Tortuosity of middle cerebral artery M1 segment and outcomes after mechanical thrombectomy

Abstract

Background

We aimed to quantify the tortuosity of the middle cerebral artery (MCA) and assess its effects on radiological and clinical outcomes in patients with acute MCA occlusions who received mechanical thrombectomy (MT).

Methods

This retrospective study enrolled 53 patients with acute ischemic stroke due to MCA M1 or M2 segment occlusion who underwent MT using stent retrievers (SRs). Tortuosity index (TI) was defined to quantify the tortuosity of the MCA M1 segment using the following formula: (actual distance / straight distance) × 100. For each patient, four TIs were measured in the anteroposterior and caudal views for both ipsilateral and contralateral sides to the occluded site (TI-APi, TI-APc, TI-CAUi, and TI-CAUc, respectively) using magnetic resonance angiography (MRA) or computed tomography angiography (CTA). We defined the first-pass effect (FPE) as first-pass mTICI classification ≥2b reperfusion.

Results

Patients who did not achieve FPE had significantly higher TI-APi (112 vs. 106; P = 0.004), TI-APc (111 vs. 105; P = 0.005), TI-CAUi (110 vs. 105; P = 0.002), and TI-CAUc (110 vs. 105; P = 0.001) than those who achieved FPE. In multivariable analysis, higher TI-APi, TI-CAUi, and TI-APc were independently associated with an increased rate of unsuccessful FPE (odds ratio (OR) [95% confidence interval (CI)]: 1.25 [1.02–1.61], 1.21 [1.01–1.45], and 1.27 [1.03–1.73], respectively). TI-CAUi, TI-APc, and TI-CAUc were also independent predictors of the occurrence of intracranial hemorrhage after MT (OR [95% CI]: 1.15 [1.01–1.38], 1.14 [1.01–1.38], 1.25 [1.02–1.52], respectively).

Conclusions

The TIs of the MCA M1 segment on both ipsilateral and contralateral sides were associated with unfavourable outcomes after MT.

Keywords

intracranial hemorrhages ischemic stroke middle cerebral artery prognosis thrombectomy

Introduction

After the success of multiple randomized clinical trials, mechanical thrombectomy (MT) has been established as a standard treatment for acute stroke secondary to large vessel occlusion.¹ Nevertheless, up to 15% of procedures still failed to recanalize sufficiently.^2–4 Additionally, MT may cause intracranial hemorrhage, which limits or even undoes its beneficial effects. Because the technical results of MT are directly related to neurological outcomes,⁵ it would be informative for clinical decision-making to identify preoperative risk factors that hinder the technical success.

The reperfusion failure can result from heterogenous causes, such as technical difficulties in reaching or passing the target occlusion, underlying nonembolic vessel diseases, thrombus composition, and spontaneous or iatrogenic reocclusion.⁶ Among the multifaceted factors, vascular anatomy should have a significant influence on the MT results. Critical vessel characteristics, including angulation and tortuosity, potentially affect the ability to advance MT devices toward the occlusion site as well as to effectively remove a thrombus.^6,7 Previous studies have addressed the unfavourable anatomy of the aortic arch or cervical carotid artery,^8–12 although the influence of intracranial vessel anatomy has been less studied. This may be partly due to the difficulty in assessing the vasculature of the intracranial artery, which is occluded and invisible on preoperative vessel imaging. In the present study, we defined the tortuosity index (TI) to quantify the tortuosity of the middle cerebral artery (MCA) M1 segment using postoperative vessel imaging and evaluated its prognostic implications after MT. We focused on the tortuosity of not only ipsilateral but also contralateral (i.e. non-occluded) sides of the MCA, which is measurable even before MT, ensuring its availability as a preoperative predictor.

Methods

Study design and participants

This study was conducted in accordance to the 1975 Declaration of Helsinki and ethical guidelines of our institution. The need for written informed consent was waived, owing to the retrospective design of the study. In this single-centre, retrospective, observational study, 118 patients with acute ischemic stroke due to large-vessel occlusion who underwent MT were assessed for eligibility between July 2015 and October 2020 (Figure 1). Among them, 67 patients had acute MCA occlusion on preoperative computed tomography angiography (CTA) and/or magnetic resonance angiography (MRA). We excluded seven patients with no retrievable thrombus in the diagnostic angiography at the time of MT, three patients who were not treated with stent retrievers (SRs) as a first-line strategy, two patients who could not gain access to the occluded site, and two with no radiological data available, leaving 53 patients with acute MCA M1 (n = 32) or M2 (n = 21) segment occlusions receiving MT using SRs for current analysis.

