Imaging of the intracranial vertebrobasilar system using color-coded ultrasound.

BACKGROUND: Anatomic variety and difficult accessibility of the vertebrobasilar arteries pose considerable problems to conventional ultrasound. We evaluated the diagnostic potential of transcranial color-coded sonography in the distal part of this system. METHODS: We insonated the intracranial section of the vertebrobasilar arteries through the foramen magnum window in 24 healthy individuals using a Doppler color flow imaging system in connection with a 2.5-MHz sector transducer. Magnetic resonance images in special inclination planes were performed and compared with the color-coded duplex images in five cases. RESULTS: The B-mode image of the craniocervical junction and the intracranial parenchymal structures in addition to the color-coded blood flow allowed an unambiguous identification of the vertebrobasilar arteries (vertebral artery, 96%; basilar artery, 79%; and posterior inferior cerebellar artery, 50%). Blood flow velocities were measured considering the insonation angles: vertebral arteries, 50/24 cm/sec (30 degrees); basilar artery, 59/28 cm/sec (4 degrees); and posterior inferior cerebellar artery, 56/30 cm/sec (20 degrees) [peak systolic/end diastolic blood flow velocity (mean angle correction)]. CONCLUSIONS: Transcranial color-coded sonography enables accurate identification and differentiation of the intracranial vertebrobasilar arteries and improves accuracy of Doppler measurements. It may prove useful for evaluation of tortuosity and for hemodynamic studies in this vascular territory.     

Chronic brainstem ischemia in subclavian steal syndrome

Subclavian steal syndrome is usually an incidental finding and rarely causes vertebrobasilar ischemia. We present a 58-year-old man who, over six months, experienced progressive slowing in both talking and walking. Cervical duplex sonography revealed severe stenosis of the right subclavian artery; fixed retrograde flow was noted in the right vertebral artery on transcranial Doppler. The hyperemia–ischemia cuff test resulted in considerable reduction in flow velocities in both posterior cerebral arteries. We attributed his slowness to chronic vertebrobasilar ischemia and surgical revascularization was performed. His symptoms subsided immediately after surgery. The improved perfusion in the posterior circulation was demonstrated on technetium-99 hexamethylpropyleneamine oxime single photon-emission CT. Early diagnosis and prompt treatment resulted in an improved quality of life.     

Cerebral autoregulation in middle cerebral artery territory precedes that of posterior cerebral artery in human cortex.

OBJECTIVE: Cerebral autoregulation tends to compensate changes in arterial blood pressure. This mechanism of cerebral blood flow regulation appears to be insufficient in orthostatic dysregulation in which mainly vertebrobasilar symptoms occur. To investigate this hypothesis, we compared cerebral autoregulation in the vascular territory of the carotic and vertebrobasilar vessel system using a leg cuff test to induce a drop in cerebral perfusion pressure. METHODS: We measured blood flow velocity in 10 healthy young volunteers (aged 26.7 +/- 0.3 years, 7 male) simultaneously in the middle and posterior cerebral artery with transcranial Doppler sonography. A leg cuff test was used to induce a sudden decrease in arterial blood pressure. Arterial blood pressure was measured with a non-invasive photoplethysmographic method. The averaged relative blood flow velocity changes due to the pressure step were compared between both vessel territories. RESULTS: After cuff release systolic (diastolic) blood flow velocity increased with a latency of 1.1 +/- 0.3 s (1.8 +/- 0.4 s). Due to a smaller decrease and identical time courses cerebral blood flow velocity recovery in the posterior cerebral artery precedes blood flow recovery in the middle cerebral artery by 0.9 +/- 0.3 s. DISCUSSION: Cerebral autoregulation in the carotid and vertebrobasilar system does not differ in the time course of the blood flow velocity recovery. Due to a smaller decrease in blood flow velocity recovery in the posterior cerebral artery precedes recovery in the middle cerebral artery by nearly 1 s.     

Preoperative risk assessment for carotid occlusion by transcranial Doppler ultrasound.

