Impact on Awake Mapping on Overall Survival and Extent of Resection in Patients With Adult Diffuse Gliomas Within or Near Eloquent Areas: A Retrospective Propensity Score-matched Analysis of Awake Craniotomy Vs. General Anesthesia

DOI: https://doi.org/10.21203/rs.3.rs-377735/v1

Abstract

Introduction: Awake craniotomy (AC) with intraoperative mapping is the best approach to preserve neurological function for glioma surgery in eloquent or near eloquent areas, but whether AC improves the extent of resection (EOR) is controversial. Furthermore, there is less evidence of improved overall survival (OS) in glioma patients. This study aimed to compare the long-term clinical outcomes of glioma resection under AC with those under general anesthesia (GA).

Methods: Data of 335 patients who underwent surgery with intraoperative magnetic resonance imaging for newly diagnosed gliomas of World Health Organization (WHO) grades II-IV between 2000 and 2013 were reviewed. EOR and OS were quantitatively compared between the AC and GA groups after 1:1 propensity score matching. The two groups were matched for age, preoperative Karnofsky performance status, tumor location, and pathology based on the WHO 2007 classification.

Results: After propensity score matching, 91 pairs were obtained. The median EOR were 96.1% (interquartile range [IQR] 7.3) and 97.4% (IQR 14.4) in the AC and GA groups, respectively (p=0.31). The median survival times were 163.3 months (95% confidence interval [CI] 77.9-248.7) and 143.5 months (95% CI 94.4-192.7) in the AC and GA groups, respectively (p=0.585).

Conclusions: Even if the glioma was within or close to the eloquent area, AC was comparable with GA in terms of EOR and OS. In case of difficulties in randomizing patients with eloquent or near eloquent glioma, our propensity score-matched analysis provides retrospective evidence that AC can obtain EOR and OS equivalent to removing glioma under GA.

Introduction

Diffuse glioma surgery must balance neurological function preservation with maximization of tumor removal. Amassing evidence has shown that removal rates correlate with prognosis regardless of glioma World Health Organization (WHO) grade.[16] Studies have advocated that the extent of resection (EOR) beyond the removal target on magnetic resonance imaging (MRI) also improves prognosis.[710] This cytoreductive idea is derived from the infiltrative nature of gliomas. However, brain tissue removal with low tumor density is likely to decrease neurological function. Since the resection range cannot be drawn image-wise, there is no choice but to draw the resection range by awake craniotomy with intraoperative mapping (AC). Has AC improved the EOR and overall survival (OS)? The essential language and motor functions have been at the core of functional preservation efforts.[11] AC is the most suitable language/motor functional preservation method. Although there is little objection that AC is superior to general anesthesia (GA) for functional preservation, its ability to improve the EOR is controversial.[1227] One reason making such validation difficult is that many studies have not evaluated the OS, despite the proven strong correlation between EOR and OS, owing to the difficulty of adjusting the bias induced by the eloquent areas. The lack of an objective definition of eloquent areas on the image is a factor, but the most critical one is the selection bias of patients who underwent surgery performed under GA despite eloquent lesions. Patients who undergo GA may have aphasia and paralysis or are elderly individuals, which also cause poor OS. Only randomized controlled trials (RCTs) can eliminate these unavoidable selection biases in patients with eloquent glioma in the GA group. However, the superiority of AC in functional preservation has been established, and RCT planning has high ethical hurdles. Therefore, we believe that propensity score-matched analysis (or pseudo-randomization) is the best method to examine the effects of AC on EOR and OS while adjusting for treatment selection bias. To our best knowledge, our propensity score-matched analysis comparing AC and GA is the first and largest study to quantitatively evaluate EOR and OS. This study aimed to compare the long-term clinical outcomes of glioma resection under AC with those under GA.