The baseline data collected for each patient included demographics, premorbid modified Rankin Scale (mRS) score, medical history, neurological and radiological findings, time from symptom onset to admission, procedure time, and concurrent use of intravenous alteplase. All strokes were diagnosed based on neurological observations, computed tomography (CT), and/or magnetic resonance imaging. Stroke severity was assessed using the National Institutes of Health Stroke Scale (NIHSS) (NIHSS). Etiologic subtypes of stroke were classified into cardioembolism, atherothrombotic, other causes, and undetermined causes using the Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria.¹³

Protocol for endovascular intervention

The indication for MT was determined according to the domestic guidelines published online by the Japanese Stroke Association, Japan Neurosurgical Society, and Japanese Society for Neuroendovascular Therapy (https://www.jstage.jstgo.jp/article/jstroke/42/4/42_10817/_pdf/-char/en). Non-enhanced CT images were first obtained, followed by 3-dimensional CTA. Ischemic lesions in the initial CT scans were rated on the basis of the Alberta Stroke Program Early Computed Tomography Score (ASPECTS).¹⁴ MT was performed by board-certified neurointerventionalists with any device approved by the Ministry of Health, Labor, and Welfare of Japan. In all cases, a 9-Fr balloon-guiding catheter was introduced to the cervical portion of the internal carotid artery. In our center, SR was selected as the first-line device, either with or without the combined use of an aspiration catheter. SRs used in this study included Solitaire (Medtronic, Irvine, CA), Trevo (Stryker, Kalamazoo, MI), Embotrap (Cerenovus, Irvine, CA), and Tron (Terumo, Gumma, Japan). Table 1 shows usage rates of each device by the date of study enrolment. When we used the aspiration catheters, the “aspiration catheter with proximal balloon (ASAP)” technique was primarily applied.^15,16 Namely, after the deployment of SR, a 5- to 7-Fr aspiration catheter was advanced up to the surface of the clot, to accomplish contact aspiration. The SR and microcatheter were withdrawn into the aspiration catheter, and subsequently the aspirator was withdrawn. Manual suction from the balloon-guiding catheter was simultaneously performed. The device selection and decision to switch to the second MT strategy were at the discretion of the operator.

Table 1.

Stent retrievers used for mechanical thrombectomy.

	All(n = 53)	Earlier inclusion(n = 26)	Later inclusion(n = 26)	P value
Solitaire	30 (56.6)	18 (69.2)	12 (44.4)	0.015
Trevo	14 (26.4)	8 (30.8)	6 (22.2)
Embotrap II	8 (15.1)	0	8 (29.6)
Tron	1 (1.9)	0	1 (3.7)

Figures are expressed as n (%).

Study participants were dichotomized into earlier (from July 2015 to August 2018; n = 26) and later (from September 2018 to October 2020; n = 27) inclusion groups by the date of study enrolment.

Definition of tortuosity index

The tortuosity of the MCA M1 segment was assessed by the time-of-flight MRA (n = 50) or 3-dimensional CTA (n = 3) conducted within one week after the MT. The MCA M1 segment was defined as the sphenoidal segment from the terminal bifurcation of the internal carotid artery up to the major (i.e. M1-M2) bifurcation or trifurcation.¹⁷ Early frontal or temporal branch was not regarded as the M1-M2 bifurcation. We defined the TI as the percent ratio of two distances in the following formula: (the actual distance of M1 segment / the theoretic shortest distance of M1 segment) × 100 (Figure 2).¹⁸ For example, a TI of 105 represents a 5% excess actual MCA M1 distance, compared to the theoretical optimal distance. The same definition has been applied to the cervical carotid and vertebral arteries in previous studies.^8,12,19 Angiographic images were reviewed by a blinded observer (T.H.). The distances were measured in millimetres up to two decimal places, using the centre of the vessel as the central axis. Each patient had four TI measurements in the anteroposterior and caudal views for both ipsilateral and contralateral sides of the vessel occlusion (TI-APi, TI-APc, TI-CAUi, and TI-CAUc, respectively).

Outcome evaluations

Angiographic outcomes were assessed by modified Thrombolysis in Cerebral Infarction (mTICI) classification on the last angiogram.¹⁷ We defined the first-pass effect (FPE) as having achieved mTICI grade ≥2b reperfusion after a single attempt with MT. Intracerebral hemorrhage was defined according to the European Cooperative Acute Stroke Study (ECASS) II criteria.²⁰ Functional outcomes were measured by mRS at three months after the index stroke.

