经颅多普勒超声对颅外段颈内动脉狭窄诊断价值的评估

目的评价经颅多普勒超声(TCD)对颅外段颈内动脉(ICA)狭窄、闭塞的诊断价值及探讨TCD评价动脉狭窄程度的参数。方法对临床有缺血性脑血管病症状的患者,先做TCD检查,筛选出可疑有颅外段颈内动脉病变的患者．再行数字减影血管造影(DSA)及(或)多层面螺旋CT血管成像(CTA)检查,确定颅外段颈内动脉狭窄的诊断,并计算狭窄程度,然后将DSA／CTA证实颈内动脉狭窄的患者的TCD资料进行回顾性分析。结果(1)脑血流速度:单侧ICA闭塞患者,ICA血流信号消失或极低(<20cm／s);重度狭窄者,狭窄程度与流速呈正比:狭窄程度越重,收缩期峰值流速(PSV)增高越明显;中度狭窄者局部流速轻度增加;轻度狭窄者血流速度与正常流速比较无明显变化。(2)ICA狭窄段PSV与ICA狭窄远端PSV的比值:重度狭窄为3．13-4．56,中度狭窄为2．24-2．73,轻度狭窄无明显变化。(3)侧支循环开放:颈动脉完全闭塞中93．1％侧支循环开放,狭窄程度>90％者86．6％存在侧支循环开放,70％-90％狭窄者74．3％侧支循环开放,轻、中度狭窄者无1例侧支循环开放。(4)频谱图形:重度狭窄患者,TCD表现为频谱增宽、湍流改变;中度狭窄者可出现涡流改变;轻度狭窄者TCD仅表现为层流消失,频谱呈高强度血流充填信号,声频钝。结论TCD对颅外段ICA重度狭窄、闭塞的患者具有较高的诊断价值．可为介入治疗或手术治疗提供参考依据。     

症状性颈内动脉重度狭窄或闭塞患者的侧支循环评估

目的 探讨症状性颈内动脉重度狭窄或闭塞患者的侧支循环评估。方法 选取中国人民解放军火箭军总医院(原第二炮兵总医院)神经内科住院的症状性颈内动脉重度狭窄或闭塞患者41例,首先采用德国EME公司TC-2000S型经颅彩超多普勒(Transcranial Doppler,TCD)仪,常规检测双侧颈总动脉及颈内动脉、颅内Willis环及相关主要动脉分支,进行侧支循环评估; 进一步采用德国西门子64层螺旋CT扫描机行CT血管成像(CT angiography in diagnosis,CTA)检查,明确颈内动脉病变的存在; 再应用PHILIPS FD20 DSA数字减影机行全脑血管造影术并进行侧支循环评估,评估颈内动脉闭塞性病变后的侧支循环代偿能力,评估眼动脉侧支循环通路的开放情况及作用。结果 41例患者颈内动脉重度狭窄24例,颈内动脉闭塞17例。TCD显示ACoA开放5例,占12.2%,DSA为4例,占9.76%; TCD显示PCoA开放5例,占12.20%,DSA为3例,占7.32%; TCD判断OA开放25例,占60.98%,DSA为23例,占56.11%; TCD提示LA开放3例,占7.32%,DSA提示2例,占4.88%; TCD显示无侧支循环开放者16例,占39%,DSA为14例,占34.15%。TCD和DSA在评估侧支血管开放数量方面无显著差异(P>0.05)。TCD评估眼动脉开放在颈内动脉重度狭窄和闭塞的患者中有显著差异(P<0.05)。颈内动脉重度狭窄患者和闭塞患者的TCD及DSA侧支循环评估无显著差异(P>0.05)。OA单独开放患者较无OA开放患者PI值高。狭窄组MCA的PI值低于闭塞组,狭窄组OA最高流速低于闭塞组(P<0.05)。颈内动脉狭窄组OA单独开放数量<闭塞组(P<0.05)。结论(1)TCD与DSA在评估侧支循环血管开放数量方面的作用基本一致,TCD可作为CTA和DSA侧支评估之前的初筛手段,可以独立作为侧支循环评估的检查手段;(2)眼动脉是否参与侧支循环及眼动脉的的开放程度与颈内动脉本身病变程度有关。眼动脉作为次级侧支通路参与侧支循环的程度与病情严重程度具有一定相关性,在颈内动脉慢性闭塞性患者眼动脉单独开放的比例>重度狭窄的患者,重度狭窄的患者OA最高流速低于闭塞组患者,这说明颈内动脉慢性闭塞性患者其OA开放后提供的灌注代偿作用相对更大。     

