Stable xenon CT blood flow mapping for evaluation of patients with extracranial-intracranial bypass surgery

Cerebral autoregulation, spreading depolarization, and implications for targeted therapy in brain injury and ischemia

Cerebral autoregulation is an intrinsic myogenic response of cerebral vasculature that allows for preservation of stable cerebral blood flow levels in response to changing systemic blood pressure. It is effective across a broad range of blood pressure levels through precapillary vasoconstriction and dilation. Autoregulation is difficult to directly measure and methods to indirectly ascertain cerebral autoregulation status inherently require certain assumptions. Patients with impaired cerebral autoregulation may be at risk of brain ischemia. One of the central mechanisms of ischemia in patients with metabolically compromised states is likely the triggering of spreading depolarization (SD) events and ultimately, terminal (or anoxic) depolarization. Cerebral autoregulation and SD are therefore linked when considering the risk of ischemia. In this scoping review, we will discuss the range of methods to measure cerebral autoregulation, their theoretical strengths and weaknesses, and the available clinical evidence to support their utility. We will then discuss the emerging link between impaired cerebral autoregulation and the occurrence of SD events. Such an approach offers the opportunity to better understand an individual patient's physiology and provide targeted treatments.

Evaluation of cerebrovascular reactivity in moyamoya disease using oxygen-dependent magnetic resonance imaging

Moyamoya disease (MMD) is a rare cerebrovascular disorder marked by progressive stenosis of the internal carotid arteries. Assessing cerebral hemodynamics, specifically cerebrovascular reactivity (CVR), is vital for MMD management and prognosis. In this study, fMRI was performed in a prospective cohort of 47 patients with MMD and 32 healthy controls to investigate its utility in evaluating CVR and to explore the influence of cerebral posterior circulation compensation on CVR in MMD. The regions where the CVR values of participants with MMD were lower than those of healthy controls were primarily concentrated in the frontal, parietal, and temporal lobes (p < 0.05). In certain regions mainly supplied by posterior circulation, the CVR values of compensatory-normal subgroup tended to exceed those of compensatory-poor subgroup. fMRI can detect a significant decrease in CVR values in patients with MMD compared to healthy controls. Compensation for the posterior cerebral circulation may affect cerebrovascular reactivity.

Matrix Metalloproteinase-Mediated Neuroinflammation in Vascular Cognitive Impairment of the Binswanger Type

Vascular cognitive impairment (VCI) is a heterogeneous group of diseases linked together by cerebrovascular disease. Treatment of VCI has been hindered by the lack of a coherent pathophysiological process that could provide molecular targets. Of the several forms of VCI, the small vessel disease form is both the most prevalent and generally has a progressive course. Binswanger's disease (BD) is the small vessel form of VCI that involves extensive injury to the deep white matter. Growing evidence suggests that there is disruption of the blood-brain barrier (BBB) secondary to an inflammatory state. Matrix metalloproteinases (MMPs) are increased in the brain and CSF of patients with BD, and have been shown to disrupt the BBB in animal studies, suggesting that they may be biomarkers and therapeutic targets. Multimodal biomarkers derived from clinical, neuropsychological, imaging, and biochemical data can be used to narrow the VCI population to the progressive inflammatory form that will be optimal for treatment trials. This review describes the role of the MMPs in pathophysiology and their use as biomarkers.

Quantitative lobar cerebral blood flow for outcome prediction after traumatic brain injury

The aim of this study was to examine cortical cerebral blood flow (CBF) in patients with traumatic brain injury (TBI) and determine whether lobar cortical CBF is a better predictor of long-term neurological outcome assessed by the Glasgow Outcome Scale (GOS) than global cortical CBF. Ninety-eight patients with TBI had a stable xenon computed tomography scan (Xe/CT-CBF study) performed at various time points after their initial injury. Spearman's correlation coefficients and Kruskall-Wallis' test were used to examine the relationship between patient age, emergency room Glasgow Coma Scale (GCS), Injury Severity Score, prehospital hypotension, prehospital hypoxia, mechanism of injury, type of injury, side of injury, global average CBF, lobar CBF, number of lobes with CBF below normal, and GOS (discharge, 3 and 6 months). Univariate ordinal regression was performed using these same variables and in combination with principle component analysis (PCA) to determine independent variables for multi-variate ordinal regression. Significant correlation between age, GCS, prehospital hypotension, type of injury, global average CBF, lobar CBF, number of lobes below normal CBF, and GOS was found. Individual lobar CBF was highly correlated with global CBF and the number of lobes below normal CBF. PCA found one principle component among these three CBF variables; therefore, average global CBF and number of lobes with CBF below normal were each chosen as independent variables for multiple ordinal regression, which found age, GCS, and prehospital hypotension, global average CBF, and number of lobes below normal CBF significantly associated with GOS. This study found global average CBF and lobar CBF significantly correlated with GOS at follow-up. There was, however, no individual cerebral lobe that was more predictive than any other, which puts into question the value of calculating lobar CBF versus global CBF in predicting GOS.