Statistical analysis

Categorical variables are expressed as numbers (percentages). Quantitative variables with normal distribution are expressed as mean (standard deviation), while those with non-normal distribution are expressed as median (interquartile range). Baseline and outcome variables were compared between the patients who achieved FPE and those who did not. Intergroup differences were assessed using the χ² test for categorical variables and Student's t-test or Mann–Whitney U test for quantitative variables. The Pearson's correlation coefficient (r) was used to measure the strength of the linear association between the different TIs. To assess the effects of TIs on outcomes, we performed multiple logistic regression analysis that was adjusted for age, sex, tissue plasminogen activator use, procedure (stent retriever or combined), and variables with P-values of <0.1 in the univariate analysis (NIHSS, affected side, ASPECTS, puncture-to-recanalization time). Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. We established the cutoff values of each TI based on the receiver operating characteristic curves. The area under the curve, also referred to as the C-statistic, represents the ability of the index to predict the outcomes. In all analyses, a P-value <0.05 was considered significant.

Results

Among the 53 patients (mean age, 73.4 years; male, 54.7%) included in this study, 14, 18, and 21 had occlusions in the M1 proximal, M1 distal, and M2 segments, respectively. Twenty-two patients (41.5%) achieved the FPE (first-pass mTICI ≥2b reperfusion). Table 2 shows baseline characteristics of patients with and without FPE. There were no differences in the demographics or medical histories between the two groups, whereas the four TIs were significantly higher in patients who did not achieve FPE. As shown in Table 3, those in the non-FPE group were more likely to have a higher NIHSS score at baseline, left-sided stroke, lower ASPECTS, and longer time from puncture to recanalization. The rate of combined use of aspiration catheter was similar between patients with and without FPE (50.0% 48.4%; P = 0.91). Figure 3 shows the correlations of the TIs according to the side and direction. There was a moderately positive linear relationship between ipsilateral and contralateral TIs in both anteroposterior and caudal views.

Table 2.

Baseline characteristics.

	All (n = 53)	1 pass mTICI ≥2b		P value
	All (n = 53)	Yes (n = 22)	No (n = 31)	P value
Age, y, mean (SD)	73.4 (9.6)	73.0 (8.7)	73.7 (10.2)	0.78
Male, n (%)	29 (54.7)	11 (50.0)	18 (58.1)	0.56
Premorbid mRS, n (%)				0.62
0	45 (84.9)	20 (90.9)	25 (80.7)
1	4 (7.5)	1 (4.6)	3 (9.7)
2	3 (5.7)	1 (4.6)	2 (6.5)
3	1 (1.9)	0	1 (3.2)
Medical history, n (%)
Hypertension	27 (50.9)	12 (54.6)	15 (48.4)	0.66
Diabetes mellitus	9 (17.0)	4 (18.2)	5 (16.1)	0.84
Dyslipidemia	15 (28.3)	4 (18.2)	11 (35.5)	0.16
Atrial fibrillation	27 (50.9)	12 (54.6)	15 (48.4)	0.66
Chronic kidney disease	11 (20.8)	6 (27.3)	5 (16.1)	0.33
Current smoking	8 (15.1)	5 (22.7)	3 (9.7)	0.19
Stroke	5 (9.4)	1 (4.6)	4 (12.9)	0.29
Coronary artery disease	7 (13.2)	2 (9.1)	5 (16.1)	0.45
Tortuosity index
TI-APi	109 (8)	106 (5)	112 (8)	0.004
TI-APc	108 (8)	105 (5)	111 (8)	0.005
TI-CAUi	108 (6)	105 (5)	110 (6)	0.002
TI-CAUc	108 (6)	105 (4)	110 (6)	0.001

mRS, modified Rankin Scale; mTICI, modified thrombolysis in cerebral ischemia; SD, standard deviation.

TI-APi and TI-APc indicate the tortuosity indices of the ipsilateral and contralateral sides of the occlusion in the anteroposterior view, respectively.

TI-CAUi and TI-CAUc indicate the tortuosity indices of the ipsilateral and contralateral sides of the occlusion in the caudal view, respectively.

Table 3.

Information on index stroke and treatments.

