Cerebral Bypass Surgery: Level of Evidence and Grade of Recommendation

Flow capacity of a superficial temporal artery as a donor in a consecutive series of 100 patients with superficial temporal artery-middle cerebral artery bypass

OBJECTIVE

A superficial temporal artery-middle cerebral artery (STA-MCA) bypass is classically considered a low-flow bypass. It is known that the flow in the flow augmentation STA-MCA bypass is influenced by flow demand of the revascularized territory and can reach significantly higher values. The authors report their intraoperative flow measurement data in a consecutive series of 100 STA-MCA bypasses performed at their institution. Moreover, in a subanalysis, they show the postoperative bypass flow measured with quantitative MR angiography (qMRA) noninvasive optimal vessel analysis (NOVA).

METHODS

Between January 2013 and October 2023, 100 patients with acute, subacute, or chronic large-vessel occlusion (LVO) or moyamoya disease underwent a flow augmentation STA-MCA bypass revascularization at the authors' department with intraoperative bypass flow measurement. Patients with atherosclerotic LVO who underwent bypass surgery within a 6-week period following the onset of ischemic stroke symptoms were categorized into the acute bypass group, encompassing both acute and subacute LVO cases. Conversely, those who underwent bypass surgery > 6 weeks after the last occurrence of ischemic stroke were classified as the chronic group. Since May 2019, a consecutive subgroup of 37 patients received a postoperative (before discharge) bypass flow measurement with the qMRA-NOVA imaging tool.

RESULTS

The mean ± SD intraoperative bypass flow in this consecutive series of 100 STA-MCA bypasses was 53.5 ± 28.8 ml/min (range 14-145 ml/min). In the subanalysis, there was no difference in the intraoperative flow capacity between the acute and chronic groups and between the moyamoya and acute groups. Patients in the moyamoya group showed a significantly higher flow rate in the STA-MCA bypass compared with the chronic group (63.0 ± 30.2 ml/min vs 48.4 ± 26.5 ml/min, p = 0.03). In a consecutive subanalysis of 37 STA-MCA bypass cases, postoperative flow measurements were also performed using qMRA-NOVA, showing a significant increase in the flow of STA-MCA bypasses after surgery compared with intraoperative flow measurements (mean intraoperative bypass flow rate vs qMRA-NOVA postoperative bypass flow rate: 73.4 ± 29.9 ml/min vs 111.3 ± 51.4 ml/min, p = 0.005).

CONCLUSIONS

Using intraoperative and postoperative quantitative flow measurements of the STA, the data confirm that the flow in the flow augmentation STA-MCA bypass is influenced by the flow demand of the revascularized territory and can reach high values if needed. Moreover, the significant flow increase in the postoperative flow measurement using qMRA-NOVA demonstrates that the bypass can increase its flow over time.

Current Indications, Trends, and Long-Term Results of 233 Bypasses to Treat Complex Intracranial Aneurysms: A Location-Specific Analysis

BACKGROUND AND OBJECTIVES

Advances in endovascular flow diverters have led to a secular shift in the management of brain aneurysms, causing debate on current bypass indications. We therefore sought to investigate the long-term results, current indications, and trends of bypasses for brain aneurysms.

METHODS

We retrospectively reviewed bypasses performed between 2005 and 2022 to treat brain aneurysms. Demographic, clinical, and radiological data were collected till the most recent follow-up. Aneurysm occlusion and graft patency was noted on cerebral angiogram in the immediate postoperative, 3-month, and most recent follow-up periods. Clinical outcomes (modified Rankin scores) and complications were assessed at 3 month and most recent follow-up. Trends in bypass volume and graft patency were assessed in 5-year epochs. Results were dichotomized based on aneurysm location to generate location-specific results and trends.

RESULTS

Overall, 203 patients (mean age 50 years, 57% female patients) with 207 cerebral aneurysms were treated with 233 cerebral bypasses with a mean follow-up of 2 years. Fusiform morphology was the most common bypass indication. Aneurysm occlusion on immediate postoperative and final follow-up angiogram was 89% (184/207) and 96% (198/207), respectively. Graft patency rate in the immediate postoperative period and most recent follow-up was 95% (222/233) and 92% (215/233), respectively. Of 207 aneurysms, 5 (2%) recurred. Of 203 patients, 81% (165) patients had modified Rankin scores of 0-2 at the 3-month follow-up and 11 patients died (mortality 5%). Although there was a steady decrease in the bypass volume over the study period, the proportion of bypasses for recurrent aneurysms increased serially. Posterior circulation aneurysms had lower rates of aneurysm occlusion and significantly higher incidence of postoperative strokes and deaths ( P = .0035), with basilar artery aneurysms having the worst outcomes.