Symptomatic intracranial arterial disease: incidence, natural history, diagnosis, and management

Symptomatic intracranial arterial disease is associated with a high rate of recurrent ischemic events. The management of this condition is controversial, with some advocating medical therapy as a sole means of treatment and others recommending endovascular therapy in addition to best medical management. In rare cases, surgical intervention is considered. A thorough review of the available literature was performed, and treatment recommendations based on these data are provided.

Perfusion Characteristics in Chronic Cerebrovascular Insufficiency : An Anatomically and Clinically Oriented XeCT Analysis of Cerebrovascular Atherosclerotic Disease

Xenon-enhanced computed tomography (XeCT) allows quantification of hemodynamic insufficiency in the setting of cerebrovascular atherosclerotic disease (CAD). However, data regarding the relationship between hemodynamic indices [cerebral blood flow (CBF) and cerebrovascular reserve capacity (CVRC)] and normal subjects (with aging) and pathology (progression of CAD or development of stroke symptoms) are limited. In this study, we analyzed 103 consecutive patients undergoing XeCT according to age, anatomical location and disease severity. We stratified anatomically defined ROIs according to a classification system that observes the presence of proximal stenosis (class I vs. class II/III) as well as the presence of neurological symptoms (class II vs. III); CBF, CVRC and hemodynamic stress distribution were calculated. Supratentorial CBF decreases significantly with age, but not infratentorially. Cortical CVRC remains stable over time. Our classification of disease severity correlated highly significantly with a decrease in supratentorial CBF and CVRC, though CVRC is less sensitive to age-related changes. Regression analysis delineated a CVRC of 34% to discriminate between ROI classes. Age-dependent perfusion characteristics in normal vascular territories were characterized. In CAD, CVRC remains the most sensitive parameter. A simplified classification of ROIs according to disease severity correlates well with established markers for hemodynamic insufficiency. It may facilitate comparison of different pathologies such as CAD and Moyamoya disease and will be the focus of further studies.

Reduced stroke risk in patients with compromised cerebral blood flow reactivity treated with superficial temporal artery to distal middle cerebral artery bypass surgery

Extracranial-to-intracranial (EC-IC) bypass surgery for the prevention of stroke in patients with symptomatic carotid artery occlusion has nearly ended after a randomized trial showed no benefit of the procedure. Although an EC-IC bypass might benefit patients with compromised cerebrovascular hemodynamics, the randomized trial did not differentiate patients with hemodynamic from embolic etiologies. However, subsequent investigators have identified a subgroup of patients at increased stroke risk from hemodynamic compromise.

METHODS

We examined the subsequent stroke rate of 42 patients with symptomatic carotid occlusion at high risk for stroke identified as having a baseline cerebral blood flow (CBF)<45 mL/100 g/min and a >5% CBF reduction in one vascular territory after a vasodilatory challenge from 1 g of intravenous acetazolamide on stable xenon-computed tomography (CT) CBF imaging.

RESULTS

Thirty patients (group 1) treated medically were a subgroup with carotid occlusion from our long-term natural history study. During a median follow-up of 12 months, 9 patients (30%) had a new stroke within a median of 5 months. Twelve patients (group 2) had recurrent, disabling cerebral ischemic symptoms, with 8 progressing to mild fixed neurological deficits from deep white matter infarction identified on CT. All were treated with superficial temporal artery to distal middle cerebral artery (STA-MCA) bypass with restoration of cerebrovascular reserve postoperatively; none had a stroke during the 18-month minimum follow-up (P=.041). Perioperative morbidity included subendocardial infarction in one and a small, asymptomatic left frontal hemorrhage in another patient. Early postoperative and delayed xenon/CT CBF studies obtained a median of 5 months postoperatively showed maintenance of cerebrovascular reserve.

CONCLUSION

STA-MCA bypass surgery can restore cerebrovascular reserve in high-risk patients with symptomatic internal carotid artery occlusion. This was achieved with minimal perioperative complications, resulting in a subsequent reduction of stroke frequency. We suggest that the efficacy of STA-MCA bypass surgery for symptomatic carotid occlusion be re-examined prospectively using hemodynamic selection criteria.

C-Port Flex-A–assisted automated anastomosis for high-flow extracranial-intracranial bypass surgery in patients with symptomatic carotid artery occlusion: a feasibility study

Object

Preliminary experience with the C-Port Flex-A Anastomosis System (Cardica, Inc.) to enable rapid automated anastomosis has been reported in coronary artery bypass surgery. The goal of the current study was to define the feasibility and safety of this method for high-flow extracranial-intracranial (EC-IC) bypass surgery in a clinical series.

Methods

In a prospective study design, patients with symptomatic carotid artery (CA) occlusion were selected for C-Port–assisted high-flow EC-IC bypass surgery if they met the following criteria: 1) transient or moderate permanent symptoms of focal ischemia; 2) CA occlusion; 3) hemodynamic instability; and 4) had provided informed consent. Bypasses were done using a radial artery graft that was proximally anastomosed to the superficial temporal artery trunk, the cervical external, or common CA. All distal cerebral anastomoses were performed on M2 branches using the C-Port Flex-A system.

