Insular glioma resection: assessment of patient morbidity, survival, and tumor progression
Authors: Sanai Nader , Polley Mei-Yin , Berger Mitchel S. 
Published: July 2009

Object
Insular gliomas remain surgically challenging cases due to complex anatomy, including surrounding vasculature and the relationship to functional structures. To define the morbidity profile associated with aggressive insular glioma removal as well as its impact on long-term outcome, the authors retrospectively evaluated the extent of resection (EOR) in the context of this complex anatomy and function and assessed its role in determining disease progression, malignant transformation, and, ultimately, patient survival.

Methods
The study population included adults who had undergone initial or repeat resection of insular gliomas of all grades. Tumor location was identified according to a proposed quadrant-style classification (Zones I–IV) of the insula. Low- and high-grade gliomas were volumetrically analyzed using FLAIR and contrast-enhanced T1-weighted MR imaging, respectively.

Results
One hundred fifteen procedures involving 104 patients with insular gliomas were identified. Patients presented with low-grade gliomas (LGGs) in 70 cases (60%) and high-grade gliomas (HGGs) in 45 (40%). Zone I (anterior-superior) was the most common site within the insula (40 patients [39%]), followed by Zone I+IV (anteriorsuperior + anterior-inferior; 26 patients [25%]). The median EOR was 82% (range 31–100%) for low-grade lesions and 81% (range 47–100%) for high-grade lesions. Zone I was associated with the highest median EOR (86%), and among all lesion grades, the insular quadrant anatomy was predictive of the EOR (p = 0.0313). Overall, there were 16 deaths (15%) during a median follow-up of 4.2 years. There were no surgery-related deaths, and new, permanent postoperative deficits were noted in 6 patients (6%). Among LGGs, tumor progression and malignant transformation were identified in 20 (29%) and 14 cases (20%), respectively. Among HGGs, progression was identified in 16 cases (36%). Patients with LGGs resected ≥ 90% had a 5-year overall survival (OS) rate of 100%, whereas those with lesions resected < 90% had a 5-year OS rate of 84%. Patients with HGGs resected ≥ 90% had a 2-year OS rate of 91%; when the EOR was < 90%, the 2-year OS rate was 75%. The EOR was predictive of OS both in cases of LGGs (hazard ratio [HR] 0.955, 95% CI 0.921–0.992, p = 0.017) and HGGs (HR 0.955, 95% CI 0.918–0.994, p = 0.024). Progression-free survival (PFS) was also predicted by the EOR in both LGGs (HR 0.973, 95% CI 0.948–0.998, p = 0.0414) and HGGs (HR 0.958, 95% CI 0.919–0.999, p = 0.0475). Interestingly, among patients with LGGs, malignant progression was also significantly associated with a lower EOR (HR 0.968, 95% CI 0.393–0.998, p = 0.0369).

Conclusions
Aggressive resection of insular gliomas of all grades can be accomplished with an acceptable morbidity profile and is predictive of improved OS and PFS. Among insular LGGs, a greater EOR is also associated with longer malignant PFS. Data in this study also suggest that insular gliomas generally follow a more indolent course than similar lesions in other brain regions.