Cerebral angiographic risk in mild cerebrovascular disease

Results of parenchymal and angiographic magnetic resonance imaging and neuropsychological testing of children after stroke as neonates

We describe the long-term follow up of infants after neonatal stroke of the middle cerebral artery (MCA). Stroke was diagnosed by CT scan in eight full-term neonates. Three dimensional (volume) magnetic resonance angiography (MRA) is a noninvasive technique that images the arterial vessels without contrast agents. All patients, aged from 1.5 to 8.4 years, were investigated by MRI and MRA and by neuropsychological tests. Cognitive development was investigated by intelligence tests, tests of visual perception, motor and language development. Out of the eight patients, seven had a retarded mental and motor development, and 50% of the children were treated for epilepsy. Seven patients had a spastic hemiparesis. Seven out of eight children showed major cognitive deficits. In all patients, MRI revealed clear parenchymal defects with variable distribution patterns. MRA studies showed abnormalities corresponding to the expected vascular distribution. Children with complications at delivery, with seizures, and an interruption of the main stem of MCA as demonstrated on MRA had the least favourable long-term follow up prognosis with severe cognitive delays.

Variables affecting the accuracy of stereotactic localization using computerized tomography

Stereotactic localization using computerized tomography (CT) is increasingly employed to guide neurosurgical procedures in crucial areas of the brain such as the brain stem. This technique allows the surgeon to resect a lesion in its entirety while sparing critical areas of the brain. Thus, the parameters used for scanning should be selected for maximum accuracy. While the small pixel size of CT scanners suggests a high degree of precision in localization, there have been few systematic studies of this accuracy. The authors have studied the amount of error in localization created by variables such as CT scan thickness, interscan spacing, size of lesion, and method of computation when using the Brown-Roberts-Wells (BRW) stereotactic system. Over 1000 CT scans were made of a phantom composed of spheres of differing diameter and location. The CT slice thickness was varied from 1.5 to 5.0 mm, and interscan spacing was varied from 0.5 to 3.0 mm. The coordinates of the center of the spheres were calculated independently using the laptop computer supplied with the unit and also by a stereotactic computer which automatically calculates the center of the fiducials. The actual BRW coordinates of the sphere center were obtained using the phantom base and were then compared to the computer-calculated coordinates to determine error in localization. Variables with a significant effect on error included the scan thickness, interscan spacing, and sphere size. The mean error decreased 23% as the scan thickness decreased from 5.0 to 1.5 mm and 45% as the interscan spacing decreased from 3.0 to 0.5 mm. Mean error was greatest for the smallest sphere sizes. The two computational methods did not differ in error. This study suggests that, for critical areas of the brain or for small lesions, a scan thickness of 1.5 mm and interscan spacing of 0.5 mm should be employed.

Complications of intraarterial digital subtraction angiography in patients investigated for cerebral vascular disease

395 patients (236 males, mean age 55.6 years: 159 females, mean age 52.2 years) with suspected transient ischaemic attacks or previous strokes underwent intraarterial digital subtraction angiography (IADSA) over a 3-year period ending in March 1991. All procedures were performed via the femoral approach and the majority consisted of arch studies followed by selective catheterization. 253 (64.1%) of the patients had extracranial vascular disease confirmed at angiography. A retrospective analysis of the patients' records was made to extract all possible complications. Complications were defined as any untoward symptoms or signs occurring within 48 h and which could have been related to the angiogram. Neurological complications occurred in 15 (3.89%) patients. 10 (2.5%) patients had transient complications which resolved completely within 24 h. In three (0.8%) patients the neurological deficit was reversible, recovering fully within 6 days. Two (0.52%) patients were left with residual disability from stroke at 10 days. The permanent neurological complication rate is in the lower range of the rates recorded in previous conventional angiographic studies. We conclude that IADSA is a relatively safe and reliable form of investigation in patients with suspected cerebral vascular disease.

