Insular glioma resection: assessment of patient morbidity, survival, and tumor progression

Clinical article

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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.

Abbreviations used in this paper: EOR = extent of resection; HGG = high-grade glioma; HR = hazard ratio; KPS = Karnofsky Performance Scale; LGG = low-grade glioma; MPFS = malignant progression–free survival; OS = overall survival; PFS = progression-free survival.

Article Information

Address correspondence to: Mitchel S. Berger, M.D., Department of Neurological Surgery, University of California, San Francisco, 505 Parnassus Avenue, M779, Box 0112, San Francisco, California 94143. email: Bergerm@neurosurg.ucsf.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Drawings depicting patient positioning and the microsurgical technique for transcortical resection of an insular glioma. For tumors primarily above the sylvian fissure (A, inset), the head is tilted 15° above the horizontal; it is tilted 15° below the horizontal (B, inset) for tumors primarily below the sylvian fissure. After cortical mapping reveals areas of nonfunctional cortex, a series of cortical windows (C) are made above and below the sylvian fissure. Tumor resection (D) traces the course of the uncinate fasciculus, eventually connecting the supra- and infrasylvian windows. Lenticulostriate arteries (E) are identified at the medial margin of resection, along which the internal capsule can be subcortically stimulated. MCA = middle cerebral artery.

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    Illustrations showing the Berger-Sanai insular glioma classification system. A: Zones I–IV are divided along the line of the sylvian fissure and a perpendicular plane crossing the foramen of Monro. B: Insular tumor location is determined by the location of the majority of the tumor mass. C: Axial illustrations of Zones I and IV, located anterior to the foramen of Monro, and Zones II and III, located behind the foramen of Monro.

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    Preoperative axial T2-weighted and sagittal T1-weighted MR images showing Zones I–IV of the Berger-Sanai insular glioma classification system. Giant tumors are lesions that occupy all 4 zones.

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    Kaplan-Meier curve demonstrating OS of patients with insular glioma, based on histological grade.

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    Kaplan-Meier curves revealing the OS of patients with Grade II (left) or III (right) insular gliomas, stratified by EOR.

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    Kaplan-Meier curve demonstrating PFS by insular glioma histological grade.

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    Kaplan-Meier curves showing PFS of patients with Grade II (left) or III (right) insular gliomas, stratified by EOR.

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    Kaplan-Meier curve demonstrating MPFS of patients with Grade II insular gliomas, stratified by EOR.

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