颈动脉海绵窦瘘的经颅多普勒超声研究

采用彩色三维经颅多普勒观察18例颈动脉海绵窦瘘血流情况，发现其引流静脉多以眼上静脉为主、患侧颈内动脉流速明显高于健侧，患慎MCA，ACA流速低于健侧，压迫患侧颈总动脉，患侧颈内动脉(痿口以上)出现不同程度的倒灌血流。眼上静脉动脉化且血流反向的频谱特点及患侧颈内动脉倒灌血流为颈内动脉海绵窦瘘的特征性表现。经眶窗检测颈内动脉虹吸段时，其流速受瘘口所在位置的影响。观察颅内盗血情况可粗略估价瘘口大小。经颅多普勒检测颈动脉海绵窦瘘还可了解病人Willis环代偿能力，为必要时行一侧颈内动脉闭塞提供参考依据。     

外伤性颈内动脉海绵窦瘘患者介入治疗的血液动力学分析

目的 应用经颅多普勒超声（TCD）观察外伤性颈内动脉海绵窦瘘（CCF）患者介入治疗（可脱式球囊栓塞术）前后的血液动力学变化。方法 回顾分析2000年2月至2007年10月间介入治疗的18例外伤性CCF患者的TCD结果,并将手术前后的TCD与数字减影血管造影术（DSA）的检查结果进行比较。结果 经DSA证实的18例CCF患者15例行可脱式球囊栓塞术,DSA证实手术一次成功;2例术中改为ICA闭塞术,术后DSA显示患侧ICA完全闭塞;另1例术中出现血管痉挛而被迫放弃手术。术前TCD检测：（1）17例患侧颈内动脉颅外段和（或）颈内动脉虹吸段血流速度加快,脉动指数（PI）值均减低,其中颈内动脉虹吸段加快者伴频谱紊乱。（2）10例患侧大脑中动脉（MCA）、16例患侧大脑前动脉（ACA）血流速度减慢伴PI值下降。（3）11例患侧大脑后动脉（PCA）、14例健侧ACA流速加快,频谱形态正常。（4）16例患侧、2例双侧眼上静脉（SOV）呈现反向的静脉动脉化频谱。术后1周及6个月后复查TCD显示,15例球囊栓塞患者术前异常的颈内动脉及SOV等血管的血液动力学参数均恢复或接近正常,2例行ICA闭塞术患者TCD显示患侧ICA完全闭塞（患侧大脑后动脉及健侧大脑前动脉流速加快）。结论 TCD可以实时、动态的观察CCF患者颅内、外血管的血流及频谱改变,为临床提供可靠的血液动力学信息。     

颈动脉-海绵窦瘘的经颅多普勒超声研究

采用彩色三维经颅多普勒超声观察18例颈动脉-海绵窦瘘血流情况,发现其引流静脉多以眼上静脉为主,患侧颈内动脉流速明显高于健侧;患侧MCA、ACA流速低于健侧;压迫患侧颈总动脉,患侧颈内动脉(瘘口以上)出现不同程度的倒灌血流,眼上静脉的动脉化且血流反向的频谱特征为颈动脉-海绵窦瘘最典型的表现,其流速与瘘口大小,引流路径及流量的高低相关.经眶窗检测颈内动脉虹吸段时,其流速受瘘口所在位置的影响,观察颅内盗血情况可粗略估计瘘口大小.TCD检测颈动脉-海绵窦瘘还可了解病人 Willis环代偿能力,为必要时行一侧颈内动脉闭塞提供客观依据.     

颈动脉-海绵窦瘘的经颅多普勒超声研究

采用彩色三维经颅多普勒超声观察18例颈动脉-海绵窦瘘血流情况，发现其引流静脉多以眼上静脉为主．患侧颈内动脉流速明显高于健侧；患侧MCA、ACA流速低于健侧；压迫患侧颈总动脉，患侧颈内动脉(瘘口以上)出现不同程度的倒灌血流，眼上静脉的动脉化且血流反向的频谱特征为颈动脉-海绵窦瘘最典型的表现．其流速与瘘口大小，引流路径及流量的高低相关。经眶窗检测颈内动脉虹吸段时，其流速受瘘口所在位置的影响，观察颅内盗血情况可粗略估计瘘口大小．TCD检测颈动脉-海绵窦瘘还可了解病人Willis环代偿能力，为必要时行一侧颈内动脉闭塞提供客观依据。     