OBJECTIVES: An endovascular carotid balloon occlusion test with continuous intracranial monitoring by transcranial Doppler sonography was performed in 55 patients for prediction of tolerance of a required permanent occlusion of the carotid artery. METHODS: Blood flow velocities of the ipsilateral middle cerebral artery during occlusion were recorded and compared with clinical tolerance during an occlusion test as well as with postoperative outcome after an eventual permanent occlusion. To stress the capacity of the cerebral circulation to tolerate the occlusion acetazolamide was injected before occlusion in all patients. RESULTS: The onset of neurological symptoms during temporary occlusion was dependent on the percentage fall of mean blood flow velocity relative to baseline rather than on absolute flow velocities during the time of occlusion. Patients with a fall of mean flow velocity of less than 30% tolerated temporary and permanent occlusion, with the exception of two patients who developed an infarction due to thromboembolism after iatrogenic sacrifice of the carotid artery. Patients with a major decrease developed neurological symptoms during occlusion in 55% and, in cases of carotid ligation, a haemodynamic infarction occurred. CONCLUSION: The results show that transcranial Doppler monitoring as a part of an endovascular balloon occlusion test may be a reliable technique for preoperative risk assessment for permanent occlusion of the carotid artery.     

Transcranial color-coded sonography for vertebrobasilar disorders in end-stage renal disease

Because vertebrobasilar arterial disorders seem to be common in patients with end-stage renal disease, a neuroradiological evaluation of vertebrobasilar circulation is necessary for patients with possible vertebrobasilar insufficiency. In three patients on maintenance hemodialysis, contrast-enhanced transcranial color-coded real-time sonography (TCCS) through a suboccipital window delineated occlusion of bilateral vertebral arteries with reversal of the basilar artery, reversal of the left vertebral artery mimicking left subclavian steal phenomenon, and dolichoectasia of the basilar artery and bilateral vertebral arteries with signals of turbulent flow. TCCS has several advantages over computed tomographic angiography and magnetic resonance angiography, including the direction of blood flow, handy performance even during hemodialysis, and contrast agent free from nephrotoxicity. Thus, TCCS is useful in the evaluation of intracranial circulation in patients with end-stage renal disease.     

Transcranial Doppler Findings in Acute Spontaneous Recanalization of Middle Cerebral Artery Embolism

Three patients suspected of having acute middle cerebral artery occlusion were studied using transcranial Doppler sonography on admission and again during the following week. Initially, sonographic criteria for acute middle cerebral artery occlusion were present in all 3; however, follow-up studies revealed normal Doppler waveforms and blood flow velocities. Subacute recanalization of the occlusion has been previously studied with transcranial Doppler sonography and shown to have a characteristic temporal profile evolving over weeks. Acute recanalization, in contrast, is characterized by normalization of the affected vessel's sonographic pattern within days of initial occlusion.     

Demonstration of giant MCA aneurysm by transcranial duplex sonography and color Doppler imaging

Transcranial color Doppler sonography is a new diagnostic technique which allows real-time, colorcoded imaging of basal cerebral arteries, with simultaneous demonstration of parenchymal structures in the B-mode scan. With this technique we were able nonivasively to show a giant fusiform aneurysm of the middle cerebral artery (MCA) in an 11-year-old boy. Transcranial color Doppler sonography through the intact temporal bone demonstrated the size and location of the aneurysm and provided real-time imaging of the pulsating intra-aneurysmal flow. Additionally, duplex sonographic measurements of intravascular flow velocities within the aneurysm and the feeding and draining artery were possible. Postoperatively, patency of the MCA with reduced flow velocities after excision of the aneurysm could be shown. This is the first transcranial color Doppler report in a patient with an intracerebral aneurysm. In our opinion, transcranial color Doppler sonography offers new diagnostic possibilities in patients with cerebrovascular disorders.     

Quantitative Measurements of Blood Flow Velocity in Basal Cerebral Arteries with Transcranial Duplex Color-Flow Imaging: A Comparative Study with Conventional Transcranial Doppler Sonography

Transcranial duplex color-flow imaging is a new diagnostic method that allows visual display of blood flow in the basal cerebral arteries. This method allows determination of and correction for the Doppler angle of insonation. Conventional transcranial Doppler sonography has no imaging component and assumes a 0-degree Doppler angle for the calculation of flow velocities. The magnitude of the angle of insonation and the effect on flow velocity estimates have not been clearly defined. In order to evaluate the angle of insonation and the effect of angle correction on velocity readings, 50 patients referred for evaluation of cerebrovascular disease were studied. The mean age was 45 years (range, 24-62 yr). All were examined with conventional transcranial Doppler and transcranial duplex color-flow imaging. Specific vessels of the circle of Willis were identified by location, course, and direction of flow on color-flow images and by depth, direction of flow, and transducer orientation with conventional Doppler sonography. Visually controlled measurements of the Doppler angle of insonation were made by color-flow imaging. The data show that the mean angle of insonation was 33 degrees (± 15) in the middle cerebral artery, 35 degrees (± 17) in the anterior cerebral artery, 45 degrees (± 18) in the posterior cerebral artery, and 15 degrees (± 14) in the basilar artery. Angle-corrected peak systolic flow velocities were higher in all vessel segments (middle cerebral = 15%, anterior cerebral = 18%, posterior cerebral = 30%, and basilar = 3%), compared to uncorrected velocity readings by conventional Doppler sonography. Colorflow imaging facilitates determination of the angle of insonation and angle correction of flow velocity estimates. These data suggest that the angle of insonation is greater than previously appreciated. Angle correction yielded higher average flow velocities in all vessels. The clinical importance of these higher, angle-corrected velocities is not known.     