Relative characteristics of MR angiography and competing vascular imaging modalities

This article reviews the general characteristics of several vascular imaging modalities with the purpose of identifying the distinguishing features of magnetic resonance (MR) angiography. Brief discussions of conventional x-ray film angiography, intravenous and intraarterial digital subtraction angiography (DSA), duplex and color Doppler flow ultrasound (US), computed tomographic (CT) angiography, transesophageal and intravascular US, angioscopy, and MR angiography are presented. The advantages and disadvantages of each are discussed. The general attributes and image quality features of MR angiography, intraarterial DSA, CT angiography, and US are compared. It is concluded that no single imaging modality will presently suffice for all purposes. Because of its noninvasiveness, rapidly improving image quality, and ability to directly provide velocity information, MR angiography is likely to play a role in an increasing number of clinical applications.

Complications of cerebral angiography in patients with symptomatic carotid territory ischaemia screened by carotid ultrasound

After nearly 40 years, carotid endarterectomy has been shown to be of benefit to patients with symptomatic carotid territory ischaemia and greater than 70% stenosis of the relevant internal carotid artery. Cerebral angiography is performed before surgery and is not without risk. These risks must be added to those of surgery before recommending the procedure to patients. The study evaluated the local, systemic and neurological complications following digital subtraction angiography with selective catheterisation of the carotid arteries in 200 patients presenting to a cerebrovascular clinic for assessment of cerebral ischaemia. All patients had carotid ultrasound screening before angiography to screen out those with normal arteries or mild disease (less than 30% stenosis of symptomatic internal carotid artery). Complications occurred in 28 patients. There were six (3%) local, two (1%) systemic and 20 (10%) neurological complications. Seventeen neurological complications occurred within 24 hours and there were three late complications (24-72 hours). Neurological complications occurred more frequently when angiography was performed by a trainee rather than a consultant neuroradiologist (p < 0.01). The neurological complications were transient (resolved within 24 hours) in 10/200 (5%), reversible (resolved within seven days) in two (1%) and permanent in 8/200 (4%). Two patients died after a stroke and two other patients suffered a disabling stroke. At 24 hours post angiography the permanent (persisting beyond seven days) neurological complication rate was 2.5%. The incidence of total neurological complications and post angiographic strokes was higher in patients with greater than 90% stenosis of the symptomatic internal carotid artery (p < 0.001). The increased use of non-invasive Doppler duplex screening will reduced the absolute number of patients put at risk of angiography, yet the rate of post angiographic complications is likely to increase as patients with severe stenosis of the symptomatic internal carotid artery are probably most at risk of complications and have most to gain from carotid endarterectomy.

Are both color-flow duplex scanning and cerebral arteriography required prior to carotid endarterectomy?

In an attempt to eliminate the morbidity, mortality, and cost associated with arteriography, surgeons are relying increasingly on duplex scanning of the extracranial arteries as the primary preoperative evaluation prior to carotid endarterectomy (CEA). This study was initiated to evaluate the need for cerebral arteriography in the preoperative evaluation of patients for CEA. One hundred five patients undergoing 114 CEA procedures are included in a retrospective review to determine whether the addition of cerebral arteriography changed the operative management of these patients. In 58 of 105 patients (55%), color-flow duplex scanning and cerebral arteriography were performed in the workup prior to CEA. In four patients a discrepancy was found between the duplex results and the arteriogram, leading to a change in the operative approach in two. The remaining 47 patients (45%) underwent color-flow duplex scanning as the definitive preoperative study; the surgical management was altered because of the operative findings in one patient. Although color-flow duplex scanning does not provide absolute concordance with cerebral arteriography, in most instances it can be used as the definitive preoperative study prior to CEA. We define the indications for cerebral arteriography in patients undergoing CEA.

