparable to those obtained with surgery for ETE 43,44,73,78,79,81 ; similar seizure recurrence patterns are also seen, including 79% and 55% postoperative seizure freedom rates at 1 and 5 years respectively; (b) the efficacy-to-permanent deficit profile is favorable, with <1% of patients harboring poor outcome (seizure recurrence and permanent deficit); (c) independent patient-related predictors of seizure recurrence include younger (pediatric) age and cases requiring invasive EEG monitoring; (d) the seizure-free rate following stereotactic ablation procedures (MRgLA or RFA) was significantly lower than following open resective surgery; (e) surgical treatment of IE is associated with a significant rate of neurological complications in just under half of cases (42.5%)-however, the vast majority are transient and <8% of all surgically treated patients exhibit permanent neurological deficits; (f) the most common neurological complication was motor deficit (30.8%); (g) there was no independent predictor of overall neurological deficits, although posterior insulectomy and opercular resection trended toward significance; (h) frontal operculectomy was independently associated with postoperative motor impairment and hemiparesis, and (i) although dominanthemisphere surgery was independently associated with a higher likelihood of postoperative language impairment, none of the patients who underwent surgery on the dominant side exhibited permanent dysphasia.…”

“…In this regard, Kerezoudis et al performed a recent meta‐analysis of patients undergoing surgery for insular epilepsy that revealed rates of overall seizure freedom (64.3%) and postoperative neurological deficits (43.2%, most of which were transient) comparable to our study. While their assessment is valuable, the overall findings are limited by the fact that the heterogeneity between studies was not accounted for, multivariate analyses were not performed, missing data were not imputed, and predictors of postoperative neurological complications were not evaluated 80 . In addition, no independent predictors of seizure freedom were identified 80 …”

“…While their assessment is valuable, the overall findings are limited by the fact that the heterogeneity between studies was not accounted for, multivariate analyses were not performed, missing data were not imputed, and predictors of postoperative neurological complications were not evaluated 80 . In addition, no independent predictors of seizure freedom were identified 80 …”

Commentary: Interictal High Gamma Oscillation Regularity as a Marker for Presurgical Epileptogenic Zone Localization

“…Is there a role of this method for insular or cingulate seizures which are notoriously harder to localize, given the depth of these structures? 19,20 4. Does regularity of interictal gamma oscillations represent the same phenomena in different brain regions, eg, the primary visual vs motor cortex?5.…”