CONCLUSION

Bypass indications have evolved with the inception of novel flow diverters. However, they remain relevant in the cerebrovascular surgeon's armamentarium, and long-term results are excellent.

BOLD Cerebrovascular Reactivity and NOVA Quantitative MR Angiography in Adult Patients with Moyamoya Vasculopathy Undergoing Cerebral Bypass Surgery

Revascularization surgery for the symptomatic hemisphere with hemodynamic impairment is effective for Moyamoya vasculopathy patients. However, careful patient selection is crucial and ideally supported by advanced quantitative hemodynamic imaging. Recently, blood oxygenation level-dependent cerebrovascular reactivity (BOLD-CVR) and quantitative magnetic resonance angiography with non-invasive optimal vessel analysis (qMRA-NOVA) have gained prominence in assessing these patients. This study aims to present the results of BOLD-CVR and qMRA-NOVA imaging along with the changes in cerebral hemodynamics and flow status following flow augmentation with superficial temporal artery-middle cerebral artery (STA-MCA) bypass in our Moyamoya vasculopathy patient cohort. Symptomatic patients with Moyamoya vasculopathy treated at the Clinical Neuroscience Center of the University Hospital Zurich who underwent hemodynamic and flow imaging (BOLD-CVR and qMRA-NOVA) before and after bypass were included in the analysis. Reduced hemispheric volume flow rates, as well as impaired BOLD-CVR, were measured in all 12 patients with Moyamoya vasculopathy before STA-MCA bypass surgery. Following the surgical procedure, post-operative BOLD-CVR demonstrated a non-significant increase in BOLD-CVR values within the revascularized, symptomatic middle cerebral artery territory and cerebral hemisphere. The results of the statistical tests should be viewed as indicative due to the small sample size. Additionally, post-operative qMRA-NOVA revealed a significant improvement in the hemispheric volume flow rate of the affected hemisphere due to the additional bypass flow rate. Our findings affirm the presence of hemodynamic and flow impairments in the symptomatic hemisphere of the Moyamoya vasculopathy patients. Bypass surgery proves effective in improving both BOLD-CVR impairment and the hemispheric volume flow rate in our patient cohort.

Association of Bypass Surgery and Mortality in Moyamoya Disease

BACKGROUND

Patients with moyamoya disease (MMD) have a high risk of stroke or death. We investigated whether extracranial to intracranial bypass surgery can reduce mortality by preventing strokes in patients with MMD.

METHODS AND RESULTS

This nationwide retrospective cohort study encompassed patients with MMD registered under the Rare Intractable Diseases program via the Relieved Co-Payment Policy between 2006 and 2019, using the Korean National Health Insurance Service database. Following a 4-year washout period, landmark analyses were employed to assess mortality and stroke occurrence between the bypass surgery group and the nonsurgical control group at specific time points postindex date (1 month and 3, 6, 12, and 36 months). The study included 18 480 patients with MMD (mean age, 40.7 years; male to female ratio, 1:1.86) with a median follow-up of 5.6 years (interquartile range, 2.5-9.3; mean, 6.1 years [SD, 4.0 years]). During 111 775 person-years of follow-up, 265 patients in the bypass surgery group and 1144 patients in the nonsurgical control group died (incidence mortality rate of 618.1 events versus 1660.3 events, respectively, per 105 person-years). The overall adjusted hazard ratio (HR) revealed significantly lower all-cause mortality in the bypass surgery group from the 36-month landmark time point, for any stroke mortality from 3- and 6-month landmark time points, and for hemorrhagic stroke mortality from the 6-month landmark time point. Furthermore, the overall adjusted HRs for hemorrhagic stroke occurrence were beneficially maintained from all 5 landmark time points in the bypass surgery group.

CONCLUSIONS

Bypass surgery in patients with MMD was associated with a lower risk of all-cause and hemorrhagic stroke mortality and hemorrhagic stroke occurrence compared with nonsurgical control.

