Effect of collateral flow patterns on outcome of carotid occlusion

Subarachnoid Hemorrhage and Internal Carotid Artery Dissection and Occlusion Following Self-Enucleation

Self-enucleation is an uncommon type of major self-injury, which may lead to severe neurological deficits and life-threatening complications, such as subarachnoid hemorrhage (SAH) and internal carotid artery (ICA) dissection and occlusion. Our patient is a 53-year-old man with a history of bipolar disorder and schizophrenia who presented with SAH, intraventricular hemorrhage, ICA dissection and occlusion, and right cerebral infarct following self-enucleation. Despite a Glasgow Coma Score of 6 on initial presentation, he improved with conservative management. He achieved a near-complete neurological recovery, with residual left lower extremity weakness and mild confusion. Self-enucleation is a major neurologic, ophthalmologic, and psychiatric emergency with a potential for serious neurological complications and contralateral visual loss. Yet, conservative management may lead to dramatic recovery.

Influence of the circle of Willis on leptomeningeal collateral flow in anterior circulation occlusive stroke: Friend or foe?

BACKGROUND

Clinical outcome after large vessel occlusion (LVO) stroke depends on collateral integrity. We aimed to evaluate whether the completeness of the circle of Willis (CoW) and anterior temporal artery (ATA) determines the status of leptomeningeal collaterals (LC) in patients with acute LVO (internal carotid artery (ICA) and middle cerebral artery M1 (MCA) occlusion) treated with endovascular thrombectomy.

PATIENTS AND METHODS

LC, cross-flow through the anterior communicating artery (ACoA), presence of the ipsilateral posterior communicating artery (IpsiPCoA) and presence of the ATA were evaluated using CT angiography. LC was graded as good when ≥50% collateral filling was noted compared to the unaffected hemisphere.

RESULTS

We included 159 patients with a median age of 75 years (IQR 63-82), MCA M1 occlusion in 96 (60%) and good outcome in 68 (45.6%). The LC were good in 129 (81.1%) patients. Complete IpsiPCoA and incomplete ACoA status was inversely associated with good LC in LVO (OR 0.51 (95% CI 0.02-0.07)). A complete CoW was associated with good LC in ICA occlusions, OR 8.4 (p = .025). Good outcome (modified Rankin scale 0-2 at 3 months) was associated with good LC (OR 5.63 (95% CI 1.11-28.4)), small ischemic lesion volume (OR 0.94 (95% CI 0.97-0.98)) and absence of the ACoA and IpsiPCoA (OR 4.47 (95% CI 1.09-18.3)).

CONCLUSIONS

ATA presence was associated with good leptomeningeal collaterals in LVO (OR 8.13 (95% CI 1.69-39.0)) and in MCA M1 patients (OR 7.9 (95% CI 1.7-36.4)). The effect of ATA was most pronounced in MCA M1 occlusions, and that of ACoA was most pronounced in ICA occlusions.

Altered Resting-State Cortical EEG Oscillations in Patients With Severe Asymptomatic Carotid Stenosis

Asymptomatic carotid stenosis is characterized by altered cerebral hemodynamics and cognitive impairment, but the underlying neurophysiological mechanism remains unclear. To elucidate the alterations of cortical activities, resting-state electrophysiological activities were recorded from patients with mild (<30%; n=10; age 57-85 years), moderate (30% to 50%; n=11; age 66-88 years), and severe (>50%; n=8; age 67-91 years) carotid stenosis. The current density and oscillatory power of the cortical sources were analyzed using the minimum norm estimates method combined with fast Fourier transform analysis. Our results indicate that the cortical current density among regions of the brain was similar, irrespective of the degree of carotid stenosis. With regard to the cortical oscillations, augmented theta activities in the bilateral parietal, left temporal, and left occipital regions and attenuated alpha activities in the bilateral frontal and right central regions were obtained in patients with severe asymptomatic carotid stenosis. We suggest that the source-based cortical oscillations at theta and alpha bands might reflect the alterations of the brain activities and characterize the altered neurophysiological mechanism of the brain with at least 50% occlusion of the carotid artery. Further longitudinal studies with larger populations are warranted to verify the present findings.