Magnetic resonance angiography of vascular lesions causing neuro-ophthalmic deficits

Magnetic resonance angiography (MRA) is a noninvasive, rapidly evolving technique for imaging the intra- and extracranial carotid and vertebrobasilar circulations. It may in some circumstances obviate conventional angiography and the accompanying risks associated with catheterization and contrast injection. MRA exploits the different physical properties between moving protons and stationary tissue to yield flow sensitive data in the form of anatomic images or velocity and flow measurements. Since patients with various vascular disorders may present exclusively with ophthalmologic signs and symptoms, it is expected that MRA will become more frequently utilized by ophthalmologists. The exact role of MRA in the workup of vascular disorders remains to be more precisely defined, pending the performance of additional well-controlled standardized studies. At present, MRA is utilized to complement the conventional spin-echo studies of patients with arterial and venous occlusion, vascular malformations, intracranial aneurysms, and neoplastic vascular invasion. With further refinements, it is expected that MRA will become a standard diagnostic tool for the evaluation of patients with vascular disorders.

Microscopic air embolism during cerebral angiography and strategies for its avoidance

Cerebral angiography is associated with a risk of neurological complications and air embolism may contribute towards this risk. To test this hypothesis, transcranial doppler ultrasonography was used to monitor the presence of air emboli in the middle cerebral arteries of 7 patients undergoing cerebral angiography. Doppler signals consistent with numerous air emboli were noted during each injection of radiographic contrast. This phenomenon was studied further in sheep. Radiographic contrast medium was injected into the carotid artery while a major carotid branch was insonated transorbitally. Embolic signals similar to those seen in patients were noted. Air was introduced at two points. First, at the time of drawing up the contrast into the syringe, especially with more viscous media. Standing the media before injection resulted in a highly significant reduction of air embolism, reducing the total mean duration of emboli from 1.32 (SD 0.60) s after immediate injection to 0.04 (0.05) s after ten minutes standing for iohexol 340 mg/mL (p < 0.001). Second, air was introduced at the time of injection, possibly by the formation of cavitation bubbles under pressure. This occurred most prominently with the less viscous contrast media and with saline, and was significantly reduced by slow injection (mean duration of emboli for saline 2.85 [2.43] s with fast injection compared with 0.32 [0.37] s with slow injection, p = 0.004). Air embolism may contribute towards neurological dysfunction after angiography. Measures should be taken to reduce this by allowing contrast media to stand prior to injection, and by flushing catheters with saline injected slowly.

Surgical decisions on the basis of magnetic resonance angiography of the carotid arteries

The recent demonstration of the efficacy of carotid endarterectomy in certain patients emphasizes the advantages of having a noninvasive, accurate means of evaluating the carotid arteries. Advances in magnetic resonance (MR) angiography now allow accurate depiction of the carotid arteries that may be adequate for surgical planning in many cases. This report examines the accuracy of MR angiography compared with that of conventional angiography in symptomatic patients undergoing carotid endarterectomy and compares them with surgical findings. Twenty-one carotid arteries in 20 patients were treated surgically for severe stenosis or occlusion. Preoperatively, all patients had both MR and conventional angiograms, which were interpreted on a five-grade scale by two independent neuroradiologists who were unaware of the patient's clinical history. The two studies were highly correlated, particularly in the case of severe stenosis and occlusion. There were no false-negative MR studies that missed surgically significant lesions. In two cases, MR angiography overestimated the stenosis by one grade. On MR angiography, surgically significant stenosis appears as focal areas of signal intensity loss at the level of stenosis with reappearance of the signal distally. If the distal signal intensity does not reappear, the artery is likely to be occluded. In symptomatic patients, MR angiograms that demonstrate a flow-void gap with distal reappearance at a site consistent with the symptoms may be adequate as the sole preoperative study. Three patients who underwent carotid endarterectomy on this basis are presented. The factors that contribute to artifactual and overestimated stenosis are reviewed.