经颅多普勒对分水岭脑梗死的检查评价

目的探讨经颅多普勒对分水岭脑梗死的临床使用价值。方法所有病例均行头MRI、TCD以及主动脉弓、全脑血管造影（DSA）检查,并证实为分水岭脑梗死。结果一侧颈内动脉系统狭窄或闭塞的10例患者中TCD示6例患侧ACA1血流方向逆转,4例患侧OA血流方向逆转,7例健侧ACA,血流速度高于患侧,6例患侧PCA血流速度增快;14例大脑中动脉主干或上干狭窄或闭塞的患者中TCD示6例大脑中动脉阶段性高流速,6例大脑中动脉未探及血流,2例大脑中动脉低流速伴高PI;1例一侧颈内动脉系统轻度狭窄的患者TCD无明显的变化。结论经颅多普勒能够有效地评价分水岭脑梗死患者脑血管狭窄和侧枝循环的代偿情况。     

经颅多普勒量化评估单侧颈内动脉重度狭窄或闭塞侧支循环的可行性

目的探讨经颅多普勒(TCD)量化评估单侧颈内动脉(ICA)重度狭窄或闭塞侧支循环的可行性。方法经多模式影像证实为单侧ICA重度狭窄或闭塞者145例,用TCD及DSA评估侧支循环,并行一致性检验。对结果一致的128例进一步行TCD侧支循环量化评分,设定前交通动脉(ACo A)开放3分、后交通动脉(PCo A)开放2分、眼动脉(OA)开放1分。将128例患者分症状组及无症状组,对两组侧支循环评分行受试者工作特征曲线(ROC)分析。以诊断最佳界值为截点分侧支循环不良组及良好组,比较两组患侧TCD及CT灌注(CTP)参数,并与Alberta卒中项目早期CT评分(ASPECTS)行相关性分析。结果 (1) TCD评估ACo A、PCo A、OA与DSA的一致性均极佳(Kappa值=0.879、0.787、0.770,P 0.05)。(2)症状组与无症状组侧支循环评分间差异具有显著性(P 0.05)。(3) TCD侧支循环评分3.5分为诊断最佳界值,敏感度为73.7%,特异度为84.4%。(4) TCD及CTP参数:侧支循环不良组患侧大脑中动脉的平均流速、基底节区及颞叶的脑血流量和脑血容量均明显低于侧支循环良好组,而平均通过时间和达峰时间较侧支循环良好组明显延长(均P 0.05)。(5) TCD侧支循环评分与ASPECTS呈高度正相关(r=0.767,P 0.05)。结论 TCD可以量化评估单侧ICA重度狭窄或闭塞病变的脑侧支循环,对临床诊疗具有指导意义。     

颈动脉闭塞性血管病的颅内脑血流改变与临床表现的关系

目的　分析颈内动脉严重狭窄 (狭窄≥ 75 % )或闭塞患者 (ICASO)颅内脑血流改变与临床表现的关系。方法　经全脑数字减影血管造影 (DSA)检查证实的ICASO患者 66例 (单侧病变 5 0例 ,双侧 16例 )。临床分为脑梗死组、TIA组和无体征组。应用经颅多谱勒超声 (TCD)检测双侧大脑中动脉 (MCA)血流速度 (Vmca)并判断颅内侧枝循环的开放。结果　①与DSA比较TCD对前交通动脉 (ACOA)判断的敏感性 97% ,特异性 93 % ;后交通动脉 (PCOA)敏感性 92 % ,特异性83 % ;眼动脉 (OA)开放的敏感性 98% ,特异性 90 %。无体征组和TIA组ACOA和PCOA同时存在的出现率高 ,而脑梗死组则仅有OA存在的出现率最高。②狭窄同侧Vmca(3 9 5 5± 13 2 8)cm/s明显低于对侧 (78 90± 2 4 15 )cm/s(P <0 0 1) ,频谱低平呈波浪状。脑梗死组低于TIA组和无症状组 (P <0 0 5 )。结论　TCD可以无创性地检测颈内动脉严重狭窄或闭塞后脑血流动力学的改变 ,并与临床表现相关。前后交通动脉代偿良好时不易出现脑梗死 ;仅有眼动脉反向存在及大脑中动脉血流速度的明显降低往往提示代偿不足 ,易发生缺血性病变。     

