Maximum safe resection of insular gliomas: update on surgical outcomes from 500 cases

OBJECTIVE: Insular gliomas present a unique surgical challenge due to their location near critical vascular structures and proximity to functional brain regions. While different surgical approaches to insular tumors exist, language and motor stimulation mapping are critical for a transcortical approach. The aim of this study was to determine if the transcortical approach to resection of insular gliomas remains a safe and effective strategy by assessing tumor characteristics, surgical outcomes, and postoperative functional outcomes in patients with newly diagnosed or recurrent tumors. METHODS: This retrospective analysis included 502 newly diagnosed and recurrent low-grade gliomas (LGGs) and high-grade gliomas (HGGs) of the insula (in 394 unique patients) resected between September 1997 and December 2022 at a single center. Tumors were classified based on the Berger-Sanai zone schema, and contrast-enhancing and non-contrast-enhancing tumor volumes were manually segmented on MRI and used to calculate the extent of resection (EOR). Patient morbidity was assessed at multiple time points from the initial presentation to at least 6 months of follow-up. Progression-free survival (PFS) and overall survival (OS) were compared between subgroups using unadjusted and propensity score-adjusted Kaplan-Meir and Cox regression analyses. RESULTS: Overall, 316 (165 LGG, 151 HGG) newly diagnosed and 186 (69 LGG, 117 HGG) recurrent cases were included. Grade 2 gliomas were typically larger than grade 4 IDH-wildtype gliomas (43 cm3 vs 17.5 cm3, p < 0.001). Persistent postoperative motor and language deficits occurred in < 4% of cases with newly diagnosed grade 2 tumors, although transient deficits occurred more frequently (9.5% of cases with transient motor deficit and 20% of cases with transient language deficit). For patients with newly diagnosed grade 2 insular gliomas, OS was improved when the residual tumor volume was < 2.7 cm3. Minimizing residual tumor volume was also associated with prolonged PFS and OS for recurrent grade 2 insular gliomas. Similarly, contrast-enhancing tumor EOR > 88.6% was associated with improved PFS and OS for patients with newly diagnosed IDH-wildtype glioblastoma. Overall, surgical and medical complications occurred in < 3% of cases. Finally, new permanent arm or leg weakness was significantly associated with worse OS in multivariable analyses (HR 2.06, 95% CI 1.14-3.74; p = 0.017). CONCLUSIONS: Maximum safe resection using a transcortical approach and cortical and subcortical mapping continues to be a robust surgical strategy with low surgical morbidity for patients with newly diagnosed and recurrent insular gliomas.