Natural history of patients with chronic occlusion of the internal carotid artery

Although 3% of the elderly population may have asymptomatic unilateral internal carotid artery occlusion (ICAO), between 10% and 20% of patients with initial stroke in the carotid territory have appropriate ipsilateral extracranial ICAO. In the latter instance, it is often difficult to establish whether ICAO is (a) an acute thrombotic process on an underlying atheromatous stenosis; (b) an acute embolic ICAO (from heart or aorta); or (c) an old ICAO that was previously asymptomatic. Intracranial studies show that the first stroke ipsilateral to ICAO is usually associated with occlusions distal to ICAO, which suggest artery-to-artery embolism. On the other hand, the follow-up of stroke patients with ICAO shows that delayed cerebral infarction distal to the established ICAO often involves watershed areas and may correspond to hemodynamic disturbances. Because the international extracranial/intracranial arterial bypass study did not show any surgical benefit, current management is mainly directed to stabilization of associated causes of hemodynamic failure (hypotension, bradycardia, etc.). Attempts to find subgroups that may benefit from bypass surgery are still ongoing. However, the prognosis of these patients is negatively influenced by a particularly high risk of cardiac death.

Prevention of ischemic stroke: the role of carotid endarterectomy in symptomatic patients

Carotid endarterectomy (CE) has recently been proved to be beneficial in symptomatic patients with severe (70-99%) appropriate carotid stenosis. After discussing the historical evolution of CE as a possible preventive treatment of ischemic stroke, we review the results of North American and European trials in order to give practical information for the management of cerebrovascular patients.

Cost-effective investigation of patients with suspected transient ischaemic attacks

Images

Pediatric magnetic resonance angiography: assessment of stroke

Thirty-one (59.6%) of 52 magnetic resonance angiographic (MRA) studies performed on pediatric patients were for evaluation of strokes. Thirteen of the 31 patients (41.9%) of MRA studies were positive for either vascular occlusion or congenital vascular malformation (arteriovenous, venous, or aneurysm). Results indicate that MRA is a valuable noninvasive diagnostic tool that can be routinely performed as part of the initial magnetic resonance evaluation, often thereby avoiding the need for conventional angiography in occlusive vascular disease, and permitting the performance of conventional angiography, in the case of vascular malformations, later when the patient is stable.

Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis

BACKGROUND

Without strong evidence of benefit, the use of carotid endarterectomy for prophylaxis against stroke rose dramatically until the mid-1980s, then declined. Our investigation sought to determine whether carotid endarterectomy reduces the risk of stroke among patients with a recent adverse cerebrovascular event and ipsilateral carotid stenosis.

METHODS

We conducted a randomized trial at 50 clinical centers throughout the United States and Canada, in patients in two predetermined strata based on the severity of carotid stenosis--30 to 69 percent and 70 to 99 percent. We report here the results in the 659 patients in the latter stratum, who had had a hemispheric or retinal transient ischemic attack or a nondisabling stroke within the 120 days before entry and had stenosis of 70 to 99 percent in the symptomatic carotid artery. All patients received optimal medical care, including antiplatelet therapy. Those assigned to surgical treatment underwent carotid endarterectomy performed by neurosurgeons or vascular surgeons. All patients were examined by neurologists 1, 3, 6, 9, and 12 months after entry and then every 4 months. End points were assessed by blinded, independent case review. No patient was lost to follow-up.

RESULTS

Life-table estimates of the cumulative risk of any ipsilateral stroke at two years were 26 percent in the 331 medical patients and 9 percent in the 328 surgical patients--an absolute risk reduction (+/- SE) 17 +/- 3.5 percent (P less than 0.001). For a major or fatal ipsilateral stroke, the corresponding estimates were 13.1 percent and 2.5 percent--an absolute risk reduction of 10.6 +/- 2.6 percent (P less than 0.001). Carotid endarterectomy was still found to be beneficial when all strokes and deaths were included in the analysis (P less than 0.001).

CONCLUSIONS

Carotid endarterectomy is highly beneficial to patients with recent hemispheric and retinal transient ischemic attacks or nondisabling strokes and ipsilateral high-grade stenosis (70 to 99 percent) of the internal carotid artery.

Duplex scanning alone before carotid endarterectomy: a 5-year experience

The role of duplex scanning and arteriography as a means of assessing patients for carotid endarterectomy has been reviewed for the period 1984 to 1988 when 98 carotid endarterectomies were performed. Of these 44 were selected for surgery on the basis of duplex assessment alone, 48 after carotid angiography and duplex scanning and six after angiography alone. No difference between the groups of patients was observed for either perioperative or follow-up complication rates, although all late deaths occurred in patients who had been examined by angiography. By the end of the study period angiography was requested for less than 30% of all patients undergoing carotid endarterectomy. It is argued that the change in our practice is safe provided that certain criteria are met. These include angiography in cases of suspected aortic arch or proximal vessel disease and in those symptomatic patients with a duplex diagnosis of complete occlusion.