Correlation Between the Integrity of the Circle of Willis and the Severity of Initial Noncardiac Cerebral Infarction and Clinical Prognosis

The quality of collateral circulation affects the severity and prognosis of stroke patients. The effect of the circle of Willis, which is the primary collateral circulation, on ischemic stroke has attracted significant attention. This study was designed to investigate the effect of different circles of Willis types on stroke severity and prognosis in patients with noncardiac stroke.A total of 376 patients with noncardiac ischemic stroke, who were treated by the specialty team of cerebrovascular diseases at the First Affiliated Hospital of Sun Yat-sen Hospital, were successively enrolled in this study. The detailed clinical characteristics of the patients were recorded upon admission, including risk factors of vascular disease and National Institutes of Health Stroke Scale (NIHSS) scores. The patients were divided into groups of different circles of Willis types based on magnetic resonance angiography (MRA) that was performed within 3 days of admission-type I: complete circle of Willis; type II: complete anterior half of the circle of Willis and incomplete posterior half of the circle of Willis; type III: incomplete anterior half of the circle of Willis and complete posterior half of the circle of Willis; and type IV: incomplete anterior and posterior halves of the circle of Willis. Patients were re-evaluated for NIHSS scores at discharge and after discharge. The modified Rankin score (mRS) was recorded for 90 days, and stroke recurrence and death after 90 days were also recorded until the end of the study.The 376 patients were divided into 4 groups based on the MRA-type I group: 92 patients (24.5%); type II group: 215 patients (57.2%); type III group: 12 patients (3.2%), and type IV group: 57 patients (15.2%). NIHSS scores at admission and discharge were significantly lower for the type I group compared with those for the type II and type IV groups (P < 0.05). NIHSS scores were higher in the groups with an incomplete circle of Willis compared with the group with a complete circle of Willis. A poor recovery rate was highest for the type IV group, whereas a good recovery rate was highest for the type I group. The logistic regression analysis showed that a complete circle of Willis was one of the predictors of suitable recovery (odds ratio [OR] = 0.708, 95% confidence interval [CI]: 0.554-0.906).Circle of Willis type was associated with stroke severity and patient prognosis, whereas an incomplete circle of Willis was associated with more severe conditions and a higher 90-day poor diagnosis rate. A complete circle of Willis was an independent predictor of good prognosis.

The Paramount Role of the Anterior Communicating Artery in the Collateral Cerebral Circulation

Clinical manifestation of carotid occlusive disease is largely dependent on the severity of stenosis and the capability of collateral circulation. However, due to the complexity and difficulty in evaluation, cerebral collateral circulation has, so far, remained underappreciated. We report a patient with advanced extracranial arterial disease (including the right subclavian steal, occlusion of the right external carotid artery, and severe stenosis of the left vertebral artery), who underwent transient right internal carotid artery occlusion during carotid intervention. Throughout the occlusion, the flow into the right hemisphere (monitored by transcranial Doppler ultrasound in the right middle cerebral artery) was sufficient despite almost totally dependent on the anterior communicating artery, which highlights its role as the most potent collateral pathway.

Usefulness of transcranial Doppler ultrasound in evaluating cervical-cranial collateral circulations

Transcranial Doppler (TCD) ultrasound is a noninvasive, safe and cost-effective bedside test for evaluating cerebrovascular circulation in real time. It has been rapidly evolving from a simple noninvasive diagnostic tool to an imaging model with a broad spectrum of clinical applications. TCD can show the spectral flow waveforms, blood flow direction, velocities and intensity in the intracerebral vessels, adding physiologic information to other imaging models. TCD can also detect collateral channels through the anterior communicating artery, posterior communicating arteries, reversed ophthalmic artery, leptomeningeal collaterals, reversed basilar artery and reversed vertebral artery caused by hemodynamically significant carotid or intracranial stenosis. This article gives a brief overview of its use in evaluation of collateral circulation in carotid and intracranial steno-occlusive disease.