Results

Within 6 months, 10 patients were enrolled in the study. The distal automated anastomosis could be accomplished in all patients; the median temporary occlusion time was 16.6 ± 3.4 minutes. Intraoperative digital subtraction angiography (DSA) confirmed good bypass function in 9 patients, and in 1 the anastomosis was classified as fair. There was 1 major perioperative complication that consisted of the creation of a pseudoaneurysm due to a hardware problem. In all but 1 case the bypass was shown to be patent on DSA after 7 days; furthermore, in 1 patient a late occlusion developed due to vasospasm after a sylvian hemorrhage. One-week follow-up DSA revealed transient asymptomatic extracranial spasm of the donor artery and the radial artery graft in 1 case. Two patients developed a limited zone of infarction on CT scanning during the follow-up course.

Conclusions

In patients with symptomatic CA occlusion, C-Port Flex-A–assisted high-flow EC-IC bypass surgery is a technically feasible procedure. The system needs further modification to achieve a faster and safer anastomosis to enable a conclusive comparison with standard and laser-assisted methods for high-flow bypass surgery.

Cerebrovascular insufficiency as the criterion for revascularization procedures in selected patients: a correlation study of xenon contrast-enhanced CT and PWI

In order to identify patients who suffer from hemodynamic cerebral insufficiency and can benefit from cerebral revascularization procedures, xenon-CT scanning has been established to reliably measure the critical cerebrovascular reserve capacity. As a need for alternative quantification methods arises, this study aims to characterize the significance of both time-to-peak (TTP) and mean transit time (MTT) in perfusion-weighted imaging (PWI) in this particular subset of patients. Ten patients in routine preoperative work-up for cerebral revascularization were prospectively enrolled and underwent both XeCT scanning and PWI. Cerebrovascular reserve capacity (CVRC) was calculated for each region of interest (ROI, n = 504) after administration of a vasoactive stimulus. ROIs were anatomically matched with those of PWI after TTP and MTT were calculated. Highly significant negative correlation was found for TTP and CVRC for all ROIs (r = -0.3954, p < 0.0001; symptomatic ROIs: r = -0.4867, p < 0.0001). Correlation was weak for MTT and CVCR (r = -0.1287; p < 0.01). The optimum threshold for TTP to detect impaired cerebrovascular reactivity in our patient group was 4 s (specificity 90.8%, sensitivity 44.4%) for all ROIs (TTP > 4.4 s for symptomatic ROIs, specificity 88.4%, sensitivity 62.7%). An approximative equation to calculate the probability of pathological findings could be derived from the data. The positive predictive value (PPV) was 0.76 (symptomatic 0.78) with a negative predictive value (NPV) of 0.71 (symptomatic 0.78). While PWI currently is not able to replace XeCT in the direct quantification of CVRC, it may serve as a readily available follow-up tool. A TTP threshold of greater than 4 s allows to confirm a cerebrovascular compromise in a selected high-risk subgroup of patients.

Superficial temporal artery to middle cerebral artery bypass: past, present, and future

OBJECT

The aim of this study was to review the historical developments and current status of superficial temporal artery (STA) to middle cerebral artery (MCA) bypass.

METHOD

A literature review was performed to review the origins and current uses of the STA bypass procedure in neurosurgery.

RESULTS

The idea of providing additional blood supply to the brain to prevent stroke and maintain neurological function has been present in the mind of neurosurgeons for many decades. In 1967 the first STA-MCA bypass was done by M. G. Yaşargil, and an enormous step was made into the field of microneurosurgery and cerebral revascularization. During the decades that followed, this technique was used as an adjuvant or a definitive surgical treatment for occlusive disease of the extracranial and intracranial cerebral vessels, skull base tumors, aneurysms, carotid-cavernous fistulas, cerebral vasospasm, acute cerebral ischemia, and moyamoya disease. With the results of the first randomized extracranial-intracranial (EC-IC) bypass trial and the development of endovascular techniques such as angioplasty for intracranial atherosclerotic disease and cerebral vasospasm, the indications for STA-MCA bypass became limited. Neurosurgeons continued to perform EC-IC bypasses as an adjuvant to clipping of aneurysms and in the treatment of skull base tumors and moyamoya disease; the procedure is less commonly used for atherosclerotic carotid artery occlusion (CAO) with definite evidence of hemodynamic insufficiency. The evidence that patients with symptomatic CAO and "misery perfusion" have an increased stroke risk has prompted a second trial for evaluating EC-IC bypass for stroke prevention. The Carotid Occlusion Surgery Study is a new trial designed to determine whether STA-MCA bypass can reduce the incidence of stroke in these patients. New trials will also reveal the role of the STA-MCA bypass in the prevention of hemorrhages in moyamoya disease.