Cerebrovascular abnormalities in pediatric stroke: assessment using parenchymal and angiographic magnetic resonance imaging

Three-dimensional (volume) magnetic resonance angiography is a noninvasive technique that images the intracranial and cervical arterial vasculature without contrast agents. Twenty-four children with strokes had combined parenchymal magnetic resonance imaging and magnetic resonance angiography 1 day to 4 years after acute presentation. Eight had had prior intra-arterial angiography. Eighteen magnetic resonance angiographic studies showed arterial stenosis or occlusion in the vascular distribution of magnetic resonance image-defined brain infarction and, in 7 children, in the same location as previously defined abnormalities on intra-arterial angiography. One child had a normal intra-arterial angiogram and magnetic resonance angiogram. The other 5 children with normal magnetic resonance angiographic studies included 3 with presumed embolic disease, 1 with meningitis, and 1 with Crohn's disease-related vasculitis. Collateral flow patterns could be determined in 4 children. Artifact presenting as filling defects in vessels was present in 10 studies, but did not interfere with interpretation of 8 studies. Combined magnetic resonance imaging/magnetic resonance angiography provides a screening technique to evaluate noninvasively brain parenchyma and vasculature in children with suspected large-vessel abnormalities, allowing selection for intra-arterial angiography and serial monitoring of vascular abnormalities over time and during therapeutic intervention.

MRC European Carotid Surgery Trial: interim results for symptomatic patients with severe (70-99%) or with mild (0-29%) carotid stenosis. European Carotid Surgery Trialists' Collaborative Group

The European Carotid Surgery Trial is a multicentre trial of carotid endarterectomy for patients who, after a carotid territory non-disabling ischaemic stroke, transient ischaemic attack, or retinal infarct, are found to have a stenotic lesion in the relevant (ipsilateral) carotid artery. Over the past 10 years 2518 patients have been randomised, and the mean follow-up is now almost 3 years among the 2200 thus far available for analysis of the incidence of strokes that lasted more than 7 days. For the patients with "moderate" (30-69%) stenosis on their prerandomisation angiogram the balance of surgical risk and eventual benefit remains uncertain, and full recruitment continues. For 374 patients with only "mild" (0-29%) stenosis there was little 3-year risk of ipsilateral ischaemic stroke, even in the absence of surgery, so any 3-year benefits of surgery were small, and were outweighed by its early risks. For 778 patients with "severe" (70-99%) stenosis, however, the risks of surgery were significantly outweighed by the later benefits: although 7.5% had a stroke (or died) within 30 days of surgery, during the next 3 years the risks of ipsilateral ischaemic stroke were (by life-table analysis) an extra 2.8% for surgery-allocated and 16.8% for control patients (a sixfold reduction, p less than 0.0001). There was also a small reduction in other strokes, and at 3 years the total risk of surgical death, surgical stroke, ipsilateral ischaemic stroke, or any other stroke was 12.3% for surgery and 21.9% for control (difference 9.6% SD 3.3, 2p less than 0.01). The main concern was to avoid disabling or fatal events, and, among severe stenosis patients, 3.7% had a disabling stroke (or died) within 30 days of surgery, an extra 1.1% surgery versus 8.4% control (p less than 0.0001) had a disabling or fatal ipsilateral ischaemic stroke by 3 years, and the total 3-year risk of any disabling or fatal stroke (or surgical death) was 6.0% surgery versus 11.0% control (overall difference 5.0% SD 2.3, 2p less than 0.05); but, for disabling or fatal stroke the control risks seemed to diminish after the first year, so delay of surgery by just a few months after clinical presentation might make this overall difference non-significant.