The genetics of ischaemic stroke

In this review, we discuss the genetic factors in both the aetiology and treatment of ischaemic stroke. We discuss candidate gene association studies, family linkage studies and the more recent whole genome association studies and whole genome expression studies. We also briefly discuss genetic testing for stroke risk and genetic analysis of treatment complications.

Dynamic cerebral autoregulation and collateral flow patterns in patients with severe carotid stenosis or occlusion

The quality of collateral blood supply in carotid disease is pivotal for the resulting hemodynamic compromise. However, the interrelation between different patterns of collateral blood flow and actual impairment of cerebral autoregulation (CAR) has not been analyzed so far. Dynamic CAR was assessed noninvasively by the phase shift between respiratory-induced 0.1-Hz oscillations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) in 101 patients with severe unilateral carotid stenosis (> or = 75%) or occlusion. CO(2)-vasomotor reactivity was assessed via inhalation of 7% CO(2). Spontaneously activated collaterals via primary (anterior/posterior communicating artery, type I, n = 65) and secondary (ophthalmic artery / leptomeningeal with or without primary pathways, group II, n = 24) pathways were assessed by transcranial Doppler/duplex sonography. Signs of functional stenosis in the anterior collateral pathways were subsumed under type III (n = 12). Best dynamic CAR (phase shift) on affected sides was observed for type I (n = 65), in which values did not differ significantly from contralateral sides. Reduced phase shift values were present in type II; poorest values were observed for type III. CO(2)-reactivity differed mainly between type I and the other types. A less distinct differentiation of autoregulatory impairment was found when dividing patients into groups of different degrees of stenosis. Symptomatic patients (previous TIA/stroke) were significantly less frequent in the group with type I collateral flow and had significantly lower phase shift and CO(2)-reactivity values. In conclusion, we found that dynamic CAR is substantially impaired if secondary collateral pathways are activated or if functional stenosis in the activated anterior collateral pathway is present. These hemodynamic constellations are also associated with a higher proportion of clinically symptomatic patients. Determination of dynamic CAR by transfer function analysis represents a convenient, sensitive method for detection of cerebral hemodynamic compromise in obstructive carotid disease.

Color velocity imaging quantification in the detection of intracranial collateral flow

BACKGROUND AND PURPOSE

The development of intracranial collateral circulation is associated with a lower risk of stroke. A noninvasive technique that can reliably detect the presence of intracranial collaterals would be a valuable factor in the assessment of risk in patients with occlusive cerebrovascular disease.

METHODS

Color velocity imaging quantification was used to measure the blood flow volume of the common carotid and vertebral arteries in 40 patients with carotid occlusive disease. The blood flow volumes in these arteries were correlated with angiographic evidence of collaterals to establish the best cutoffs for detecting intracranial collateral circulation.

RESULTS

A blood flow volume of either > or =370 mL/min in the common carotid artery or > or =120 mL/min in the vertebral artery was indicative of the presence of intracranial collaterals. The sensitivity and specificity for the common carotid artery were 92.3% [95% confidence interval (CI), 62.1 to 99.6] and 92.1% (95% CI, 77.5 to 97.9), respectively. The sensitivity and specificity for the vertebral artery were 75.0% (95% CI, 35.6 to 95.5) and 87.5% (95% CI, 66.5 to 96.7), respectively.

CONCLUSIONS

Color velocity imaging quantification offers a noninvasive, accurate method for detecting the presence of intracranial collateral circulation and quantifying its magnitude. This technique would be a useful adjunct in screening or continuous monitoring of patients with severe carotid occlusive disease.