颈内动脉严重狭窄时脑部症状与Willis环侧支循环建立的关系

目的应用经颅超声多普勒(TCD)检测颈内动脉(ICA)严重狭窄,探讨Willis环的侧支循环与临床症状之间的相关性.方法分析34例ICA严重狭窄患者(其中有症状组16例和无症状组18例)侧支循环的类型、大脑中动脉(MCA)的平均血流速度(Vm)、脉动指数(PI)及频谱改变,并与30例正常人进行对照.结果存在3种侧支循环类型前交通动脉(ACOA)型,后交通动脉(PCOA)型,眼动脉(OA)型.无症状组的侧支循环中,ACOA型占88.9%,狭窄侧MCA Vm为59.1±8.7cm/s;有症状组ACOA型占50%,有4例未检出侧支循环,狭窄侧MCA Vm为48.6±7.3cm/s(P＜O.OO1).所有患者狭窄侧的MCA PI减低(p＜O.001),且频谱低平呈波浪状,波峰变钝,失去收缩峰的特征.结论TCD可以发现ICA严重狭窄患者Willis环侧支循环的显著异常改变,研究Willis环的侧支循环对ICA产重狭窄患者治疗和授后的判断其有重要的临床价值.     

Ophthalmic Artery Flow Direction on Color Flow Duplex Imaging Is Highly Specific for Severe Carotid Stenosis

BACKGROUND/PURPOSE: Collateral flow patterns are important risk factors for brain ischemia in the presence of internal carotid artery (ICA) stenosis or occlusion. Ophthalmic artery (OA) flow reversal, routinely studied by transcranial Doppler sonography, is an important marker for high-grade ICA stenosis or occlusion. The authors sought to define the value of assessing OA flow direction with color flow duplex ultrasonography (CDUS) in the setting of significant ICA disease. METHODS: Of all patients having routine carotid ultrasound in the neurosonology laboratory between July 1995 and November 2000, 152 had both carotid and orbital (OA flow direction by reduced power orbital CDUS) examinations as well as angiographic confirmation of stenosis to which North American Symptomatic Carotid Endarterectomy Trial criteria could be applied. Degree of angiographic stenosis in these 152 patients (304 arteries) was correlated with OA flow direction. RESULTS: Of 304 arteries, 101 had greater than 80% stenosis by angiogram. In 56 of these 101 arteries with high-grade stenosis or occlusion, the ipsilateral OA was reversed; however, OA flow direction was never reversed ipsilateral to arteries with less than 80% stenosis (sensitivity 55%, specificity 100%, negative predictive value 82%, and positive predictive value 100% for OA flow reversal as a marker of high-grade carotid lesions). DISCUSSION/CONCLUSIONS: OA flow direction is easily studied with CDUS. Reversed OA flow direction is highly specific (100%) for severe ipsilateral ICA stenosis or occlusion, with excellent positive predictive value, moderate negative predictive value, and limited sensitivity. OA flow reversal is not only quite specific for severe ICA disease, which may be helpful if the carotid CDUS is difficult or inadequate, but may also provide additional hemodynamic insights (i.e., the inadequacy of other collateral channels such as the anterior communicating artery). OA evaluation can provide important hemodynamic information and should be included as part of carotid CDUS if there is any evidence of ICA stenosis or occlusion.     

颈内动脉重度狭窄或闭塞患者的侧支循环与神经功能的单因素分析

目的 探讨颈内动脉重度狭窄或闭塞患者侧支循环的代偿作用与临床神经功能缺损程度的关系. 方法对52例连续颈内动脉狭窄或闭塞所致的脑梗死患者入院时行神经功能缺损评分(NIHSS)评分,利用数字减影脑血管造影技术(DSA)评估颅内动脉的侧支循环代偿情况.应用统计学方法探讨两者之间的关系.结果 DSA发现52例患者18例出现颈内动脉闭塞,单侧颈内动脉重度狭窄28例,6例双侧重度狭窄.52例患者中出现前交通动脉代偿18例,后交通动脉代偿8例,前后交通动脉同时代偿12例,14例患者未出现Willis环血管的代偿.无Willis环代偿组与Willis环代偿组NIHSS评分平均秩次分别为35.75和23.09,两组差异有统计学意义(P<0.05).前交通代偿组与后交通代偿组NIHSS评分平均秩次分别为12.42和15.94,两组差异无统计学意义(P<0.05).结论颈内动脉狭窄或闭塞时可通过多种方式进行有效的代偿.NIHSS评分与血管代偿及阻塞位置显著有关.DSA对侧支循环的判定在治疗干预中显得尤为重要.     