CONCLUSIONS

The role of STA-MCA bypass in the management of cerebrovascular disease continues to be refined and evaluated using advanced imaging techniques and by performing randomized trials for specific purposes, including symptomatic CAO.

The pathophysiology of watershed infarction in internal carotid artery disease: review of cerebral perfusion studies

BACKGROUND AND PURPOSE

In carotid disease, infarcts can occur in the cortical as well as internal watershed (WS), or both. Better understanding the pathophysiology of WS infarcts would guide treatment. Two distinct hypotheses, namely low-flow and micro-embolism, are equally supported by neuropathological and physiological studies. Here we review the evidence regarding the mechanisms for WS stroke in carotid disease and whether they differ between cortical and internal WS infarcts.

SUMMARY OF REVIEW

After a brief account of the anatomy of the WS and the cerebrovascular physiology in circumstances of low perfusion pressure, the literature concerning the mechanisms of WS infarction in carotid disease is reviewed and discussed with emphasis on imaging and ultrasound studies of the cerebral hemodynamics.

CONCLUSIONS

The evidence strongly favors a hemodynamic mechanism for internal WS infarction, especially regarding the so-called rosary-like pattern in the centrum semiovale. However, the relationships between cortical WS infarction and hemodynamic compromise appear more complicated. Thus, although severe hemodynamic compromise appears to underlie combined cortical and internal WS infarction, artery-to-artery embolism may play an important role in isolated cortical WS infarcts. Based on the high prevalence of microembolic signals documented by ultrasound in symptomatic carotid disease, a recent hypothesis postulates that embolism and hypoperfusion play a synergetic role, according to which small embolic material prone to lodge in distal field arterioles would be more likely to result in cortical micro-infarcts when chronic hypoperfusion prevails. Future studies combining imaging of brain perfusion, diffusion-weighted imaging, and ultrasound detection of microembolic signals should help resolve these issues.

Cerebral revascularization

During the last 10 years, there has been a revival of interest in cerebral revascularization procedures. Not only have significant progressions in surgical techniques been published, the use of more advanced diagnostic methods has led to a widening of the indications for cerebral bypass surgery. The purpose of this review is to outline the current techniques for extracranial-to-intracranial (EC/IC) and intracranial-to-intracranial (IC/IC) bypass surgery, as well as to identify the current indications for revascularization procedures based on the available literature. The excimer laser-assisted non-occlusive anastomosis (ELANA) technique is described in more detail because we think that this technique almost completely eliminates the risk of cerebral ischemia due to the temporary vessel occlusion which is currently used in conventional anastomosis techniques.

Effect of xenon on cerebral autoregulation in pigs

There are little data on the effect of anaesthetic concentrations of xenon on cerebral pressure autoregulation. In this study, we have investigated the effect of 79% xenon inhalation on cerebral pressure autoregulation and CO2 response in pigs. Ten pigs were randomly allocated to receive xenon 79% or halothane anaesthesia, respectively, in a crossover designed study. Halothane was used to validate the experimental set-up. Transcranial Doppler was performed to determine the mean flow velocities in the middle cerebral artery (vMCA) during defined cerebral perfusion pressures and during normo-, hyper- and hypoventilation. The results showed that the inhalation of 79% xenon preserved cerebral autoregulation during conditions of normo-, hyper- and hypoventilation and at different cerebral perfusion pressures in pigs. These results suggest that with the inhalation of xenon, in the highest concentration suitable for a safe clinical use, cerebral autoregulation is preserved.

Craniofacial resection for malignant neoplasms of the skull base: an overview

Advances in combined transcranial and transfacial (craniofacial) approaches for malignant tumors involving the anterior skull base have demonstrated improved survival. The technique allows adequate assessment of the intracranial extent of the tumor through an appropriate craniotomy. Vital structures, such as the dura, brain, and blood vessels, can be protected or resected and reconstructed safely. An en bloc excision can be accomplished. Dural defects and/or tears are satisfactorily repaired under direct vision, ensuring a watertight closure. Finally, adequate closure of the soft tissue defect is obtained, thus segregating the cranial cavity from the potentially infected nasal cavity and the nasopharynx with a resultant decrease in morbidity. Operative mortality is low, although complication rates are high. The technique is safe and continues to be improved to reduce morbidity. To evaluate the true impact of this surgical procedure on improvement in survival as well as quality of life, a multiinstitutional registry with uniform indications is indicated. With increasing experience and well-defined indications, improvement in survival (from 50% to 60%) and reduction in morbidity (from 30% to 40%) can be demonstrated through multiinstitutional, cooperative efforts.

Evaluating the effect of superficial temporal artery to middle cerebral artery bypass on pure motor function using motor activation single photon emission computed tomography

OBJECTIVE

We evaluated and analyzed the effect of superficial temporal artery to middle cerebral artery bypass for internal carotid artery occlusion on pure motor function using motor activation single photon emission computed tomography.