Collateral ability of the circle of Willis in patients with unilateral internal carotid artery occlusion: border zone infarcts and clinical symptoms

BACKGROUND AND PURPOSE

The circle of Willis is regarded as the major source of collateral flow in patients with severe carotid artery disease. The purpose of the present study was to assess whether the presence of border zone infarcts is related to the collateral ability of the circle of Willis in symptomatic (transient ischemic attack, minor stroke) and asymptomatic patients with unilateral occlusion of the internal carotid artery (ICA).

METHODS

Fifty-one patients (35 symptomatic, 16 asymptomatic) and 53 control subjects were investigated. Patients had unilateral occlusion of the ICA and contralateral ICA stenosis between 0% and 69%. The directions of flow, on the side of the ICA occlusion, and the size of the component vessels in the circle of Willis were investigated with MR angiography.

RESULTS

On average, 92% of the patients without border zone infarcts (n=26) had willisian collateral flow compared with 60% of patients with border zone infarcts (n=25; P<0.05). This increase in collateral flow was caused by the high prevalence of collateral flow via the posterior communicating artery in patients without border zone infarcts (50% versus 12%; P<0.05). No statistically significant relation was found between the pattern of collateral flow via the circle of Willis and the presence of clinical symptoms. Nevertheless, asymptomatic patients with ICA occlusion demonstrated an increased diameter of the anterior communicating artery (P<0.05).

CONCLUSIONS

In patients with unilateral ICA occlusion, the presence of collateral flow via the posterior communicating artery in the circle of Willis is associated with a low prevalence of border zone infarcts. Asymptomatic patients with an ICA occlusion do not have an increased collateral function of the circle of Willis.

Effect of collateral blood flow and cerebral vasomotor reactivity on the outcome of carotid artery occlusion

BACKGROUND AND PURPOSE

Evidence suggests that an alteration in cerebral hemodynamics plays a relevant role in the occurrence of stroke in patients with carotid occlusion. The purpose of the present study was to evaluate the relationships among baseline characteristics, type and number of collateral pathways, cerebral vasomotor reactivity (VMR), and outcome of patients with carotid occlusion.

METHODS

One hundred four patients with symptomatic or asymptomatic internal carotid artery occlusion were followed up prospectively for a median period of 24 months. Cerebral VMR to apnea was calculated with transcranial Doppler ultrasonography by means of the breath-holding index (BHI) in the middle cerebral arteries. The patency of the 3 major intracranial collateral vessels was also evaluated.

RESULTS

During the follow-up period, 18 patients experienced an ischemic stroke ipsilateral to internal carotid artery occlusion. Among factors considered, only older age, number of collateral pathways, and BHI values in the middle cerebral artery ipsilateral to the occluded side were significantly associated with the risk of ipsilateral stroke (P<0.001, P=0.008, and P<0.001, respectively; multiple Cox regression analysis). A normal VMR and favorable prognosis characterized patients with full collateral development; in this group, no patient experienced an ischemic event. On the other hand, an impaired VMR and increased probability of experiencing a stroke were found in patients without collateral pathways; the annual risk of ipsilateral stroke in this group was 32.7%. Patients with 1 or 2 collateral pathways showed a different VMR ranging from normal to strongly reduced BHI values. The ipsilateral stroke event risk was 17.5% in patients with 1 collateral vessel and 2.7% in patients with 2 collateral pathways. In this case, the risk of cerebrovascular events occurring during the follow-up period was significantly related to VMR.

CONCLUSIONS

These data suggest that cerebral hemodynamic status in patients with carotid occlusive disease is influenced by both individual anatomic and functional characteristics. The planning of strategies to define the risk profile and any attempt to influence patients' outcome should be based on the evaluation of the intracranial hemodynamic adaptive status, with particular attention to the number of collateral vessels and the related VMR.