Screening of postoperative cerebral hyperperfusion syndrome in moyamoya disease: a three-dimensional pulsed arterial-spin labeling magnetic resonance imaging approach

Introduction

Moyamoya disease (MMD) is associated with a risk of postoperative cerebral hyperperfusion syndrome (CHS) after revascularization surgery. This study aimed to explore the feasibility of using three-dimensional pulsed arterial spin labeling (3D PASL) and phase contrast (PC) magnetic resonance imaging (MRI) for predicting CHS occurrence in patients with MMD before revascularization surgery.

Methods

Overall, 191 adult patients (207 hemispheres) with MMD who underwent combined revascularization surgery were included in this study. Preoperative 3D PASL-MRI and PC-MRI were performed before surgery. The PASL-MRI data were analyzed using SPM12. Patient clinical information, average flow, and preoperative cerebral blood flow (CBF) were compared between the non-CHS and CHS groups.

Results

Among the patients, 45 (21.74%) developed CHS after revascularization surgery. No significant differences were noted in age, sex, clinical symptoms, hypertension, diabetes, surgical side, or history of revascularization surgery between the non-CHS and CHS groups. However, the average flow in the superficial temporal artery was significantly lower in the CHS group than in the non-CHS group (p < 0.05). Furthermore, 11 clusters of preoperative CBF values were significantly greater in the CHS group than in the non-CHS group [p < 0.05, false discovery rate (FDR) corrected]. A significant correlation was also observed between the preoperative time-to-flight MR angiography (MRA) scores and CBF values in patients with MMD (p < 0.05).

Conclusion

Compare patients with lower preoperative CBF and higher preoperative average flow in the STA, patients with higher preoperative CBF and lower preoperative average flow in the STA are more likely to develop postoperative CHS Preoperative PASL-MRI and PC-MRI examinations may help to screen patients at high risk of developing CHS after revascularization surgery.

Hemodynamics of vascular shunts: trends, challenges, and prospects

Vascular bypass surgery takes a significant place in the treatment of vascular disease. According to various assessments, this type of surgery is associated with almost 20 % of all vascular surgery episodes (up to 23 % according to the Federal Neurosurgical Center of Novosibirsk). Even though the problem of using of vascular grafts is obvious and natural, many problems associated with them are not still elucidated. From the mechanics' point of view, a vascular bypass is a converging or diverging tee, and the functioning of such structures still does not have strict mathematical formulations and proofs in the general case, which forces many researchers to solve specific engineering problems associated with shunting. Mathematical modeling, which is the gold standard for virtual simulations of industrial and medical problems, faces great difficulties and limitations in solving problems for vascular bypasses. Complications in the treatment of the vascular disease may follow the difficulties in mathematical modeling, and the price can be a cardiac arrest or a stroke. This work is devoted to the main aspects of the medical application of vascular bypasses and their functioning as a mechanical system, as well the mathematical aspects of their possible setup.

Flow augmentation STA-MCA bypass evaluation for patients with acute stroke and unilateral large vessel occlusion: a proposal for an urgent bypass flowchart

OBJECTIVE

Endovascular recanalization trials have shown a positive impact on the preservation of ischemic penumbra in patients with acute large vessel occlusion (LVO). The concept of penumbra salvation can be extended to surgical revascularization with bypass in highly selected patients. For selecting these patients, the authors propose a flowchart based on multimodal MRI.

METHODS

All patients with acute stroke and persisting internal carotid artery (ICA) or M1 occlusion after intravenous lysis or mechanical thrombectomy undergo advanced neuroimaging in a time window of 72 hours after stroke onset including perfusion MRI, blood oxygenation level-dependent functional MRI to evaluate cerebrovascular reactivity (BOLD-CVR), and noninvasive optimal vessel analysis (NOVA) quantitative MRA to assess collateral circulation.

RESULTS

Symptomatic patients exhibiting persistent hemodynamic impairment and insufficient collateral circulation could benefit from bypass surgery. According to the flowchart, a bypass is considered for patients 1) with low or moderate neurological impairment (National Institutes of Health Stroke Scale score 1-15, modified Rankin Scale score ≤ 3), 2) without large or malignant stroke, 3) without intracranial hemorrhage, 4) with MR perfusion/diffusion mismatch > 120%, 5) with paradoxical BOLD-CVR in the occluded vascular territory, and 6) with insufficient collateral circulation.

CONCLUSIONS

The proposed flowchart is based on the patient's clinical condition and multimodal MR neuroimaging and aims to select patients with acute stroke due to LVO and persistent inadequate collateral flow, who could benefit from urgent bypass.