	All (n = 53)	1 pass mTICI ≥2b		P value
	All (n = 53)	Yes (n = 22)	No (n = 31)	P value
Index stroke
Onset unknown, n (%)	18 (34.0)	9 (40.9)	9 (29.0)	0.37
NIHSS, median (IQR)	17 (10.5–23)	14 (8–20)	18 (13–24)	0.042
Occlusion site, n (%)				0.87
M1 proximal segment	14 (26.4)	5 (22.7)	9 (29.0)
M1 distal segment	18 (34.0)	8 (36.4)	10 (32.3)
M2 segment	21 (39.6)	9 (40.9)	12 (38.7)
Affected side, left, n (%)	31 (58.5)	5 (22.7)	17 (54.8)	0.017
ASPECTS, median (IQR)	9 (6.5–10)	10 (8.75–10)	9 (6–9)	0.003
TOAST classification, n (%)				0.95
Cardioembolism	30 (56.6)	13 (59.1)	17 (54.8)
Atherothrombotic	8 (15.1)	3 (13.6)	5 (16.1)
Others	4 (7.5)	2 (9.1)	2 (6.5)
Undetermined	11 (20.8)	4 (18.2)	7 (22.6)
Treatment
IV t-PA use, n (%)	27 (50.9)	12 (54.6)	15 (48.4)	0.66
Time course, min, mean (SD)
Door to picture	15 (7)	14 (6)	15 (7)	0.49
Door to puncture	73 (38)	71 (33)	75 (42)	0.75
Door to recanalization	108 (42)	105 (34)	111 (48)	0.57
Puncture to IFR	36 (18)	33 (15)	37 (21)	0.43
Puncture to recanalization	63 (35)	45 (15)	75 (39)	0.017
Procedure, n (%)				0.91
Stent retriever	27 (50.9)	11 (50.0)	16 (51.6)
Combined	26 (49.1)	11 (50.0)	15 (48.4)

ASPECT, Alberta Stroke Program Early Computed Tomography score; IFR, immediate flow restoration; IQR, interquartile range; IV-tPA, intravenous tissue plasminogen activator; mRS, modified Rankin Scale; mTICI, modified thrombolysis in cerebral ischemia; NIHSS, National Institutes of Health Stroke Scale; SD, standard deviation; TOAST, Trial of Org 10172 in Acute Stroke Treatment.

Table 4 shows the associations of TIs with angiographic outcomes, occurrence of intracranial hemorrhage, and three-month functional prognosis. Higher TI-APc was significantly associated with the longer time from puncture to recanalization. TIs were generally higher in patients with poor angiographic and clinical outcomes than those with favourable outcomes by significant differences. Results of multivariable analysis are presented in Table 5. In the fully-adjusted models, higher TI-APi, TI-APc, and TI-CAUi were independently associated with an increased rate of unsuccessful FPE (OR [95% CI], 1.25 [1.02–1.61]; 1.21 [1.01–1.45]; and 1.27 [1.03–1.73], respectively). The optimal threshold values of TI-APi, TI-APc, and TI-CAUi for unsuccessful FPE calculated using receiver operating characteristic curves were 108 (C-statistic, 0.787), 107 (C-statistic, 0.746), and 108 (C-statistic, 0.770), respectively. In addition, TI-APc, TI-CAUi, and TI-CAUc were independent predictors of any intracranial hemorrhage (OR [95% CI], 1.15 [1.01–1.38]; 1.14 [1.01–1.38]; and 1.25 [1.02–1.52], respectively). The optimal threshold values of TI-APc, TI-CAUi, and TI-CAUc for intracranial hemorrhages were 107 (C-statistic, 0.726), 110 (C-statistic, 0.787), and 109 (C-statistic, 0.819), respectively.

Table 4.

Tortuosity index and outcomes.