METHODS

Motor activation single photon emission computed tomographic (SPECT) images were obtained for nine patients who had undergone superficial temporal artery to middle cerebral artery anastomosis for symptomatic internal carotid artery occlusion. All motor activation SPECT images using the finger opposition task on the affected side were obtained before bypass surgery and at 1 week, 1 month, and 3 months after bypass surgery. The results of motor activation single photon emission computed tomography were expressed as negative or positive.

RESULTS

Before bypass surgery, the resting SPECT images revealed reduction of cerebral blood flow (CBF) on the affected side in all nine patients. The results of motor activation single photon emission computed tomography in three patients were positive. One week after bypass surgery, the results of the resting and motor activation CBF studies did not demonstrate any marked changes. One month after bypass surgery, the resting CBF increased in four patients. The results obtained for two of the patients revealed preoperative positive motor activation. The results of motor activation single photon emission computed tomography obtained for five patients were positive. Three months after bypass surgery, eight patients experienced improvement in the resting CBF, and the results of motor activation single photon emission computed tomography obtained for seven patients were positive. Among these, the results of preoperative motor activation single photon emission tomography obtained for four patients were negative.

CONCLUSION

Superficial temporal artery to middle cerebral artery bypass is useful not only for resting CBF but also for pure motor function based on motor activation SPECT images. From the preoperative motor activation study, it was concluded that patients with preoperative positive motor activation could attain the effect of bypass earlier than patients with preoperative negative motor activation.

Physiological diagnosis and surgical treatment of recurrent limb shaking: case report

OBJECTIVE AND IMPORTANCE

Although recurrent limb shaking has been observed in patients with carotid occlusion, its cause, method of diagnosis, and definitive treatment have yet to be fully elucidated. This report examines the cerebrovascular physiology of a patient with recurrent limb shaking by means of xenon-enhanced computed tomographic (XeCT) scanning. By measuring cerebral blood flow (CBF) and cerebrovascular reserve capacity, we were able to confirm both the clinical diagnosis and the response to treatment on physiological grounds.

CLINICAL PRESENTATION

The patient is a 49-year-old man who presented with frequent brief attacks of left arm and leg shaking that occurred at standing or coughing. After cervical radiation therapy for a laryngeal carcinoma, he was found to have bilateral carotid occlusion with minimal collateral development. XeCT scans revealed borderline ischemic perfusion and lack of cerebrovascular reserve in response to an acetazolamide vasodilatory challenge.

INTERVENTION

The patient underwent a right superficial temporal artery to middle cerebral artery bypass to augment cerebral perfusion.

CONCLUSION

After the procedure, the patient's limb shaking attacks ceased. The postoperative XeCT scan showed improved CBF and a return of cerebrovascular reserve capacity. Recurrent limb shaking is a manifestation of decreased CBF. Quantitative XeCT CBF studies coupled with vasodilatory challenge is an important way to assess patients with cerebrovascular disorders and thus identify individuals who will benefit from cerebral revascularization.

Dynamics of cerebral blood flow and metabolism in patients with cranioplasty as evaluated by 133Xe CT and 31P magnetic resonance spectroscopy

OBJECTIVE

Prolonged improvement in neurological and mental disorders has been seen after only cranioplasty in patients initially treated with external decompression for high intracranial pressure. The objective was to evaluate, using 133Xe CT and 31P magnetic resonance spectroscopy (MRS), how restoring the bone itself can influence cerebral blood flow and cerebral energy metabolism after high intracranial pressure is attenuated.

METHODS

Seven patients (45-65 years old) who had undergone external decompression to prevent uncontrollable intracranial hypertension after acute subarachnoid haemorrhage were evaluated. Cerebral blood flow and metabolic changes were evaluated before and after cranioplasty.

RESULTS

The ratio of phosphocreatine to inorganic phosphate (PCr/Pi), which is a sensitive index of cerebral energy depletion, was calculated and beta-ATP was measured. The cerebral blood flow value in the thalamus was normalised, from 44 (SD 9) to 56 (SD 8) ml/100 g/min (P < 0.01) and the value in the hemisphere increased from 26 (SD 3) to 29 (SD 4) ml/100 g/min on the side with the bone defect. The PCr/Pi ratio improved greatly from 2.53 (SD 0.45) to 3.01 (SD 0.24) (P < 0.01). On the normal side, the values of cerebral blood flow and PCr/Pi increased significantly (P < 0.01) after cranioplasty, possibly due to transneural suppression. The pH of brain tissue was unchanged bilaterally after cranioplasty.

CONCLUSION

Cranioplasty should be carried out as soon as oedema has disappeared, because a bone defect itself may decrease cerebral blood flow and disturb energy metabolism.

Acetazolamide produced blood flow velocity changes measured by laser Doppler in gerbils with reduced CBF

The effect of acetazolamide on the cerebral blood flow was studied in gerbils with unilateral carotid ligation. According to the effect of ligation the animals were divided into three groups: first group-the reduction more than 70%, second-CBF reduction 30-70% and the third group-CBF reduction less than 30%. The effect of acetazolamide administration was closely related to the effect of carotid ligation. More reduction of CBF was produced by carotid ligation, less increase of CBF after acetazolamide injection was noticed. The acetazolamide vascular reserve test was found a sensitive and useful method for detecting even modest reduction of vascular reserve in animals with slight - less than 30% CBF decrease following carotid ligation.