Neuroendocrine Carcinoma at the Sphenoid Sinus Misdiagnosed as an Olfactory Neuroblastoma and Resected Using High-Flow Bypass

In the diagnosis of olfactory neuroblastoma (ONB), the presence of S-100–positive sustentacular cells surrounding the tumor is important; however, these are also present in normal nasal sinus epithelium. Although ONB often has a different final diagnosis, complete resection of the tumor has a good prognosis and minimally affects the patient’s treatment plan. When the tumor extends around the internal carotid artery (ICA), complete resection is difficult due to the high risk of vascular injury; revascularization using high-flow bypass can avoid this complication. In the present case, the tumor was located in the left sphenoid sinus and extended around the ICA. Preoperative biopsy tissue was positive for neuroendocrine markers and slightly positive for S-100 protein, leading to a diagnosis of ectopic ONB. High-flow bypass revascularization with trapping of the ICA allowed complete tumor resection. The postoperative histopathological diagnosis was neuroendocrine carcinoma, showing no S-100 protein-positive cells. There was no sign of recurrence at 30 months after surgery without additional treatment. This case demonstrates that the presence of S-100 protein-positive cells in ONB may be misleading. Although misdiagnosis of ectopic ONB should be anticipated, a complete resection of the tumor is an effective treatment strategy.

Preoperative Collateral Perfusion Using Arterial Spin Labeling: A Predictor of Surgical Collaterals in Moyamoya Angiopathy

Objectives

Various degrees of surgical collateral circulation are often found in moyamoya angiopathy (MMA) patients after revascularization. Little is known about arterial spin labeling (ASL) that affects surgical collateral circulation. This study aimed to investigate the effect of ASL on surgical collaterals in patients with MMA after combined bypass surgery.

Methods

MMA patients with complete radiological and clinical information, who had undergone combined bypass, were enrolled in this study. Surgical collaterals were classified as good or poor based on the Matsushima standard. Cerebral perfusion on ASL was quantitatively analyzed as relative cerebral blood flow (rCBF). The qualitative collateral score was calculated using a four-grade scale. Univariable and multivariable logistic regressions were performed to identify the predictors for surgical collaterals after combined bypass.

Results

In total, 66 hemispheres of 61 patients (47 years old ± 8.66) were prospectively included (29 and 37 hemispheres with good and poor surgical collaterals, respectively). The presurgical collateral score was significantly lower in patients with good surgical collaterals (13.72 scores ± 7.83) than in those with poor surgical collaterals (19.16 scores ± 6.65, P = 0.005). The presurgical rCBF and modified Rankin scale (mRS) scores were not significantly different between the two groups (P_rCBF = 0.639, P_mRS = 0.590). The collateral score was significantly elevated (good: 13.72 scores ± 7.83 vs. 20.79 scores ± 6.65, P < 0.001; poor: 19.16 scores ± 6.65 vs. 22.84 scores ± 5.06, P < 0.001), and the mRS was reduced (good: 1.66 scores ± 1.14 vs. 0.52 scores ± 0.83, P < 0.001; poor: 1.49 scores ± 0.90 vs. 0.62 scores ± 0.76, P < 0.001) in patients after revascularization. Multivariable logistic regression showed that preoperative collateral scores [odds ratio (OR): 0.791; 95% confidence interval (CI): 0.695, 0.900; P < 0.001], age (OR: 0.181; 95% CI: 0.039, 0.854; P = 0.031), sex (OR: 0.154; 95% CI: 0.035, 0.676; P = 0.013), and hypertension (OR: 0.167; 95% CI: 0.038, 0.736; P = 0.018) were predictors of surgical collaterals after combined revascularization.

Conclusion

The preoperative collateral score based on ASL could be a predictor for surgical collaterals in patients with MMA after combined bypass surgery. Combined with age, sex, and hypertension, it may have a better predictive effect.

Trends in Literature on Cerebral Bypass Surgery: A Systematic Review

INTRODUCTION

Ever since the beginning of cerebral bypass surgery, the role of the bypass has been debated and indications have changed over the last 5 decades. This systematic literature research analysed all clinical studies on cerebral bypass that have been published from January 1959 to January 2020 for their year of publication, country of origin, citation index, role of and indication for bypass, bypass technique, revascularized territory, flow capacity, and title (for word cloud analysis per decade).

METHODS

A systematic literature research was conducted using PubMed, Web of Science, EMBASE, and SCOPUS databases. All studies that have been published until January 1, 2020, were included.