Methods

Patient Selection

The inclusion criteria were (1) newly diagnosed glioma, including oligodendroglioma, diffuse astrocytoma, anaplastic oligodendroglioma, anaplastic astrocytoma, oligoastrocytoma, anaplastic oligoastrocytoma, and glioblastoma, based on the WHO 2007 classification; (2) surgical resection with low-field intraoperative magnetic resonance imaging (iMRI) from July 2000 to December 2013; and (3) age ≥ 18. The exclusion criteria were biopsy and incomplete intraoperative MRI data to calculate volumetry. Our indication of AC complies with the Japanese AC guidelines.[28] A precentral gyrus tumor is an absolute indication for AC,[29] and other tumors near the pyramidal tract are relative indications. Combined use of AC and motor evoked potential (MEP) monitoring improves the robustness of motor function monitoring and reduces the risk of permanent paralysis,[30] and we are actively performing AC except in cases where paralysis has already appeared before surgery. The language-dominant hemisphere is determined by referring to the dominant hand and functional MRI (fMRI).[31] Right-handedness and left lesion near the language network constitute an absolute indication. If aphasia occurs during preoperatively, AC is not performed because language mapping in AC is difficult.

AC

All patients received sleep-awake-sleep protocol anesthesia. First, craniotomy was performed under GA using a supraglottic airway device. Then, the first iMRI was performed. The patient was then awakened, and cortical mapping was used to identify language and motor areas. Tumors were removed by performing appropriate cortical/subcortical mapping with a positive mapping strategy. After evaluating the brain tumor’s resection on a second MRI, the scalp was closed under mild sedation without intubation. An Ojemann cortical bipolar stimulator (OCS-1; Interga Radionics, Inc.) was used for cortical stimulation (repetitive square-wave biphasic currents of alternating polarity; intensity, 0–6 mA [biphasic currents 0–12 mA]; frequency, 50 Hz; duration, 2 s; interpolar distance, 5 mm). The distance between the stimulation sites was 5–10 mm, and a surface electroencephalogram (bandpass filter of 10 Hz to 1.5 kHz) was recorded to detect epileptic seizures.

Intraoperative MRI-guided surgery

MR images were obtained using iMRI (0.3-T AIRIS II™ Hitachi Medical, Chiba, Japan). The first intraoperative MR image was obtained after a dural incision to minimize the effects of brain shift. Sequential iMRI was performed before duraplasty to allow repeated resection of the residual tumor. The final iMR image was obtained after achieving the best possible resection. The tumor site, which showed positive findings in the cortex/white matter mapping during AC, was not removed and was preserved even if it remained on intraoperative MRI. A three-dimensional volumetric measurement of the first and final iMRI studies was retrospectively conducted, as previously described.[3, 4, 32] Manual segmentation was performed with the region-of-interest analysis to measure tumor volume based on T2-weighted images in WHO grades II and III and contrast-enhanced T1-weighted MR images in grade IV. If the tumor did not show gadolinium enhancement, the T2 hyperintensity area was measured. EOR was defined as follows: (initial MR tumor volume – final MR tumor volume) / (initial MR tumor volume).

Statistical analysis

Statistical analyses were performed using SPSS Statistics, Version 25.0 (IBM Corp, Armonk, NY, USA). Categorical variables were compared using the chi-square test. The Mann-Whitney U test and t-test were used for continuous nonparametric and parametric variables, respectively. OS analysis was performed using Kaplan-Meier curves and log-rank tests. P-values < 0.05 were considered significant.