Perioperative stroke. Part I: General surgery, carotid artery disease, and carotid endarterectomy

Although stroke, defined as a focal neurological deficit lasting more than 24 hr, is uncommon in the perioperative period, its associated mortality and long-term disability are high. No large-scale data are available to identify the importance of recognized risk factors for stroke in the perioperative period. A review of the literature shows that the incidence and mechanism of its occurrence are influenced by the presence of cardiovascular disease and the type of surgery. The most common cause of perioperative stroke is embolism. In non-cardiac surgery, the incidence of perioperative stroke is higher among the elderly. Properly administered, controlled hypotension is associated with minimal risk of stroke. Cerebral vasospasm may be the cause of focal cerebral ischaemia in eclamptic patients, and the aggressive treatment of hypertension may exacerbate the neurological damage. The risk of stroke associated with carotid endarterectomy is closely related to the preoperative neurological presentation, and the experience of the surgical/anaesthetic team. Symptomatic cerebrovascular disease, acute stroke, asymptomatic carotid lesions, preoperative assessment of risk, local and general anaesthesia, cerebral protection and monitoring during carotid endarterectomy are discussed with reference to reducing the risk of perioperative stroke. Adequate monitoring and protection have minimized the risk of ischaemia from carotid clamping, and the major mechanism of stroke is embolization.

The diminishing role of diagnostic arteriography in carotid artery disease: duplex scanning as definitive preoperative study

In an effort to eliminate the inherent neurologic morbidity associated with arteriographic investigation, we have increasingly relied upon duplex scans of the extracranial carotid arteries prior to endarterectomy. The percentage of patients undergoing carotid endarterectomy without arteriograms has increased from 5% in 1984 to 69% during 1988-1989. Initially, carotid endarterectomy without arteriography was limited to patients with hemispheric symptoms and relative contraindications. Over the course of the study from 1984-1989, indications for operation were similar for patients having carotid endarterectomy on the basis of duplex scan alone or following arteriography. The perioperative outcome for these patients undergoing duplex scan (n = 255) and arteriography (n = 484) were similar for stroke (2.4%) versus 2.7%, p = NS) and death (0% versus 0.4%, p = NS). Stratification of groups by indication did not show any significant differences in outcome. Duplex scans were sufficiently accurate to replace preoperative arteriograms in identifying significant stenoses at the carotid bifurcation, including asymptomatic disease. Lack of information regarding intracranial arterial occlusive disease did not adversely affect perioperative outcome. Carotid arteriography can be used selectively when duplex scans are technically difficult, when physical examination or scans suggest either inflow (arch) disease or diffuse, distal internal carotid plaque, or when cerebral symptoms are not sufficiently explained by duplex findings.

Investigation of acute stroke: what is the most effective strategy?

Techniques of investigation of acute stroke syndromes have progressed rapidly in recent years, outpacing developments in effective stroke treatment. The clinician is thus faced with a variety of tests, each with different cost implications and each altering management to a greater or lesser extent. This review will concentrate on the basic tests which should be performed for all strokes (full blood count, ESR, biochemical screen, blood glucose, cholesterol, syphilis serology, chest X-ray and electrocardiogram). Additional tests may be required in selected cases: CT scan to diagnose 'non-stroke' lesions, to exclude cerebral haemorrhage if anti-haemostatic therapy is planned, and to detect strokes which may require emergency intervention (such as cerebellar stroke with hydrocephalus); echocardiography to detect cardiac sources of emboli; and in a few cases lumbar puncture and specialized haematological tests. Other tests, which are currently research tools, may be suitable for widespread use in the future including NMR, SPECT and PET scanning.