RESULTS

Of 6,013 identified studies, 2,585 were included in the analysis. Of these, n = 1,734 (67%) studies addressed flow-augmentation bypass and n = 701 (27%) addressed flow-preservation bypass. The most common indication reported for flow augmentation is moyamoya (n = 877, 51%), followed by atherosclerotic steno-occlusive disease (n = 753, 43%). For flow preservation, the most common indication is studies reporting on cerebral aneurysm surgery (n = 659, 94%). The increasing popularity of reporting on these bypass operations almost came to an end with the FDA approval of flow diverters for aneurysm treatment in 2011. Japan is the country with the most bypass studies (cumulatively published 933 articles), followed by the USA (630 articles) and China (232 articles).

DISCUSSION/CONCLUSION

Clinical studies on cerebral bypass surgery have become increasingly popular in the past decades. Since the introduction of moyamoya as a distinct pathologic entity, Asian countries in particular have a very active community regarding this disease, with an increasing number of articles published every year. Studies on bypass for chronic steno-occlusive disease peaked in the 1980s but have remained the main focus of bypass research, particularly in many European departments. The number of reports published on these bypass operations significantly decreased after the FDA approval of flow diverters for aneurysm treatment in 2011.

Controversies and Advances in Adult Intracranial Bypass Surgery in 2020

Cerebral revascularization utilizing a variety of bypass techniques can provide either flow augmentation or flow replacement in the treatment of a range of intracranial pathologies, including moyamoya disease, intracranial atherosclerotic disease, and complex aneurysms that are not amenable to endovascular or simple surgical techniques. Though once routine, the publication of high-quality prospective evidence, along with the development of flow-diverting stents, has limited the indications for extracranial-to-intracranial (EC-IC) bypass. Nevertheless, advances in imaging, assessment of cerebral hemodynamics, and surgical technique have changed the risk-benefit calculus for EC-IC bypass. New variations of revascularization surgery involving multiple anastomoses, flow preserving solutions, IC-IC constructs, and posterior circulation bypasses have been pioneered for otherwise difficult to treat pathology including giant aneurysms, dolichoectasia, and medically refractory intracranial atherosclerosis. This review provides a practical update on recent advances in adult intracranial bypass surgery.

Surgical revascularization of frontal areas in pediatric Moyamoya vasculopathy: a systematic review

INTRODUCTION

The aim of this study is to systematically review the literature on surgical revascularization techniques for flow-augmentation of the frontal areas and/or anterior cerebral artery (ACA) territory in children with Moyamoya vasculopathy (MMV), to elucidate the current surgical practice and describe the outcome associated to the different techniques.

EVIDENCE ACQUISITION

The systematic review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. MEDLINE, Web of Science and EMBASE were searched up to April 2020. Published techniques were systematically analyzed according to level of evidence, revascularization technique, opening of the interhemispheric fissure (IF), uni- or bilateral revascularization, clinical, neurocognitive, angiographic, perfusion and hemodynamic outcome.

EVIDENCE SYNTHESIS

Twenty-five studies were enrolled, including 829 patients: among these, 13 patients underwent direct revascularization of ACA territories, 570 indirect revascularization and 246 patients combined revascularization. One study reached a level of evidence II (grade of recommendation B), 8 studies were level III (grade B) and 16 studies were level IV (grade C). The surgical techniques proposed in the enrolled papers were systematically described.

CONCLUSIONS

Combined techniques (grade of recommendation B) and indirect techniques (grade of recommendation C) are considered effective for revascularizing the frontal areas and/or anterior cerebral artery (ACA) territory in children with MMV. While performing the revascularization, surgical risks can be reduced by avoiding the exposure of the superior sagittal sinus and opening of IF (recommendation grade C). There is not sufficient evidence to define which type of surgical technique should be preferred. Future studies are needed for a longitudinal assessment of comparable outcomes and to determine which revascularization technique for the frontal areas and/or ACA territory is optimal for this highly specific pediatric population.

Flow-augmentation bypass in the treatment of acute ischemic stroke

INTRODUCTION

Results of two randomized trials did not show benefit of revascularization with extracranial-intracranial (EC-IC) flow augmentation bypass in patients with symptomatic occlusion of internal carotid artery (ICA). However, patients with acute stroke were not included in these studies. Herein, we systematically analyze and discuss the literature about flow augmentation bypass for treatment of acute ischemic stroke.