Propensity score-matched analysis

To overcome the bias arising from the lack of randomization and heterogeneity of glioma patients, one-to-one matching without replacement was performed using the nearest-neighbor match on the logit of the propensity score with caliper width set to 0.2 times the standard deviation of the logit of the propensity score. The distribution of each characteristic mentioned below in the two groups was assessed with the standardized mean difference, calculated as the difference in the means or proportions of a variable divided by the pooled estimate of its standard deviation.[33] Standard mean difference < 0.1 between the two groups was considered an adequate balance of matching.[34] Propensity score matching was conducted using age, preoperative Karnofsky performance scale (KPS) score, pathology based on the WHO 2007 classification, and tumor location. Age, preoperative KPS, and pathological grade based on the WHO 2007 classification are commonly accepted prognostic factors for adult diffuse gliomas.[35] Most patients with eloquent gliomas underwent surgery under AC, and patients undergoing GA also have a selection bias that affects prognosis because of their relatively low KPS and older age. Few studies have considered eloquent lesions as a prognostic factor. Therefore, we used the tumor’s main region as an alternative variable to investigate the effect of AC on EOR and OS.

Results

Patient’s characteristics

A total of 335 patients who underwent surgery with iMRI for newly diagnosed gliomas of WHO grade II-IV between 2000 and 2013 were analyzed. Patient characteristics are shown in Table 1. Before propensity score matching, patients were significantly older in the AC group than in the GA group (p < 0.001). The male/female ratio was not significantly different (p = 0.499). The left hemisphere, with a high proportion of eloquent lesions, was significantly more affected in the AC group (p < 0.001). The main tumor location in the AC group was the fronto-temporo-parietal cortex, including the insula near the language network and motor pathway (p < 0.001). Grade II-III tumors were predominant over glioblastoma (p < 0.001). The preoperative KPS score was higher in the AC group than in the GA group (p < 0.001), while the preoperative tumor volume was not significantly different between the two groups (p = 0.738).

Analysis after propensity score matching

After matching, no differences were found in the mean age (p = 0.997), tumor location (p = 0.959), pathology (p = 0.966), or mean preoperative KPS (p = 0.722). Moreover, the standardized mean difference results demonstrated negligible or small differences in all characteristics between the two groups.

The adjusted covariates were well balanced in the propensity score-matched cohort with a standardized mean difference of < 0.1 (Table 1), although the proportion of left hemisphere tumors, a factor that was not adjusted, remained higher in the AC group.

Table 1. Patient characteristics and group comparison before and after propensity score matching

 

Before propensity score matching

After propensity score matching

Characteristics

AC

GA

p-value

AC

GA

p-value

Standardized mean difference

No. of patients

113

222

 

91

91

 

 

Age, years (mean±SD)

40.8±12.2

49.2 ±15.7

p<0.001

41.1±12.3

41.4±13.5

0.997

0.002

Male/female sex

70/43

129/93

0.499

59/32

50/41

0.173

0.203

Side of the tumor (right/left)

23/90

124/88

p<0.001

19/72

57/32

p<0.001

0.970

Main location, number (%)

 

 

p<0.001

 

 

0.959

0.081

   Frontal lobe

82 (73)

90 (41)

 

62 (68)

59 (65)

 

 

   Temporal lobe

11 (10)

43 (19)

 

10 (11)

12 (13)

 

 

   Insula

11 (10)

24 (11)

 

10 (11)

11 (12)

 

 

   Parietal lobe

9 (8)

38 (17)

 

9 (10)

9 (10)

 

 

   Occipital lobe

0 (0)

12 (5)

 

0 (0)

0 (0)

 

 

   Basal ganglia

0 (0)

2 (1)

 

0 (0)

0 (0)

 

 

   Thalamus

0 (0)

4 (2)

 

0 (0)

0 (0)

 

 

   Corpus callosum

0 (0)

3 (1)

 

0 (0)

0 (0)

 

 

   Brainstem

0 (0)

4 (2)

 

0 (0)

0 (0)

 

 

   Cerebellum

0 (0)

2 (1)

 

0 (0)

0 (0)

 

 

2007 WHO grade, number (%)

 

 

p<0.001

 

 

0.987

0.024

  WHO grade II

53 (47)

52 (23)

 

39 (43)

40 (44)

 

 

  WHO grade III

46 (41)

65 (29)

 

38 (42)

37 (41)

 

 

  WHO grade IV

14 (12)