Middle cerebral artery endarterectomy: experience with two cases

BACKGROUND

Atherosclerotic stenosis of the middle cerebral artery (MCA) is uncommon and long-term prognosis is not well defined. Methods of treating stenosis of the MCA range from the administration of anticoagulants to endarterectomy.

METHODS

We present two cases of patients with focal symptomatic stenosis of the MCA with evidence of focally decreased cerebral blood flow and compromise of cerebral blood flow reserves on xenon-enhanced computed tomography (Xe CT) scanning. Endarterectomies were performed after unsuccessful anticoagulation therapy.

RESULTS

Both patients underwent successful endarterectomies of the MCA. Improvement in cerebral blood flow postoperatively was documented for both patients. At last follow-up neither patient had demonstrated any additional ischemic episodes.

CONCLUSIONS

Atherosclerotic stenosis of the MCA may be responsible for distal emboli and compromised hemodynamics, and endarterectomy of this vessel may provide definitive therapy.

Effects of superficial temporal to middle cerebral artery bypass for ischaemic retinopathy due to internal carotid artery occlusion/stenosis

The effects of superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis for retinopathy is discussed and analysed in 19 cases of occlusive internal carotid artery disease (4 with stenosis and 15 with occlusion) according to Doppler sonography (DS) of the retinal artery, optic fundi and visual impairment symptoms. Preoperatively, all cases showed abnormal DS findings (stenosis patterns in 2 cases and the reversed flow patterns in 17 cases). All cases showed ischaemic changes of the optic fundi. Visual symptoms were amaurosis fugax in 2 cases, decline of visual acuity in 13 cases and both in 4 cases. At one month after the bypass, two stenosis pattern cases showed almost normal DS findings. In the 17 reversed flow pattern cases, 13 cases had a marked improvement of the reversed flow. The ischaemic changes of the optic fundi were ameliorated in 12 cases. In the follow-up stage, greater improvement in the DS findings and the optic fundi could be seen in all cases. In all cases worsening of the visual acuity was prevented, and in some cases the decreased visual acuity improved. The above improvements correlated well with the improvement of DS findings. It is believed that this procedure should be performed to prevent and improve ischaemic retinopathy caused by ischaemic ICA lesion.

Increased stroke risk predicted by compromised cerebral blood flow reactivity

The authors sought to determine risk for stroke in individuals with symptomatic carotid stenosis or occlusion based upon an assessment of cerebral blood flow (CBF) reserves. Vascular reserve was assessed by two consecutive xenon/computerized tomography (Xe/CT) CBF studies with intravenous acetazolamide introduced 20 minutes prior to the second study. Patients were assigned to one of two vasoreactivity groups. Group 2 included individuals who experienced a CBF reduction of more than 5% in at least one vascular territory and had a baseline flow of 45 cc/100 gm/min or less. Group 1 included all other individuals. Any territory with volume loss on CT of more than 50% was eliminated from analysis. Sixty-eight individuals were followed at 6-month intervals for a mean of 24 months. In Group 1 two strokes were observed contralateral to the side with lowest reserve, for a stroke incidence of 4.4%; in Group 2 eight strokes were observed ipsilateral to the side with lowest reserve, for a stroke incidence of 36%. The latter group had a 12.6 times greater chance of stroke (p = 0.0007). History of stroke, history of transient ischemic attacks, baseline CBF, and degree of stenosis were not associated with an increased stroke rate. In this study, significantly compromised vascular reserves accompanied by relatively low initial flow identified individuals who subsequently demonstrated a significantly increased rate of ipsilateral stroke.

Hemodynamic and electrophysiological evaluation following extracranial/intracranial bypass surgery

We examined 50 patients with an extracranial/intracranial bypass using transcranial Doppler blood flow mapping, somatosensory evoked potentials, and computer-assisted EEG analysis. The investigation was supplemented by temporary compression of the extracranial supplying vessel. Transcranial Doppler sonography revealed in addition to 4 patients with nonpatent anastomoses, a bypass-mediated retrograde flow in the ipsilateral middle cerebral artery beyond a depth of 40 mm in the majority of patients. In 9 patients, retrograde flow could be demonstrated in the whole proximal (M1) MCA segment. The precommunicating segment of the anterior cerebral artery (A1) could be reliably insonated in all but 5 patients. Bypass-compression dependent alterations in the SSEP and in EEG analysis were only observed in a small number of patients. Transcranial Doppler sonography, with the aid of the flow mapping system, appears therefore, to be a reliable and repeatedly performable noninvasive technique for the assessment of intracranial hemodynamics following bypass surgery.