EVIDENCE ACQUISITION

This systematic review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. MEDLINE, Web of Science and EMBASE were independently searched by two reviewers for published series to identify literature relating to EC-IC bypass in the surgical management of acute ischemic stroke up to June 2020. Studies were categorized according to their level of evidence.

EVIDENCE SYNTHESIS

Nineteen studies met the inclusion criteria for the systematic literature review, including 16 level IV studies (ten case series and six6 case reports) and three level III studies (retrospective cohort case-control studies). Occurrence of fatal or non-fatal ischemic or hemorrhagic postoperative stroke, as well as clinical functional outcome at follow-up were considered as primary and secondary endpoints, respectively.

CONCLUSIONS

The literature about flow augmentation bypass for treatment of acute ischemic stroke is scarce and heterogenous, with only 19 studies. The results of the present systematic review encourage further study to explore and validate the use of EC-IC bypass in the treatment of anterior circulation acute ischemic stroke in highly selected patients (symptomatic and with persistent penumbra despite best medical/endovascular treatment).

A critical appraisal of bypass surgery in moyamoya disease

Moyamoya disease (MMD) is a complex cerebrovascular disorder about which little is known. Conventionally, revascularization surgery is recommended for patients, despite an absence of conclusive data from adequate clinical trials. Underscoring the uncertainty that exists in treating MMD patients, investigators continue to present data comparing revascularization with conservative or medical management, most of which originates from East Asia where MMD is most prevalent. The purpose of this manuscript is to review contemporary large case series, randomized trials, and recent meta-analyses that compare surgical and medical treatments in adult patients with MMD, and to critically analyze the modern literature in the context of current practice standards. Data from the available literature is limited, but revascularization seems superior to conservative therapy in adult patients presenting with hemorrhage, and in preventing future hemorrhages. Conversely, evidence that surgery is superior to medical therapy is not convincing in adult patients presenting with cerebral ischemia, or for the prevention of future ischemic events. In contrast to East Asian populations, MMD in Europe and in the Americas is predominantly an ischemic disease that presents in adulthood. Adequate multinational trials are warranted.

Quantitative Angiographic Hemodynamic Evaluation After Revascularization Surgery for Moyamoya Disease

The corresponding hemodynamic changes of the internal carotid artery (ICA) after the revascularization surgery for moyamoya disease (MMD) remain unclear. The aim of this study was to analyze the hemodynamic changes of the ipsilateral ICA after the combined direct and indirect extracranial-intracranial (EC-IC) bypass. MMD patients undergoing combined EC-IC bypass were retrospectively reviewed. The mean transit time (MTT) of ICA was evaluated by color-coding angiography before revascularization and at follow-up. The MTT defined as the blood transit time between the end of cervical portion (C1) and the C7 segment of ICA. The clinical prognosis was assessed with Matsushima grading system, moyamoya vessel reduction system, and modified Rankin Scale (mRS). The correlation between hemodynamic parameter and prognosis was analyzed. Subgroup analysis was conducted between different presentations and different ages. Fifty-one patients were identified and the mean imaging follow-up interval was 5.5 months. The ICA-MTT was increased after the combined revascularization (P < 0.001) compared with contralateral ICA. Faster preoperative ICA-MTT was significantly associated with improved mRS in the ischemic group (P = 0.05). The increased ICA-MTT was significantly associated with favorable neoangiogenesis (P = 0.04), moyamoya vessel reduction (> 50%) (P = 0.023), and improved mRS score (P = 0.008). In subgroup analysis, the correlation in the ischemic subgroup and adult subgroup remained significant. In this cohort, the ICA-MTT increased after the combined EC-IC bypass, and there was a positive correlation between the increased blood transit time and favorable outcomes. Color-coding DSA proved to be useful as a quantitative and serial method to monitor postoperative courses after revascularization in MMD.

“BONNET” BYPASS IN BRAIN REVASCULARISATION

The article describes the “bonnet” bypass, the type of extracranial-intracranial bypass. This technique is performed when ipsilateral arteries can’t be used as a donor when cerebral revascularization is required. The literature was analyzed and three main techniques of “bonnet” have been defined. The indications for performing “bonnet” bypass are determined, and the disadvantages are indicated. Alternative methods of revascularization are presented and technical details of graft protection are described. The “bonnet” bypass is a rare and laborious technique of cerebral revascularisation. However, it is an alternative and effective method of treatment to prevent serious ischemic disorders.