105 (47)

 

14 (15)

14 (15)

 

 

2007 WHO classification, number (%)

 

 

p<0.001

 

 

0.966

0.176

  Glioblastoma

14 (12)

105 (47)

 

14 (15)

14 (15)

 

 

  Anaplastic astrocytoma

13 (12)

29 (13)

 

12 (13)

12 (13)

 

 

  Anaplastic oligodendroglioma

19 (17)

14 (6)

 

14 (15)

13 (14)

 

 

  Anaplastic oligoastrocytoma

14 (12)

22 (10)

 

12 (13)

12 (13)

 

 

  Diffuse astrocytoma

13 (12)

12 (5)

 

6 (7)

9 (10)

 

 

  Oligodendroglioma

23 (20)

25 (11)

 

19 (21)

21 (23)

 

 

  Oligoastrocytoma

17 (15)

15 (7)

 

14 (15)

10 (11)

 

 

Median preoperative KPS [IQR]

100 [10]

90 [20]

p<0.001

100 [10]

100 [10]

0.633

0.002

Mean preoperative tumor volume, cm3 (mean±SD)

45.5±37.6

44.0±39.4

0.738

44.4±39.0

42.9±41.0

0.722

<0.001

AC, awake craniotomy; GA, general anesthesia; IQR, interquartile range; KPS, Karnofsky performance status; SD, standard deviation

Post-hoc analysis for prognostic factors

Isocitrate dehydrogenase (IDH) mutation and 1p19q codeletion status were examined in the cohorts after propensity score matching. In 26 cases, the 1p19q status could not be identified. However, the percentage of 1p19q codeletion was not significantly different between the groups (Table 2; p = 0.397). The IDH status of 16 individuals was unknown, but no significant difference was found in the prevalence of IDH mutations (Table 2; p = 0.131). We also examined the proportion of patients who received radiation therapy and chemotherapy in the two groups, finding no significant differences in nimustine hydrochloride or temozolomide usage (p = 0.741) nor in the administration of radiation therapy (Table 2; p = 0.532).

Table 2

Glioma prognostic factors in propensity-matched cases.

 

AC

GA

p Value

No. of patients

91

91

 

1p19q status, number (%)

   

0.397

Codeletion

39 (43)

39 (43)

 

Non-codeletion

42 (46)

36 (40)

 

N. D.

10 (11)

16 (18)

 

IDH status, number (%)

   

0.131

IDH-mutated

66 (73)

64 (70)

 

IDH-wildtype

14 (15)

22 (24)

 

N. D.

11 (12)

5 (5)

 

Chemotherapy, number (%)

   

0.741

ACNU-based

44 (48)

39 (42)

 

TMZ

10 (11)

12 (13)

 

None

37 (40)

40 (43)

 

Radiation therapy, number (%)

   

0.532

Yes

62 (68)

58 (63)

 

No

29 (32)

33 (36)

 
AC, awake craniotomy; GA, general anesthesia; ACNU, nimustine hydrochloride; TMZ, temozolomide; IDH, isocitrate dehydrogenase
N.D., not determined

EOR, postoperative KPS, and OS

The EOR calculated by volumetry and the KPS scores are shown in Table 3. The median removal rates were 96.1% and 97.4% in the AC group and GA group, respectively, showing no significant difference. Three months after surgery, the median KPS values in both groups decreased by 10 points compared with the preoperative values. Interestingly, KPS scores did not decrease in grade II tumors but decreased the most in the grade IV GA group (Table 3; p = 0.137). The median survival time was not significantly different between the AC (163.3 months) and GA (143.5 months) groups (Fig. 1.A). Although the median survival time could not be calculated for grade II patients, the mean survival time was 143.4 months (95% CI 125.2-161.7) in the AC group and 135.8 months (95% CI 121.0-150.6) in the GA group, without significant difference (Fig. 1.B). No significant difference was found in the median survival of grade III patients between the AC group (163.3 months, 95% CI 150.0-176.7) and the GA group (143.5 months, 95% CI 81.0-206.1; Fig. 1.C). No significant difference was observed in the median survival of grade IV patients between the AC group (30.4 months, 95% CI 23.9–36.9) and the GA group (16.0 months, 95% CI 2.7–29.2; Fig. 1.D).