A simple test to assess cerebrovascular reserve capacity using transcranial Doppler sonography and acetazolamide

The goal of this study was the development of a simple bedside test to assess cerebrovascular reserve capacity using transcranial Doppler sonography. We studied 33 normal persons at rest and after stimulation of cerebral blood flow with 1 g acetazolamide. Their mean +/- SD increase in blood flow velocity in 54 middle cerebral arteries 10 minutes after stimulation was 24.4 +/- 9.2 cm/sec. We tried to validate the increase in blood flow velocity as cerebrovascular reserve capacity in 21 patients with obstructive carotid artery disease and symptoms of cerebral ischemia. The patients were studied using transcranial Doppler sonography and xenon-133 dynamic single-photon emission computed tomography after acetazolamide stimulation. Their increases in blood flow velocity (delta FV) and increases in cerebral blood flow (delta CBF) correlated significantly in both hemispheres (asymptomatic: Y = 0.32X + 10.65, r = 0.45, p = 0.04; symptomatic: Y = 0.36X + 2.28, r = 0.59, p = 0.004). There was no significant difference between the slopes of the regression lines. Blood flow velocity and cerebral blood flow at rest were not correlated. The increase in blood flow velocity after acetazolamide stimulation offers a simple and reliable method for assessing cerebrovascular reserve capacity.     

Pitfall of Electron Beam Computed Tomography Angiography in Diagnosis of Subclavian Steal Syndrome

A patient presented with vertebrobasilar insufficiency during exertion. Vertebral duplex and transcranial Doppler ultrasonography showed reversal of flow in both intracranial and extracranial vertebral and basilar arteries, suggesting bilateral subclavian and vertebrobasilar steal. Electron beam computed tomography angiography (CTA) showed no evidence of subclavian artery stenosis including normal vertebral artery origin on both sides. However, digital subtraction angiography revealed complete occlusion of both subclavian arteries with retrograde flow from both vertebral and basilar arteries to reconstitute both subclavian arteries. This false-negative finding on CTA in detection of subclavian steal syndrome (SSS) is due to inappropriate contrast administration technique and postprocessing method, inability to differentiate flow direction, and lack of hemodynamic time sequences. This study demonstrates a pitfall of CTA in diagnosis of SSS compared to more reliable hemodynamic information obtained by duplex and transcranial Doppler ultrasonography, and digital subtraction angiography.     

A patient with vertebrobasilar transient ischaemic attacks and provokable basilar steal

In a 65-year-old woman with vertebrobasilar transient ischaemic attacks (TIAs) and subclavian steal, a steal phenomenon in the basilar artery could be demonstrated by transcranial Doppler sonography after provocation with postischaemic hyperaemia of the arm on the affected side. It was not possible to provoke symptoms or signs at the time. The significance of finding a steal phenomenon in the basilar artery even in a patient with a history of vertebrobasilar TIAs is discussed.     

Blood flow velocities in middle cerebral artery branches after subarachnoid hemorrhage.

In a prospective study, 55 patients were examined by transcranial duplex sonography (TCCS) after subarachnoid hemorrhage (SAH) to determine whether additional transcranial duplex examination on the middle cerebral artery M2 segments would aid in the examination of the MCA stem segment. The mean blood flow velocities and pulsatility index were correlated to the occurrence of delayed ischemic neurologic deficits (DIND). Out of 47 patients included, 21 did not experience any delayed deficit (group I), 15 did (group II), and in 11 the extent to which vasospasm contributed to a neurologic deficit was unclear (group III). The highest blood flow velocity and the greatest increase of mean blood flow velocity on 1 day were significantly higher in groups II and III both in M1 and in M2. In 10 patients in group II, where the onset day of DIND was known exactly, Doppler data indicating ischemia before or at the time of DIND were observed in nine. In eight patients, Doppler of the MCA stem alone would have provided enough information to recognize the risk of symptomatic vasospasm; in one patient, only the M2 Doppler gave an indication of ischemic complication. Transcranial duplex sonography may provide additional information to TCD by accurate delineation of M1/M2 vasospasm and therefore may help plan cerebral angiography and neurointerventional treatment.     