Clinical features associated with internal carotid artery occlusion do not correlate with MRA cerebropetal flow measurements

OBJECTIVES

The aetiology of clinical symptoms in patients with severe internal carotid artery (ICA) lesions may be thromboembolic or haemodynamic. The purpose was to assess whether changes in cerebropetal blood flow caused by an ICA occlusion have an effect on clinical symptoms and cerebral metabolism.

METHODS

Forty three patients with an ICA occlusion who had hemispheric ischaemia (transient ischaemic attack or stroke), retinal ischaemia, or without symptoms, and 34 patients without significant ICA lesions with either hemispheric ischaemia or no symptoms were studied. Magnetic resonance angiography (MRA) was used to investigate total cerebropetal flow (flow in the ICAs plus basilar artery) and the flow in the middle cerebral arteries. Cerebral metabolic changes in the flow territory of the middle cerebral artery were determined with proton MR spectroscopy.

RESULTS

Low total cerebropetal flow (r=-0.15, p<0.05) and low middle cerebral artery flow (r=-0.31, p<0.001) were found in patients with an ICA occlusion, but did not correlate with the clinical syndrome. By contrast, patients with prior symptoms of hemispheric ischaemia had decreased cerebral N-acetylaspartate/choline ratios (r=-0.35, p<0.001). However, the presence of an ICA occlusion (and subsequent low flow) did not correlate with low N-acetylaspartate/choline ratios.

CONCLUSION

Neurological deficit caused by (transient) hemispheric ischaemia is associated with low N-acetylaspartate/choline ratios, whereas prior clinical features are not associated with low cerebropetal blood flow, as measured with MR angiography. As a result, differences in cerebropetal flow cannot explain why patients with similar carotid artery disease experience different neurological features.

A longitudinal study of collateral flow patterns in the circle of Willis and the ophthalmic artery in patients with a symptomatic internal carotid artery occlusion

BACKGROUND AND PURPOSE

The purpose of the present study was to assess whether the direction of flow via the circle of Willis and the ophthalmic artery (OphA) changed over time in patients with a symptomatic occlusion of the internal carotid artery (ICA) who did not experience recurrent cerebral ischemic symptoms.

METHODS

Sixty-two patients with a symptomatic ICA occlusion were investigated within 6 months after symptoms occurred. The investigations were repeated after 6 and 12 months. The directions of flow in the A1 segment and the posterior communicating artery (PCoA), both on the side of the symptomatic ICA occlusion, were assessed with the use of magnetic resonance angiography. The pattern of collateral flow via the circle of Willis was categorized as via the A1 segment only, via the PCoA only, via the A1 segment plus the PCoA, or no collateral flow via the circle of Willis. The direction of flow in the OphA was investigated with transcranial Doppler sonography. CO(2) reactivity was determined with transcranial Doppler sonography to investigate whether changes in flow patterns were accompanied by changes in cerebrovascular reactivity.

RESULTS

There were no statistically significant changes over time in the direction of blood flow in the A1 segment and the PCoA or in the pattern of collateral flow via the circle of Willis. On average, 72% of patients with a unilateral ICA occlusion (n=41) had willisian collateral flow compared with 37% of patients with a bilateral ICA occlusion (n=21; P<0.05). Patients with a unilateral ICA occlusion tended to a lower prevalence of reversed flow via the OphA over time. CO(2) reactivity did not change significantly in any patient group. In patients with a unilateral ICA occlusion, decreased CO(2) reactivity was associated with a higher prevalence of absent willisian collateral flow and a lower prevalence of collateral flow via the A1 segment plus the PCoA.

CONCLUSIONS

The absence of recurrent cerebral ischemic symptoms in patients with a symptomatic ICA occlusion is not associated with an improvement in collateral flow via the circle of Willis or the OphA during 1.5-year follow-up.