Table 3

Clinical outcomes in the propensity-matched cases.

 

AC

GA

p Value

EOR, %, median [IQR]

     

Total

96.1 [17.3]

97.4[14.4]

0.310

WHO grade II

92.8 [14.1]

93.4 [18.7]

0.965

WHO grade III

94.3 [31.9]

98.4 [13.5]

0.108

WHO grade IV

100 [0.48]

100 [1.1]

0.982

EOR, %, mean ± SD [95% CI]

     

Total

85.8 ± 22.0 [81.2–90.4]

89.0 ± 17.5 [85.3–92.6]

0.277

WHO grade II

84.8 ± 22.2 [77.6–92.0]

85.3 ± 19.4 [79.1–91.5]

0.916

WHO grade III

81.7 ± 24.0[73.8–89.6]

89.6 ± 17.4 [83.8–95.4]

0.107

WHO grade IV

99.5 ± 1.0 [95.1-100.6]]

97.9 ± 4.8 [95.1-100.6]]

0.231

Preoperative KPS, median [IQR]

     

Total

100 [10]

100 [10]

0.633

WHO grade II

100 [10]

100 [0]

0.528

WHO grade III

100 [10]

100 [10]

0.827

WHO grade IV

90 [10]

90 [13]

0.804

KPS 3 months after surgery, median [IQR]

     

Total

90 [20]

90 [20]

0.384

WHO grade II

100 [10]

100 [10]

0.354

WHO grade III

90 [20]

90 [30]

0.221

WHO grade IV

90 [25]

80[32.5]

0.137

AC, awake craniotomy; GA, general anesthesia; KPS, Karnofsky performance status; IQR, interquartile range; EOR, extent of resection; IDH, isocitrate dehydrogenase; SD, standard deviation; CI, confidence interval

Discussion

In a comparative study of GA and AC, the largest analysis was performed with the prognostic factors adjusted by propensity score. This study showed that AC for eloquent glioma was comparable with GA in terms of EOR and OS.

Superiority in propensity score-matched analysis for bias adjustment

We compared our study to previous articles comparing AC versus GA-adjusted background factors (Table 4). When considering the effect of AC on OS, it is challenging to consider a control group for AC other than GA. However, in retrospective or prospective designs, there will always be significant differences between the characteristics of patients undergoing AC and GA. The AC group had better KPS score and younger age before propensity score matching (Table 1). The same table also shows that lower-grade cases are biased toward AC, inevitably implying that cases with good prognosis are biased toward the AC group. The most direct way to establish effectiveness of AC is to randomize patients with glioma near eloquent areas. Only one RCT concluded that removal rate and functional preservation were significantly worse in the AC group.[26] As that the superiority of AC in terms of functional preservation has become commonly accepted, it is becoming challenging to implement RCTs ethically. To our knowledge, only one RCT is planned for glioblastoma.[36] The selection criteria include the condition that the neurosurgeon can remove the tumor in both surgical procedures, cleverly avoiding ethical issues. We considered propensity score-matched analysis as the most suitable for examining the effects of AC on OS in a retrospective analysis.

Table 4

Studies comparing patients undergoing awake craniotomy (AC) vs general anesthesia (GA) after bias adjustment

Study

Object

Study design

(bias adjustment)

No. of patient

AC, GA

EOR

AC vs GA

OS

Functional preservation

Suarez-Meade et al., 202012

 

Review meta-analysis

437, 1892

AC > GA

90.1% vs 81.7% (p = 0.06)

n.a.