Transient ischemic attacks: an update

This is a review of extant concepts of transient ischemic attacks (TIAs), their definitions, prognostic significance, pathogenesis, physiology, and management. The natural history of TIAs depends upon the risk factors of the population group studied, so that therapeutic trials should be controlled and randomized and not dependent upon published natural history data. A strong association between TIAs and coronary artery disease has now been established. It may be difficult to establish the cause or pathogenesis of TIAs in any given patient in view of the relatively poor correlation between the patient's symptoms and location of arterial plaques. Recent studies have suggested mechanisms aside from impaired perfusion or embolization from carotid plaques or vertebral basilar disease. There are no proven indications for carotid endarterectomy, a procedure which has been excessively used in the United States, but presently ongoing prospective, randomized, controlled multi-center studies will likely resolve this important issue. Neither is there scientific validation for the use of long-term anticoagulants, but data support the efficacy of ASA in reducing the incidence of stroke and myocardial infarction in patients with TIAs.

The role of imaging in the management of cerebral and ocular ischaemia

The last decade has seen several major technological advances in vascular neuroradiology, the most clinically significant of which have been the facility to image the brain and the extracranial carotid bifurcation noninvasively with accuracy and safety. Another major advance has been unequivocal evidence from formal statistical overviews that antiplatelet therapy, particularly aspirin, reduces the risk of serious vascular events by about 25%. These advances have changed clinical practice such that most patients presenting with symptoms suggestive of cerebral ischaemia should now have cranial CT to exclude intracerebral hemorrhage, not only because the causes and prognosis of cerebral ischaemia differ from those of intracerebral hemorrhage, but because many patients with cerebral ischaemia should be considered for antiplatelet therapy. Besides the use of long term antiplatelet therapy and control of vascular risk factors, other acute treatment options are limited with the possible exception of anticoagulation, thrombolysis, cytoprotective agents and carotid endarterectomy. If, as seems likely, the current clinical trials show that carotid endarterectomy plus medical therapy improve upon the stroke-free survival of patients treated medically, at least in symptomatic patients with severe stenosis, the number of carotid endarterectomies performed will increase considerably because carotid bifurcation disease is the most common cause of cerebral and ocular ischemic events. It will then be even more important to be able to obtain accurate anatomical and physiological information about the extracranial and intracranial circulations with utmost safety. Duplex ultrasound is currently the noninvasive screening method of choice for carotid bifurcation disease because it is available, relatively cheap, and reasonably accurate. It not only images the vessel lumen and degree of stenosis, but also the morphology of the vessel wall and associated plaque, the relevance of which is still uncertain in the pathogenesis of cerebral and ocular ischaemia. A major limitation of duplex sonography is that it cannot reliably distinguish tight stenosis from occlusion and it does not image the proximal or distal carotid circulation. The aim of newer techniques will be to distinguish tight extracranial carotid stenosis from occlusion and to provide anatomical, physiological and pathological information about the intracranial circulation and ischemic lesions (in view of potential for thrombolytic therapy of major intracranial vessel occlusion) with safety and reproducible accuracy.

A simple method to improve the accuracy of non-invasive ultrasound in selecting TIA patients for cerebral angiography

A prospective study is reported of the ability of B mode ultrasound imaging and continuous wave Doppler flow studies to detect different degrees of stenosis of the extracranial internal carotid artery (ICA) in 186 arteries in 99 patients with transient ischaemic attacks (TIA) and minor ischaemic stroke. A simple mathematical equation has been developed which combines the image and flow data to provide a single predictor of the degree of angiographic stenosis which has advantages over either ultrasonic modality used alone. The sensitivity and specificity of the predictive model in the detection of stenosis greater than or equal to 25% was 73% and 98%, of stenosis greater than or equal to 50% was 90% and 93%, of stenosis greater than or equal to 75%, 65% and 99% and occlusion 100% and 94% respectively. The principal clinical value of ultrasound screening is to spare patients with "non-significant" stenosis the risk of unnecessary angiography. Thus a simple measure of the Duplex screening tests' performance is the proportion of all strokes occurring as a complication of angiography that are avoided by changing the investigation policy from "angiograms for all carotid TIA and minor ischaemic stroke patients" to "angiograms for all patients with abnormal ultrasound results". If Duplex scanning were used to select patients most likely to have a significant abnormality on angiography, depending on the degree of stenosis to be detected, 52-85% of angiographic strokes might be avoided. If the predictive equation were used 62-88% of angiographic strokes might be avoided.