Collateral variations in circle of willis in atherosclerotic population assessed by means of transcranial color-coded duplex ultrasonography

BACKGROUND AND PURPOSE

Transcranial color-coded duplex ultrasonography combined with common carotid artery (CCA) compression can be used to assess the collateral function of the circle of Willis. The aim of this study was to assess the unknown fraction of hemodynamic functional anterior and posterior communicating arteries (AcoA and PcoA, respectively) in an atherosclerotic population with no cerebrovascular symptoms.

METHODS

In 76 patients with a mean age of 61 (35 to 89) years, the blood flow velocity changes in the precommunicating parts (A1 and P1, respectively) of the anterior and posterior cerebral arteries were measured during CCA compression. The AcoA was defined as functional if blood flow was reversed in the ipsilateral A1 and enhanced in the contralateral A1 during CCA compression. The PcoA was defined as functional if the flow velocity in the P1 was enhanced >20% during ipsilateral CCA compression.

RESULTS

It was possible to assess cross flow through the anterior part of the circle of Willis in 95% of the subjects. Failure of this collateral pathway was caused by a hypofunctional AcoA in 4% and a hypofunctional A1 in 1% of the subjects. Anomalies in the posterior part of the circle of Willis hampering collateral flow from the basilar to the internal carotid artery were found in 45% of the hemispheres. Thirty-eight percent of PcoAs were hypofunctional, and 7% of the posterior cerebral arteries had a persistent fetal anatomy.

CONCLUSIONS

We found that in subjects with no cerebrovascular symptoms, the anterior collateral pathway of the circle of Willis was nearly always functional. In contrast, the posterior collateral pathway was nonfunctional in almost half of the total number of hemispheres. Comparing these basic data with data from patients with cerebral ischemic disease might further help to elucidate the importance of the collateral capacity of the circle of Willis.

Hemodynamic role of the circle of Willis in stenoses of internal carotid arteries. An analytical solution of a linear model

A mathematical model of blood flow through the circle of Willis was developed, within a linear framework. Comprehensive analytical solutions, including a remarkably small number of parameters, were derived in the cases of obstructive lesions of extracranial carotid arteries. The influence of these lesions and the role of anterior and posterior communicating arteries on the blood pressure at the entry of the cerebral territories were quantified and analyzed emphasizing that the responses of the system of Willis to obstructive carotid lesions are extremely varied, depending on the communicating artery anatomy. Comparison with numerical results obtained by using a non-linear model showed no physiologically significant differences. Such a model might be an essential tool for an accurate assessment of the cerebral hemodynamics in carotid diseases.

Cerebral hemodynamics in relation to patterns of collateral flow

BACKGROUND AND PURPOSE

We sought to investigate the relation between collateral flow via different pathways and hemodynamic parameters measured by dynamic susceptibility contrast-enhanced MRI in patients with severe carotid artery disease.

METHODS

Dynamic susceptibility contrast-enhanced MRI was performed in 66 patients and 33 control subjects. Patients had severe stenosis (>70%, n=12), unilateral occlusion (n=38), or bilateral occlusion (n=16) of the internal carotid artery (ICA). Cerebripetal flow and collateral flow via the circle of Willis were investigated with MR angiography. Collateral flow via the ophthalmic artery was investigated with transcranial Doppler sonography.

RESULTS

Patients with ICA stenosis had well-preserved cerebral perfusion and were in general not dependent on collateral supply. Patients with unilateral ICA occlusion had impaired cerebral perfusion. However, appearance time, peak time, and mean transit time in white matter were less increased in patients with than in patients without collateral flow via the circle of Willis (P<0.05). Furthermore, patients with collateral flow via both anterior and posterior communicating arteries had less increased regional cerebral blood volume than patients with collateral flow via the posterior communicating artery only (P<0.05). Patients with bilateral ICA occlusion had severely compromised hemodynamic status despite recruitment of collateral supply.

CONCLUSIONS

In patients with unilateral ICA occlusion, the pattern of collateral supply has significant influence on hemodynamic status. Collateral flow via the anterior communicating artery is a sign of well-preserved hemodynamic status, whereas no collateral flow via the circle of Willis or flow via only the posterior communicating artery is a sign of deteriorated cerebral perfusion.