AC = GA

Bu et al., 202013

 

Review meta-analysis

499, 334

AC > GA

Pooled risk ratio 0.81

n.a.

AC > GA

Brown et al., 201622

 

Review

411, 540

AC < GA

Mean GTR 41%vs 44 %

n.a.

AC > GA

Gerritsen et al., 202016

GIV

Retrospective

(propensity score-matched)

37, 111

AC > GA

94.89% vs 70.30 (p < 0.001)

AC = GA

AC > GA

Eseonu et al., 201719

GII-IV

Retrospective (matched pairs)

27, 31

AC = GA

86.3% vs 79.6% (p = 0.136)

n.a.

AC > GA

Martino et al., 201321

GII

Retrospective (matched pairs)

11, 11

AC > GA

91.7% vs 48.7% (p = 0.001)

n.a.

AC > GA

Duffau et al., 200527

GII

Retrospective (chronological comparison)

100, 122

AC > GA

GTR rate 21.6% vs 6.0%

AC > GA

AC > GA

Pichierri et al., 201915

GII-IV

Retrospective (matched pairs)

20, 26

AC = GA

GTR rate 60.0% vs 53.8%

AC > GA

AC > GA

Tuominen et al., 201320

GI-IV

Retrospective (matched pairs)

20, 20

AC = GA

GTR rate 50.0% vs 55.0%

n.a.

AC > GA

This study

GII-IV

Retrospective

(propensity score-matched)

91, 91

AC = GA

96.1% vs. 97.4% (p = 0.83)

AC = GA

AC = GA

AC, awake craniotomy; G, WHO grade; GA, general anesthesia; KPS, Karnofsky performance status; OS, overall survival; RCT, randomized controlled study; IQR, interquartile range; EOR, extent of resection; n.a., not available; GTR, gross total resection

EOR and OS

There is much debate on whether AC improves the resection rate. Some reports have stated that the removal rate is improved,[12, 13, 16, 21, 23, 24, 27] while others reported a decrease or no significant difference.[14, 15, 1820, 22, 26] The best way to address this issue is to confirm that the resection rate correlates with prognosis. Most studies are limited to the analysis of the functional outcome. Gerritsen et al. used propensity score-matched analysis limited to grade IV to show that AC improved EOR, but not OS,[16] and attributed the lack of significance to a sample size issue. Pichierri et al. showed the same resection rate for AC and GA, but better OS with AC[15]: Postoperative neural function might have affected prognosis. Although Sacko et al. evaluated the OS of glioma patients, data from tumors other than glioma were included in the analysis of resection rates.[23] OS data of Duffau et al. and Gravesteijn et al. were not quantitative evaluations using Kaplan-Meier curves.[18, 27] Our data are consistent with the absence of significant differences in EOR and OS between the AC and GA groups, proving the validity of the results.

Difference between AC and GA resection rates

According to Chang et al., a false eloquent area is presumed to be eloquent based on preoperative fluid-attenuated inversion recovery (FLAIR)/T2 imaging but is not eloquent based on the AC mapping.[37] A true eloquent area is presumed to be eloquent based on anatomical preoperative FLAIR/T2 imaging and is confirmed as such by AC mapping. They concluded that AC mapping improved the removal rate and prognosis when the T2/FLAIR tumor area was a false eloquent. By contrast, if it was a true eloquent, the prognosis did not change, and the EOR was the same as in the GA group. Considering the lack of significant difference in KPS scores between the AC and GA groups before and 3 months after surgery in diffuse gliomas including grades II-IV, the lack of difference in AC and GA removal rates suggested that a false eloquent contained more of the iMRI removal target than the true eloquent. In the sub-analysis of grade II gliomas, no difference was found in the removal rate, OS, or postoperative KPS between the two groups (Table 3, Fig. 1.B). Our data suggest that there was little true eloquence in the grade II T2 regions. Grade IV sub-analysis showed no difference in EOR, but KPS scores tended to be superior in the GA group than in the AC group, contrary to what was observed in other grades. The EOR result can confirm the long-standing belief that there are no functional fields in the gadolinium-enhanced lesions of glioblastoma. Although there was no significance for OS, a divergence could be observed at the beginning of the Kaplan-Meier curves. Surprisingly, in glioblastoma, AC may have reduced early mortality by preventing an early postoperative decline in KPS (Fig. 1D, Table 3). The recent meta-analysis by Gerritsen et al. of AC for high-grade glioma also suggests the efficacy of AC and is in the process of being validated by RCTs in grade IV tumors.[16, 36, 38]

