Survival Outcome and Prognostic Factors in Patients with Insular Gliomas Undergoing Intraoperative Awake Brain Mapping

Introduction: Insular glioma is one of the most challenging brain tumors to remove, because it is located deep within the frontal, temporal, and parietal operculum and involves the middle cerebral artery, lenticulostriate artery, insular artery, and language-associated subcortical fibers such as the arcuate fasciculus and inferior fronto-occipital fasciculus. In this study, we evaluated the outcomes and prognostic factors of the treatment of insular gliomas that underwent awake surgery and were classified according to the WHO 2021 classification of brain tumors.

Methods: Of the 201 patients who underwent awake surgery at our university hospital from December 2012 to January 2021, we analyzed 36 consecutive cases of insular gliomas based on the WHO 2021 classification of brain tumors.

Results: The mean age was 44.2 years. 23 cases were classified as lower-grade glioma (LrGG), IDH-mutant, grade 2 or 3, and 13 cases as glioblastoma (GBM), IDH-wildtype, grade 4. Among GBM, 5 cases of molecular GBM with TERT promoter mutation were included. The median final extent of tumor resection rate was 87.3%, and more than 90% resection was achieved in 16 patients (44.4%). Regarding the percentage of basal ganglia invasion, molecular GBM and histologically GBM were found significantly more frequently (80.0% and 62.5%) compared to LrGG, IDH-mutant (4.3%). Median survival OS was significantly better in LrGG, IDH-mutant (not reached) compared to molecular GBM (14.5 months) and histologically GBM (11.6 months) (p=0.000) (Figure 1). Cox regression analysis of factors affecting OS showed that 1) histologically GBM (HR 6.41, p = 0.04), 2) having IDH mutation (HR 0.04, p = 0.01), and 3) >90% removal (HR 0.12, p = 0.04) were significant factors (Table 1).

Conclusion : The prognosis of GBM, IDH-wildtype, including molecular GBM with strong basal ganglia infiltration, is severe. However, aiming for a high degree of removal of 90% or more may lead to a longer life expectancy for LrGG and IDH-mutant tumors.