Outcome of carotid artery occlusion is predicted by cerebrovascular reactivity

BACKGROUND AND PURPOSE

The purpose of this study was to investigate the possibility of obtaining prognostic indications in patients with internal carotid occlusion on the basis of intracranial hemodynamic status, presence of previous symptoms of cerebrovascular failure, and baseline characteristics.

METHODS

Cerebral hemodynamics were studied with transcranial Doppler ultrasonography. Cerebrovascular reactivity to apnea was calculated by means of the breath-holding index (BHI) in the middle cerebral arteries. Sixty-five patients with internal carotid artery occlusion were followed-up prospectively (median, 24 months), 23 patients were asymptomatic and 42 symptomatic (20 with transient ischemic attack and 22 with stroke).

RESULTS

During the follow-up period, 11 symptomatic patients and 1 asymptomatic patient had another ischemic event ipsilateral to carotid occlusion. Among factors considered, only lower BHI values in the middle cerebral arteries ipsilateral to carotid occlusion and older age were significantly associated with the risk of developing symptoms (P=0.002 and P=0.003, respectively; Cox regression multivariate analysis). Based on our data, a cut point of the BHI value for distinguishing between pathological and normal cerebrovascular reactivity was determined to be 0.69. All patients except one, who developed TIA or stroke during the follow-up period, had BHI values ipsilateral to carotid occlusion of <0.69.

CONCLUSIONS

These data suggest that impaired cerebrovascular reactivity is predictive for cerebral ischemic events in patients with carotid occlusion.

Cerebrovascular reactivity in carotid artery occlusion: possible implications for surgical management of selected groups of patients

OBJECTIVES

The aim of this study was to use transcranial Doppler ultrasonography to investigate cerebrovascular reactivity to hypercapnia in the middle cerebral arteries of patients with carotid occlusion with different outcomes.

PATIENTS AND METHODS

Cerebrovascular reactivity to hypercapnia was calculated with the breath-holding index (BHI). Patients with unilateral carotid occlusion were divided as follows: asymptomatic (20 patients), transient ischemic attack (TIA) (20 patients), minor (20 patients) and major stroke (14 patients). Values of BHI homolateral to the carotid occlusion were compared with those of 25 healthy subjects and 34 stroke patients without significant carotid stenosis.

RESULTS

BHI values were comparable in healthy controls, non stenotic stroke patients and asymptomatic occluded patients. BHI values of patients with symptomatic occlusion were significantly lower than those of the above-mentioned groups (P<0.0001). Moreover, the reduction of BHI was significantly associated with the extent of the neurological impairment. In fact, BHI values were significantly higher in TIA than in minor and major stroke (P<0.0001) and in minor than in major stroke patients (P<0.02). Finally, we found that a BHI value homolateral to carotid occlusion of 0.69 can be considered the cut-point for distinguishing between symptomatic and asymptomatic patients.

CONCLUSION

Prospective studies are needed to demonstrate if the presence of this threshold value may help in selecting a subset of patients with asymptomatic carotid occlusion or with transient or mild neurological deficit with the highest probability of benefiting from surgical therapy.

Predicting the effect of carotid artery occlusion during carotid endarterectomy: comparing transcranial doppler measurements and cerebral angiography

BACKGROUND AND PURPOSE

We correlated the mean transcranial Doppler blood flow velocity (FVm) during carotid endarterectomy with the functional collateral pathway(s) documented by angiography.

METHODS

Three patient groups were established: group 1 was dependent on the anterior communicating artery, group 2 on the anterior communicating artery and ipsilateral posterior communicating artery, and group 3 on the ipsilateral posterior communicating artery. Continuous middle cerebral artery FVm and electroencephalographic monitoring were performed in 45 patients during carotid endarterectomy.

