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

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.