	TI-APi	TI-APc	TI-CAUi	TI-CAUc
Angiographic outcome
Puncture to recanalization time <30 min
Yes (n = 19)	109 (8)	105 (4)	108 (8)	107 (4)
No (n = 34)	111 (7)	109 (6)*	111 (8)	108 (6)
mTICI ≥2b
Yes (n = 43)	108 (8)	106 (6)	107 (6)	105 (5)
No (n = 10)	115 (4)*	117 (9)**	112 (5)*	111 (8)**
1 pass mTICI ≥2b
Yes (n = 22)	106 (5)	107 (5)	105 (5)	105 (4)
No (n = 31)	112 (8)**	113 (6)**	110 (6)**	110 (6)**
mTICI 3
Yes (n = 17)	110 (9)	107 (7)	108 (7)	107 (6)
No (n = 36)	109 (7)	109 (8)	108 (5)	109 (6)
1 pass mTICI 3
Yes (n = 11)	107 (7)	106 (7)	106 (6)	105 (3)
No (n = 42)	110 (8)	109 (8)	109 (6)	109 (6)*
Hemorrhagic complication
Parenchymal hematoma
No (n = 45)	109 (8)	107 (6)	108 (6)	108 (6)
Yes (n = 8)	113 (6)	115 (12)*	110 (6)	111 (4)
Subarachnoid hemorrhage
No (n = 42)	107 (5)	106 (5)	107 (6)	106 (4)
Yes (n = 11)	117 (11)**	115 (6)**	114 (10)**	115 (6)**
Any intracranial hemorrhage
No (n = 37)	108 (6)	107 (5)	106 (4)	106 (4)
Yes (n = 16)	114 (10)**	113 (9)**	112 (7)**	113 (7)**
Functional outcome
mRS <3 at 3 months
Yes (n = 27)	106 (5)	107 (6)	105 (4)	106 (4)
No (n = 26)	113 (9)**	110 (9)	111 (6)**	110 (6)*
mRS <2 at 3 months
Yes (n = 22)	105 (3)	106 (6)	106 (4)	106 (5)
No (n = 31)	112 (9)**	110 (9)	110 (7)*	109 (6)

Shown are mean (standard deviation) of tortuosity index.

mRS, modified Rankin Scale; mTICI, modified Thrombolysis in Cerebral Ischemia.

TI-APi and TI-APc indicate the tortuosity indices of the ipsilateral and contralateral sides of the occlusion in the anteroposterior view, respectively.

TI-CAUi and TI-CAUc indicate the tortuosity indices of the ipsilateral and contralateral sides of the occlusion in the caudal view, respectively.

* P < 0.05 by unpaired t test.

** P < 0.01 by unpaired t test.

Table 5.

Multivariable analysis.

	Age- and sex-adjusted OR (95% CI)	P value	Fully-adjusted OR (95% CI)*	P value*
TI-APi
Unsuccessful 1 pass mTICI ≥2b	1.23 (1.07–1.46)	0.008	1.25 (1.02–1.61)	0.033
Any ICH	1.13 (1.01–1.26)	0.028	1.12 (0.90–1.39)	0.25
mRS ≥3 at 3 months	1.22 (1.07–1.46)	0.001	1.07 (0.82–1.42)	0.61
TI-APc
Unsuccessful 1 pass mTICI ≥2b	1.16 (1.04–1.34)	0.019	1.21 (1.01–1.45)	0.046
Any ICH	1.07 (0.99–1.16)	0.10	1.15 (1.01–1.38)	0.049
mRS ≥3 at 3 months	1.09 (0.99–1.22)	0.11	1.08 (0.87–1.40)	0.51
TI-CAUi
Unsuccessful 1 pass mTICI ≥2b	1.26 (1.09–1.53)	0.006	1.27 (1.03–1.73)	0.024
Any ICH	1.12 (1.01–1.28)	0.046	1.14 (1.01–1.38)	0.049
mRS ≥3 at 3 months	1.22 (1.07–1.46)	0.001	1.03 (0.80–1.33)	0.80
TI-CAUc
Unsuccessful 1 pass mTICI ≥2b	1.29 (1.11–1.59)	0.005	1.22 (0.99–1.58)	0.057
Any ICH	1.16 (1.04–1.33)	0.018	1.25 (1.02–1.52)	0.011
mRS ≥3 at 3 months	1.16 (1.02–1.36)	0.045	1.07 (0.85–1.37)	0.55

CI, confidence interval; ICH, intracranial hemorrhage; mRS, modified Rankin Scale; mTICI, modified thrombolysis in cerebral ischemia; OR, odds ratio.

TI-APi and TI-APc indicate the tortuosity indices of the ipsilateral and contralateral sides of the occlusion in the anteroposterior view, respectively.

TI-CAUi and TI-CAUc indicate the tortuosity indices of the ipsilateral and contralateral sides of the occlusion in the caudal view, respectively.

* Adjusted for age, sex, initial National Institutes of Health Stroke Scale score, affected side (left or right), Alberta Stroke Program Early Computed Tomography score, tissue plasminogen activator use, door-to-puncture time, puncture-to-recanalization time, procedure (stent retriever or combined).