Effect of 33% xenon inhalation on whole-brain blood flow and metabolism in awake and fentanyl-anesthetized monkeys

BACKGROUND AND PURPOSE

Despite the documented diagnostic value of local cerebral blood flow maps by xenon-enhanced computed tomography, reports of cerebral blood flow activation by inhaled 33% Xe raised concerns about the method's safety and accuracy. We evaluated the effect of 33% Xe inhalation on cerebral blood flow and cerebral metabolic rates for oxygen and glucose in four awake and six fentanyl-anesthetized rhesus monkeys.

METHODS

Platinum microelectrodes and catheters in the torcular Herophili were used to measure cerebral blood flow by hydrogen clearance, and oxygen and glucose concentrations. Cerebral variables were measured after 5 and 35 minutes of exposure to room air followed randomly by 67% O2 in 33% N2 or Xe. Five- and 35-minute measurements were combined because the duration of exposure had no effect.

RESULTS

In awake monkeys, 33% Xe compared with 33% N2 reduced (p less than 0.05) cerebral blood flow from 75 +/- 12 to 66 +/- 9 (mean +/- SD) ml.100 g-1.min-1 and oxygen consumption from 6.1 +/- 0.7 to 5.1 +/- 0.6 ml.100 g-1.min-1. In fentanyl-anesthetized monkeys, cerebral variables during 33% N2 versus 33% Xe were cerebral blood flow, 84 +/- 26 versus 79 +/- 23 ml.100 g-1.min-1; oxygen consumption, 5.0 +/- 0.7 versus 4.9 +/- 0.5 ml.100 g-1.min-1; and glucose consumption, 8.4 +/- 1.9 versus 7.9 +/- 2.0 mg.100 g-1.min-1.

CONCLUSIONS

In awake monkeys, 33% Xe reduced rather than activated cerebral blood flow and oxygen consumption by 12% and 16%, respectively; it had no effect in fentanyl-anesthetized monkeys.

CBF measured by Xe-CT: approach to analysis and normal values

Normal reference values and a practical approach to CBF analysis are needed for routine clinical analysis and interpretation of xenon-enhanced computed tomography (CT) CBF studies. We measured CBF in 67 normal individuals with the GE 9800 CT scanner adapted for CBF imaging with stable Xe. CBF values for vascular territories were systematically analyzed using the clustering of contiguous 2-cm circular regions of interest (ROIs) placed within the cortical mantle and basal ganglia. Mixed cortical flows averaged 51 +/- 10ml.100g-1.min-1. High and low flow compartments, sampled by placing 5-mm circular ROIs in regions containing the highest and lowest flow values in each hemisphere, averaged 84 +/- 14 and 20 +/- 5 ml.100 g-1.min-1, respectively. Mixed cortical flow values as well as values within the high flow compartment demonstrated significant decline with age; however, there were no significant age-related changes in the low flow compartment. The clustering of systematically placed cortical and subcortical ROIs has provided a normative data base for Xe-CT CBF and a flexible and uncomplicated method for the analysis of CBF maps generated by Xe-enhanced CT.

A simplified method for measuring cerebral blood flow with xenon-enhanced computed tomography

The measurement of cerebral blood flow using the xenon-enhanced computed tomography (XECT) technique requires that the build-up of xenon in both brain tissue and end-tidal expired air be determined as a function of time. Monitoring of the former is carried out using CT scanning and the latter, most often, using a thermoconductivity analyser or mass spectrometer. This paper examines the possibility of greatly simplifying the XECT technique by eliminating the need for either thermoconductivity analyser or mass spectrometer. In the proposed approach, the patient's expired air is channelled through the scan field using a flexible plastic tube and sampled by the CT scanner in conjunction with the build-up of xenon in brain tissue. Phantom measurements have demonstrated the ability of the CT scanner to detect variations in the xenon concentration in expired air while computer simulations have shown that errors arising as a result of the proposed methodology are small compared to other inherent sources in the XECT technique.

Xenon-enhanced computed tomography compared with [14C]iodoantipyrine for normal and low cerebral blood flow states in baboons

The correlation between the acute, invasive diffusible [14C]iodoantipyrine technique for cerebral blood flow and the noninvasive xenon-enhanced computed tomographic method has been assessed by simultaneous measurements in the baboon. Blood flows in small tissue volumes (about 0.125 cm3) were directly compared in normal and low flow states. These studies demonstrate a statistically significant association between the two methods (p less than 0.001). Similar correlations were obtained by both the Kendall (tau) and the Spearman (r) methods (r = 0.67 to 0.92, n greater than or equal to 19 for each study). The problems and limitations of such correlations are discussed.