Effect of genetics and postoperative treatment

This study was not based on the WHO 2016 classification, as we could not analyze the 1p19q codeletion status in the early 2000s. In principle, we could have eliminated these cases, but since OS analysis was among the main purposes of the study, these cases and those with grades II-III require long follow-up. Recently, however, IDH status and 1p19q coding have been considered strict prognostic factors.[39, 40] The IDH status of 16 patients was unknown, but no significant difference was found between the AC and GA groups (p = 0.131). Most of the cases whose IDH status could not be identified were glioblastoma. At our facility, gene mutation search was not actively performed in the past for cases pathologically classified as glioblastoma. Approximately 90% of glioblastoma cases are IDH-wild type, in agreement with previous estimates.[40] In 26 cases, the 1p19q status could not be identified. However, since the percentage of 1p19q codeletion was not significantly different between the groups (p = 0.397), the effects of prognostic genetic factors are considered small, although we could not analyze O6-methylguanine (O6-MeG)-DNA methyltransferase promoter methylation status.

The inclusion of all gliomas in our analysis has an effect on post-treatment and may affect the analysis of prognosis. Our facility does not actively perform AC when we suspect glioblastoma. Indeed, glioblastoma is typically already symptomatic at the time of discovery and is often not indicated for AC, as shown in Table 1. Besides, it is not possible to accurately assess the WHO grade in the preoperative image. The reason for simultaneously analyzing tumors of different WHO grades was to reduce the selection bias. Furthermore, in the post-hoc analysis, no difference was noted after treatment between the AC group and the GA group, and the effect on prognosis was considered small.

Limitations

Our study is inherently limited by its retrospective design, leading to selection bias, lack of randomization, limited control of confounding factors, and difficulty in establishing causes and effects. Moreover, it did not adjust for eloquent area lesions when comparing the AC and GA groups. The selection of glioma patients should be limited to near eloquent lesions to investigate the effects of AC on EOR and OS, and previous studies have attempted to do so. Paradoxically, adjusting for eloquent lesions makes it difficult to adjust for KPS and age, which affects the OS; moreover, the small number of eloquent cases in the GA group leads to small sample size studies. There were 12/91 (13%) patients with near eloquent lesions in the GA group, although the analysis performed when excluding them did not change the results (data not shown). However, excluding the eloquent group from the GA group creates a bias for OS analysis. Besides, the cohort adjusted for eloquence is fundamentally enriched in perirolandic glioma cases, because eloquent glioma, which is an indication for GA, is abundant in the motor area and is considered less prevalent in the language-related area. Given that the most prominent feature of AC is preserving language function, this method is also limited. We believe that propensity score-matched analysis is the best adjustment for assessing EOR and OS in non-RCT studies.

Conclusions

Our extensive study quantitatively evaluated AC and GA removal rates and adjusted for bias with propensity score matching. If it is difficult to plan an RCT for patients with eloquent glioma, our propensity score-matched study provided retrospective evidence that AC can obtain EOR and OS equivalent to removing glioma under GA.

Declarations

Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflict of Interest: Not applicable.

Availability of data and material: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Authors' contributions: All authors contributed substantially to this work.

Ethics approval: This retrospective study was approved by the institutional review board of Tokyo Women’s Medical University.

Consent to participate: Not applicable.

Consent for publication: Not applicable.

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