转颈对眩晕患者基底动脉流速的影响

目的　采用TCD观测转颈对正常人及眩晕患者基底动脉流速的影响。方法　正常对照组 3 6例 ,眩晕患者 3 1例 ,TCD常规检查椎 -基底动脉及转颈时基底动脉流速的变化。结果　正常人随年龄增大 ,椎 -基底动脉流速下降 ,转颈前后基底动脉流速差异无显著性 ;眩晕患者椎 -基底动脉流速下降 ,转颈后基底动脉流速明显下降 ,较转颈前差异有显著性 (P <0 .0 5 )。结论　转颈后基底动脉流速下降≥ 2 0 % ,即为转颈试验阳性 ,提示患者椎—基底动脉系统代偿能力差 ,存在椎动脉狭窄等病变的可能 ,需进一步检查     

Effect of Hyperventilation on Cerebral Blood Flow Velocity in Preeclamptic Pregnancies: Is There Evidence for an Altered Cerebral Vasoreactivity?

The purpose of this study was to investigate cerebral arteriolar vasoreactivity function in preeclampsia. Preeclamptic (n = 26) and healthy pregnant (n = 22) women underwent transcranial Doppler sonography of the middle cerebral artery at rest and after 60 seconds of hyperventilation (HV). Systolic, diastolic, and mean blood flow velocities were recorded. The percentage change of the blood flow velocities after HV was calculated. Mean blood flow velocity of the middle cerebral artery was higher in preeclamptic women as compared with healthy pregnant women. No difference could be detected in percentage change of middle cerebral artery blood flow velocities after HV between the two groups. There is no evidence of a small-vessel vasoconstriction among preeclamptic patients. The role of vasoconstriction of the large cerebral arteries and vasodilation of the resistance arterioles, as well as a combination of these 2 pathomechanisms, in determining cerebral blood flow in preeclampsia and eclampsia should be investigated in further studies.     

The Effects of Dolichoectasia on Transcranial Doppler Measurements

Transcranial Doppler sonography is used to evaluate intracranial hemodynamic changes associated with cervical and intracranial arterial lesions; however, studies of patients with cerebral ischemia and nonstenotic lesions are uncommon. This report presents the transcranial Doppler findings in 4 patients with cerebral arterial dolichoectasia demonstrated by angiography and brain computed tomography. Although blood flow velocities were decreased in all the arteries tested, the pulsatility and resistance indices were normal. Our results suggest that in patients with ischemic cerebrovascular disease, transcranial Doppler findings of low flow velocities should prompt consideration of dolichoectasia.     

Transcranial Doppler sonographic studies of cerebral autoregulation in Shy-Drager syndrome

Summary A study is reported of mean arterial blood pressure and heart rate in four patients suffering from Shy-Drager syndrome. Blood flow velocity in the middle cerebral artery (MCA) was recorded by transcranial Doppler sonography. Concomitant changes in cerebral blood flow and the effect of cerebral autoregulation were thus examined. During tilt (60°, head up) mean arterial blood pressure decreased by 40 mm Hg or 35%, while MCA blood flow velocity dropped by 14 cm/s or 28% (mean values). The lower percentage reduction in flow velocity may indicate a preserved cerebral autoregulation in central autonomic insufficiency.     

Prediction of symptomatic vasospasm after subarachnoid hemorrhage by rapidly increasing transcranial Doppler velocity and cerebral blood flow changes.