Specific transcranial Doppler flow findings related to the presence and site of arterial occlusion

BACKGROUND AND PURPOSE: Transcranial Doppler (TCD) can localize arterial occlusion in stroke patients. Our aim was to evaluate the frequency of specific TCD flow findings with different sites of arterial occlusion. METHODS: Using a standard insonation protocol, we prospectively evaluated the frequency of specific TCD findings in patients with or without proximal extracranial or intracranial occlusion determined by digital subtraction or MR angiography. RESULTS: Of 190 consecutive patients studied, angiography showed occlusion in 48 patients. With proximal internal carotid artery (ICA) occlusion, TCD showed abnormal middle cerebral artery (MCA) waveforms (AMCAW) in 66.7%, reversed ophthalmic artery (OA) in 70.6%, anterior cross-filling via anterior communicating artery (ACoA) in 78.6%, posterior communicating artery (PCoA) in 71.4%, and contralateral compensatory velocity increase (CVI) in 84.6% of patients. With distal ICA occlusion, TCD showed AMCAW in 88.9%, OA in 16.7%, ACoA in 50%, PCoA in 60%, and CVI in 88.9% of patients. With MCA occlusion, TCD showed AMCAW in 100%, OA in 23.5%, ACoA in 31.3%, PCoA in 23.1%, and CVI in 62.5%. With no anterior circulation occlusion at angiography, TCD showed these parameters in 1.8% to 17. 9%, chi(2) P相似文献   

Clinical significance of the ophthalmic artery in carotid artery disease

A total of 141 subjects with tight stenosis (≥75%) or occlusion of internal carotid artery were followed up at intervals 3–6 months regularly for 40 ± 16 months. The direction of ophthalmic artery flow was used as a parameter of risk indicator on cerebral ischemic events. Eleven patients with bilateral carotid tight stenosis/occlusion were excluded in the analysis. Thus, the 130 carotid arteries were divided into three groups: (1) carotid artery with ipsilateral hemispheric TIA or stroke (85 patients), (2) carotid arteries with contralateral hemispheric TIA/stroke or VBI (15 patients), and (3) carotid arteries of asymptomatic patients (30 patients). The symptomatic carotid artery group (group 1) had significantly more often reversed ophthalmic flow than the other two groups (group 2 and 3, p < 0.001). During follow-up prospectively for four years, 41 patients had cerebral ischemic events, three had cardiac ischemic events and six died of malignancy. Patients with reversed OA flow had more often subsequent cerebral ischemic events than those with forward flow (27 vs 14, p = 0.010). However, the difference remained significant only in the asymptomatic patients (group 3, 4 vs 0, P < 0.001), not for groups 1 and 2, after further analysis. Our work supported that the clinical role of ophthalmic artery collateral varied between asymptomatic and symptomatic patients.     

10例双侧颈动脉重度狭窄或闭塞患者的临床特点分析

目的探讨双侧颈动脉重度狭窄或闭塞患者的临床特点。方法回顾性分析10例双侧动脉重度狭窄或闭塞患者临床特点及血流代偿情况。结果 10例患者中,双侧颈总动脉闭塞和颈内动脉闭塞各1例,双侧颈内动脉重度狭窄5例,一侧闭塞合并一侧重度狭窄3例。临床表现为后循环缺血5例,后循环合并前循环缺血3例,前循环缺血2例。7例行DSA患者,有7例后交通动脉开放,4例前交通动脉开放。结论双侧颈动脉重度狭窄或闭塞患者临床表现以后循环缺血多见,后交通动脉可能为其主要代偿模式。     

Diagnostic criteria for transcranial colour-coded duplex sonography evaluation of cross-flow through the circle of Willis in unilateral obstructive carotid artery disease