Stable xenon versus radiolabeled microsphere cerebral blood flow measurements in baboons

Regional cerebral blood flow was simultaneously determined using the stable xenon computed tomographic and the radioactive microsphere techniques over a wide range of blood flow rates (less than 10-greater than 300 ml/100 g/min) in 12 baboons under conditions of normocapnia, hypocapnia, and hypercapnia. A total of 31 pairs of determinations were made. After anesthetic and surgical preparation of the baboons, cerebral blood flow was repeatedly determined using the stable xenon technique during saturation with 50% xenon in oxygen. Concurrently, cerebral blood flow was determined before and during xenon administration using 15-microns microspheres. In Group 1 (n = 7), xenon and microsphere determinations were made repeatedly during normocapnia. In Group 2 (n = 5), cerebral blood flow was determined using both techniques in each baboon during hypocapnia (PaCO2 = 20 mm Hg), normocapnia (PaCO2 = 40 mm Hg), and hypercapnia (PaCO2 = 60 mm Hg). Xenon and microsphere values in Group 1 were significantly correlated (r = 0.69, p less than 0.01). In Group 2, values from both techniques also correlated closely across all levels of PaCO2 (r = 0.92, p less than 0.001). No significant differences existed between the slopes or y intercepts of the regression lines for either group and the line of identity. Our data indicate that the stable xenon technique yields cerebral blood flow values that correlate well with values determined using radioactive microspheres across a wide range of cerebral blood flow rates.

Superficial temporal-middle cerebral artery bypass: clinical pre- and postoperative angiographic correlation

Between 1974 and 1982, an anastomosis between a pedicle of the superficial temporal artery (STA) and a cortical branch of the middle cerebral artery (MCA) was performed in 163 carotid systems in 157 patients for internal carotid artery occlusion in whom postoperative angiograms were available for analysis. The angiographic opacification of the arterial system was correlated with the patient's preoperative neurological function and stroke in the follow-up period. From this analysis, the following observations were made: 1) 96% of bypasses were patent; 2) 80% of bypasses achieved a high or medium MCA filling score; 3) there was hypertrophy of the STA in 70% of the cases; 4) greater bypass filling occurred in hemispheres with nonvisualized preoperative collateral circulation than in those with readily visualized collateral flow; 5) a meaningful correlation between angiographically assessed postoperative bypass function and stroke rate was not possible because only four patients suffered an ipsilateral hemispheric stroke in the 8-year follow-up period; and 6) patients who were neurologically unstable before the procedure were at greatest risk for a stroke in the follow-up period. It is apparent that objective analysis of the effectiveness of an STA-MCA bypass, or any other form of extracranial bypass, must await the development of new diagnostic studies in which high-resolution three-dimensional quantification of cerebral blood flow is possible. These studies will necessarily be correlated with preoperative and follow-up clinical data.

Improvement of global cerebral blood flow after STA-MCA bypass in a patient with bilateral occlusion of the internal carotid artery: effect of surgery or natural course?

A xenon-CT examination was performed on a patient who had received a STA-MCA bypass. Evaluation of cerebral blood flow (CBF) pre- and postoperatively shows a post-operative increase of about 60%. During manual compression of STA, a decrease of 20% was observed so that one third of the total CBF increase could be attributed to anastomosis. The remaining two thirds may originate from the natural collateral circulation.

Critique of the extracranial-intracranial bypass study

The potential benefit of extracranial-intracranial anastomosis was evaluated by a multicenter international cooperative study headed by the group in London, Ontario, Canada. The final conclusion of the study was that the extracranial-intracranial anastomosis did not provide any benefit over the treatment with aspirin. Several objections and shortcomings have been identified in this study. In our evaluation it cannot be concluded that EC-IC bypass surgery is not effective in reducing stroke in all patient populations.

Failure of extracranial-intracranial arterial bypass to reduce the risk of ischemic stroke. Results of an international randomized trial

To determine whether bypass surgery would benefit patients with symptomatic atherosclerotic disease of the internal carotid artery, we studied 1377 patients with recent hemisphere strokes, retinal infarction, or transient ischemic attacks who had atherosclerotic narrowing or occlusion of the ipsilateral internal carotid or middle cerebral artery. Of these, 714 were randomly assigned to the best medical care, and 663 to the same regimen with the addition of bypass surgery joining the superficial temporal artery and the middle cerebral artery. The patients were followed for an average of 55.8 months. Thirty-day surgical mortality and major stroke morbidity rates were 0.6 and 2.5 per cent, respectively. The postoperative bypass patency rate was 96 per cent. Nonfatal and fatal stroke occurred both more frequently and earlier in the patients operated on. Secondary survival analyses comparing the two groups for major strokes and all deaths, for all strokes and all deaths, and for ipsilateral ischemic strokes demonstrated a similar lack of benefit from surgery. Separate analyses in patients with different angiographic lesions did not identify a subgroup with any benefit from surgery. Two important subgroups of patients fared substantially worse in the surgical group: those with severe middle-cerebral-artery stenosis (n = 109, Mantel-Haenszel chi-square = 4.74), and those with persistence of ischemic symptoms after an internal-carotid-artery occlusion had been demonstrated (n = 287, chi-square = 4.04). This study thus failed to confirm the hypothesis that extracranial-intracranial anastomosis is effective in preventing cerebral ischemia in patients with atherosclerotic arterial disease in the carotid and middle cerebral arteries.