Discussion

In this retrospective observational study conducted on patients with acute MCA occlusion receiving MT with SRs, the tortuosity of the MCA M1 segment defined by TI was associated with unfavourable outcomes after MT. The TI value on the ipsilateral side to the occluded site indicated a positive correlation with that on the contralateral side in both anteroposterior and caudal views. More importantly, the contralateral TI had a predictive value similar to that of the ipsilateral TI. Preoperative CTA or MRA analysis can rapidly identify the vasculature of the contralateral side, allowing the use of contralateral TI as a preoperative predictor, whereas ipsilateral TI is usually unmeasurable due to the occlusion. In our estimate, an approximately 8% excess elongation of the M1 segment compared to the straight distance showed the best predictive performance. Some methodological modifications may be possible for more accurate assessment of arterial tortuosity by taking into account the number and degree of angulation or 3D vasculature.¹⁸ However, we primarily focused on the simplicity of index that can be applicable to the acute stroke care setting where the time saving is a major concern. Therefore, TI can serve as a useful parameter for interventionalists to guide them in planning optimal devices, techniques, or management strategies in a timely manner.

TI has been shown to be a reproducible method for quantifying arterial tortuosity¹⁸ and has been used in various vascular systems, including the aorta, carotid, femoral, and vertebral arteries.^8,12,19,21 For patients with acute ischemic stroke receiving MT, Gomez-Paz et al. first reported that a TI of the cervical internal carotid artery >110 was associated with an extended MT procedural time.¹² However, the TI has not been applied to intracranial arteries in this population, whereas several studies examined the degree of curve angle of the M1 segment instead.^22–24 Schwaiger et al. measured the angles between the terminal internal carotid artery and the most downward M1 segment and between the most proximal M1 and the M1 segment immediately conterminous to the proximal thrombus face, and showed that MT using SR was significantly less effective in patients with large vessel angles.²² Similarly, Bernava et al. measured the angle of interaction formed between the aspiration catheter and the clot in patients treated with contact aspiration.²³ The study found that the angle of >125.5° significantly influenced the MT outcomes. The curve angle of M1 segment was also predictive of recanalization failure in patients treated with the Merci retrieval system.²⁴ As such, it is likely that the curved M1 segment is an important outcome determinant after MT using any device. Our findings build on the prior research by demonstrating the utility of not the angle but the distance factor (i.e. TI) for intracranial arteries as a marker of adverse outcomes after MT.

Tortuous intracranial arteries may affect the mechanics of SR.^7,22 In strongly curved segments, the SR can be stretched during the retrieval process, which causes a lower wall apposition and constriction of the stent cell size. This potentially reduces the interaction force between the SR and clot, and consequently fails to catch the thrombus. Unsuccessful reperfusion during the first pass leads to multiple device passes and prolongation of procedure time, potentially reducing the clinical efficacy while increasing the bleeding risk.⁵ Experimental models observed different performances between SR devices in tortuous arteries.²⁵ Namely, some SRs were elongated and collapsed in curved segments, resulting in the dislodgement of clot, but other SRs were not. Such data can provide clues for choosing optimal SR devices for treating patients with a higher TI.

Limitations

Our study had several limitations. First, it was a single-centre retrospective study with a relatively small sample size. The MT procedures were not performed by the same operator, and the devices and techniques used for each patient were selected at the discretion of the attending operators. Therefore, the generalizability of our findings is limited. Second, TI was determined using 2-dimensional images, although 3-dimensional evaluation is necessary for measuring precise vascular length. However, the acquisition and analysis of 3-dimensional data are time-consuming and were not considered feasible in an acute setting. The primary purpose of this study was to assess the performance of a simple parameter obtained using routine software. Third, data on inter-rater reproducibility for TI measurements were not available in our study. Finally, even after multivariable adjustments, residual confounding factors cannot be ruled out. In particular, several unfavourable anatomical features of the aortic arch and cervical arteries could be major obstacles during MT. A more extensive model of analysis is warranted to comprehensively assess the prognostic impact of the vascular anatomy.

Conclusions

TI, an easily measurable parameter of MCA M1 segment tortuosity, is an important non-modifiable risk factor for predicting an unsuccessful early recanalization as well as the occurrence of intracranial hemorrhage after MT. The TI of the contralateral side to the occlusion was proportional to that of the ipsilateral side and was predictive of poor outcomes, suggesting the utility of contralateral TI in preoperative decision making.

Footnotes

Authors’ contribution:

Conception and design: TH, ShiS. Acquisition of data: TH, ShiS, KK, YT, TM, ToI, ShoS, BR, TaI. Statistical analysis and data interpretation: TH, ShiS. Drafting the article: TH. Critically revising the article: all authors. Study supervision: YO, YN.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Takao Hoshino

Shinsuke Sato

Shogo Shima

Yasunari Niimi

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