RESULTS

Clamped FVm was lowest in group 3 at 17+/-9 cm/s versus 36+/-16 and 33+/-11 cm/s for groups 1 and 2 (P<0.01). FVm values in groups 1 and 2 were similar. There was significant cerebral arterial vasodilation in group 3 patients on the basis of a pulsatility index of 0.38+/-0.15. The maximum FVm after clamp release was similar among the 3 groups. Normalized blood flow velocity 1 minute before release of the clamp was increased from the minimum flow velocity after clamping only in group 1 and 2 patients.

CONCLUSIONS

The ipsilateral posterior communicating artery is a minor collateral pathway during acute carotid occlusion that contributes little to the collateral flow if there is a functional anterior communicating artery. Collateral flow through the middle cerebral artery is not recruited during occlusion in group 3 patients. The reperfusion FVm transient is independent of the primary collateral pathway. Documentation of functional collateral pathways on the basis of Doppler or angiographic examination may be advantageous in future studies since it can provide the basis for comparison among studies.

Stroke risk factors and development of collateral flow in carotid occlusive disease

BACKGROUND AND PURPOSE

Blood flow through collateral vessels compensates for reduced blood flow through stenotic or occluded extracranial carotid arteries. Previous studies have shown that extent of collateral flow influences likelihood of stroke and its outcome. Here we analyzed the relationship between stroke risk factors (hypertension, coronary artery disease, diabetes mellitus, tobacco smoking and hypercholesterolemia) and number of patent intracranial collaterals detected by transcranial Doppler ultrasonography.

SUBJECTS AND METHODS

We studied 182 patients with various degrees of angiography proven unilateral stenosis of the internal carotid artery. Contribution of the anterior and posterior communicating arteries to the perfusion of the cerebral hemisphere on the side of the stenosis or occlusion was evaluated by a series of compression tests performed during continuous insonation of the middle cerebral artery. The number of detected collateral vessels was correlated with analyzed stroke risk factors.

RESULTS

Subjects with stenosis more than 75% or occlusion of the internal carotid artery had a higher frequency of two major intracranial collateral vessels (P< or =0.01 and P< or =0.001, respectively). Hypertensive patients with stenosis more than 75% or total carotid occlusion were more likely to have only a single collateral vessel than patients without hypertension (P< or =0.01 and P< or =0.05, respectively). Other risk factors did not influence the patency of preformed collateral vessels.

CONCLUSIONS

Hypertension hindered the development of preformed intracranial collateral vessels in our patients with carotid occlusive disease.

Role of collateral flow on cerebral hemodynamics in patients with unilateral internal carotid artery occlusion

The objective of this study was to evaluate the role of collateral blood flow via the anterior and posterior communicating arteries (ACoA and PCoA) and via the ophthalmic artery (OphA) on cerebral hemodynamics, metabolism, and border zone infarcts in 57 patients with unilateral symptomatic occlusions of the internal carotid artery. Collateral flow via the ACoA and PCoA was determined with magnetic resonance angiography (MRA) and collateral flow via the OphA with transcranial Doppler (TCD). Volume flow was studied with MRA, metabolism with 1H MR spectroscopy, CO2 reactivity with TCD, and the incidence of border zone infarcts with MRI. Compared with controls, patients had deteriorated volume flow, metabolism, and CO2 reactivity. No differences were found between patients with and patients without collateral flow through the ACoA and/or PCoA, or between patients with or without collateral flow via the OphA. Patients without collateral flow via any of these collaterals had decreased volume flow in the middle cerebral artery, decreased N-acetylaspartate/choline, and increased lactate/N-acetylaspartate, compared with the other patients. Patients with symptomatic internal carotid artery occlusion have deteriorated cerebral hemodynamics and metabolism. Different collateral flow patterns via the ACoA, PCoA, or OphA have no effect on the hemodynamic and metabolic parameters, as long as one of these pathways is present.