BACKGROUND AND PURPOSE: Increased transcranial Doppler velocities and regional cerebral perfusion defects have been well demonstrated in patients with subarachnoid hemorrhage, but the clinical significance of these changes has not been clearly defined, particularly in the presymptomatic stage of cerebral vasospasm. We have tested the hypothesis that a rapid, massive rise in Doppler velocity denotes progressive vasospasm by relating Doppler velocity increases to regional cerebral blood flow changes and to the subsequent clinical course. METHODS: Serial transcranial Doppler sonography was performed in 121 patients; 20 of these patients were selected for blood flow mapping on the basis of rapid increases (greater than 50 cm/sec/24 hr) in blood flow velocity. Cerebral blood flow was mapped by single-photon emission computed tomography using technetium-99m hexamethylpropyleneamine oxime. RESULTS: Ten of 15 patients studied before the onset of any deficit subsequently developed a focal neurological abnormality. In 14 of these 15 patients, and in a further five in which single-photon emission computed tomography was performed after the onset of a delayed neurological deficit, perfusion patterns were abnormal and correlated with sites of increased Doppler velocities. Four patients had zones of cerebral hypoperfusion but did not develop neurological deficit. CONCLUSIONS: Transcranial Doppler measurements can assist in identifying patients at risk of delayed ischemic deficit. Selection of patients for regional cerebral blood flow mapping studies and for prophylactic anti-ischemic therapy may be considered on this basis.     

Non-invasive diagnosis of intracranial lesions in the vertebrobasilar system. A comparison of Doppler sonographic and angiographic findings

The accuracy and the reliability of extracranial vertebral Doppler flow (continuous wave Doppler sonography) for the detection of intracranial vertebrobasilar lesions was studied prospectively in twenty-one patients with brainstem disturbances and/or coma. The Doppler findings were compared with cerebral angiography. Doppler sonography was highly reliable for both detection and exclusion of high grade intracranial vertebrobasilar lesions. The pathognomonic Doppler finding was an abrupt deceleration of the blood column during systole and stoppage or even reflux during diastole. The same blood flow alterations were found in two additional illustrative cases having therapeutically or brain-death induced blockages of the vertebral arteries. The pathophysiologic mechanisms of flow disturbances and the limitations of Doppler sonography in this area are discussed.     

Effects of thiopental on middle cerebral artery blood velocities: a transcranial Doppler study in children

The effect of an intravenous injection of thiopental on middle cerebral artery blood velocities was assessed by transcranial pulsed Doppler monitoring in 20 children: ten head-injured patients and ten control subjects. Thiopental induced a moderate but immediate decrease of middle cerebral artery blood velocities in both groups; this variation was significant (P<0.01) and more prolonged in the head-injured than in control patients. Transcranial Doppler ultrasonography thus appears to be suitable for monitoring children in intensive care units and could help to avoid the use of thiopental in patients with low cerebral artery blood flow velocity.     

Power-based versus conventional transcranial color-coded duplex sonography in the assessment of the vertebrobasilar-posterior system

Background: Power Doppler (PD) is a new ultrasonic technique that allows improved visualization of vascular structures. The aim of our study was to compare the ability of power-based transcranial color-coded duplex sonography (p-TCCS) to conventional transcranial color-coded duplex sonography (TCCS) and contrast-enhanced transcranial color-coded duplex sonography (CE-TCCS) in the visualization of the vertebrobasilar system. Methods: In 41 patients without cerebrovascular diseases, we evaluated and compared identification rates of major vessels of the vertebrobasilar system and branches using both ultrasound (US) techniques. In 9 patients we performed additional CE-TCCS studies. Furthermore, the possibility of visualization of the basilar artery (BA) and the vertebral arteries (VA) over the long course was investigated. Results: TCCS and p-TCCS were equally effective at showing the VAs (74 of 82 v 80 of 82), proximal segments of the BA (37 of 41 v 41 of 41) and P1 segments of the posterior cerebral artery (PCA) (72 of 82 v 82 of 82). However, the diagnostic sensitivity of p-TCCS was significantly better for peripheral segments of the PCA (34 of 82 v 68 of 82 for P2 and 2 of 82 v 24 of 82 for P3 segments, P<.001), distal parts of the BA (25 of 41 v 38 of 41, P<.01), the anterior inferior cerebellar artery (AICA) (0 of 82 v 8 of 82, P<.0001) and the posterior inferior cerebellar artery (PICA) (13 of 82 v 34 of 82, P<.001). Furthermore, using transtemporal coronal sections, p-TCCS allowed visualization of the BA over the complete course in connection with one or both VAs in half of the patients. Except P2 and P3 segments, CE-TCCS did not increase resolution compared with p-TCCS. Conclusions: PD offers significant advantages over color-coded sonography in imaging the BA and small-calibre vessels like the PICA, AICA, and peripheral segments of the PCA. P-TCCS in combination with TCCS increases the diagnostic sensitivity to identify vascular structures of the vertebrobasilar system.