A transcranial colourcoded duplex sonography (TCCD) study was performed to establish reliable criteria for the assessment of collateral flow through the anterior (ACoA) and posterior (PCoA) communicating artery without using compression tests. We studied 86 patients with angiographically evaluated unilateral > 69% stenosis (n = 53) and occlusion (n = 33) of the carotid artery. The following TCCD criteria were evaluated: for diagnosis of cross-flow through the ACoA, detection of reversed flow in the anterior cerebral artery (ACA) on the obstructed (ipsilateral) side. For the diagnosis of cross-flow through the PCoA: (A) identification of the PCoA; (B) peak systolic velocity in P1 posterior cerebral artery (PCA) higher than the mean value + 2 SD of normals; (C) ratio of ipsilateral peak systolic P1 PCA velocity to peak systolic P2 PCA velocity higher than the mean ratio + 2 SD of normals; (D) ratio of ipsilateral peak systolic PI PCA velocity to contralateral peak systolic P1 PCA velocity higher than the mean ratio – 2 SD of normals; (E) peak systolic basilar artery velocity higher than the mean value + 2 SD of normals. Eight patients (9%) with inadequate temporal ultrasonic windows were excluded. The sensitivity and specificity for TCCD evaluation of ACoA crossflow were 100%. Using criteria A and B the corresponding values for the PCoA were 85 and 98%, respectively. Criteria C-E were not useful owing to lower sensitivity. In conclusion, we delineated TCCD criteria that make it possible to assess reliably the cross-flow through the circle of Willis in patients with adequate ultrasonic windows.     

Transcranial Doppler findings during balloon test occlusion of the internal carotid artery.

The authors performed transcranial Doppler ultrasonography (TCD) during internal carotid artery (ICA) balloon test occlusion (BTO) and observed changes in mean flow velocity (Vm) in the middle cerebral artery (MCA), and pulsatility index (PI) while monitoring the stump pressure (Sp) of the internal carotid artery (ICA), and neurologic findings. A group of 17 patients requiring possible temporary or permanent occlusion of the ICA in the course of planned procedures first underwent BTO. A patient who either developed neurologic changes or maintained less than 60% of preocclusion Sp or Vm in the ipsilateral MCA during BTO was considered to have a positive test. Eleven patients had negative results, while in six patients, tests were positive. Mean flow velocity showed a decrease after occlusion in all cases but not to a remarkable extent in some patients. Stump pressure decreased in all negative cases after balloon inflation and than tended to increase progressively during 15 minutes of BTO. Pulsatility index tended to decrease gradually during BTO in all negative patients. However, in positive cases, PI and Sp fell steeply. Only one positive case had a neurologic symptom of severe headache. The decreased PI in the MCA reflected autoregulatory dilation of cerebral vessels to compensate for decreased absolute cerebral blood volume following ICA occlusion. Changes in PI are a good indicator for evaluating blood flow during BTO.     

Borderzone hemodynamics in cerebrovascular disease

To investigate the possible existence of chronic selective hemodynamic impairment in the arterial borderzone regions of the brain, we used positron emission tomography (PET) to measure regional mean vascular transit time (rt, equal to the ratio of regional cerebral blood volume to cerebral blood flow) and regional oxygen extraction fraction (rOEF) in 32 patients with either severe internal carotid artery stenosis or occlusion and 11 normal controls. Twenty-four of the patients had had TIAs or amaurosis fugax from 1 to 60 days before PET; all had normal brain CT. We used a stereotactic localization method to locate the anterior and posterior borderzone regions of the middle cerebral artery (MCA) territory. We then calculated ratios of each borderzone to the ipsilateral MCA territory for both rt and rOEF. There was no significant difference from control ratios in any patient subgroup including those with greater than or equal to 75% stenosis or occlusion, those with or without contralateral greater than or equal to 50% stenosis, or those with abnormal hemodynamics in the MCA territory. We therefore found no evidence for selective borderzone hemodynamic impairment in this group of patients with severe carotid artery disease.     

Volume flow rate evaluation in patients with obstructive arteriosclerotic disease

This study was performed to quantify the volumetric impact of extracranial arteriosclerotic lesions. We investigated patients with different degrees of carotid stenosis as defined by conventional velocity-based duplex criteria and different patterns of collateralization. We studied the volume flow rate (color duplex M-mode device) in 37 patients with symmetrical internal carotid artery (ICA) plaques (<50% stenosis) and compared these data to 43 patients with a unilateral 50-74% stenosis, 75-99% stenosis (n = 73) and occlusion of the ICA (n = 37). A 75-99% stenosis caused an ipsilateral flow reduction of 36% with a wide interindividual variability, and an occlusion of 51%. Collateralization via the ophthalmic artery only caused a nonsignificant ipsilateral volume flow increase, whereas the contralateral volume flow was significantly higher in patients with a patent anterior communicating artery. The increase was more pronounced in patients with an occluded vessel. Our data demonstrate a wide diversity of the hemodynamic impact of carotid stenosis as defined by 'classical' Doppler criteria. Collateral flow reflects a dynamic quantitative process.