Echo-enhanced transcranial color-coded duplexsonography to study collateral blood flow in patients with symptomatic obstructions of the internal carotid artery and limited acoustic bone windows

Color Doppler ultrasonography for predicting the patency of anastomosis after superficial temporal to middle cerebral artery bypass surgery

BACKGROUND

Color Doppler ultrasonography (CDUS) is used to evaluate the surgical success and postoperative hemodynamic changes of patients who receive superficial temporal to middle cerebral artery (STA-MCA) bypass surgery. Previous studies enrolled small populations, and difficulties interpreting the results have limited their use in clinical settings.

OBJECTIVE

We attempted to determine the feasibility of using CDUS to evaluate STA hemodynamics and identify the most reliable parameter as a new clinical implication for determining bypass patency.

METHOD

Twenty-six patients who underwent STA-MCA bypass surgery were prospectively enrolled. Four times CDUS and two times digital subtraction angiography (DSA) were performed. The CDUS parameters were compensated using the ratio of the operated to the non-operated sides (R1) and compared before and after surgery (R2). The CDUS parameters are then compared with the patency on DSA by statistical analyses.

RESULTS

Increased CDUS parameters of the mean flow rate (MFR) and cross-sectional diameter (CSD) showed significant correlations with good patency on DSA. The R2 at 1 month was identified as the most reliable parameter for predicting the patency in both MFR and CSD. Their cutoff values were 1.475 and 1.15, respectively.

CONCLUSION

CDUS can be utilized for predicting the patency after STA-MCA bypass surgery; if the postoperative (compensated and compared) CDUS parameters increased by more than 47.5% in the MFR or 15% in the CSD, the patency of the anastomosis on DSA would be good.

Intracranial atherosclerotic disease

Atherosclerotic disease of the intracranial arteries is responsible for at least 10% of ischaemic strokes worldwide. Symptomatic disease has been extensively studied in the past few years, using diagnostic methods including multi-slice computed tomography and high resolution magnetic resonance imaging. A literature search was performed using PubMed and OvidSP between 1984 and May 2013. Variations of the terms 'intracranial atherosclerosis' plus 'ischemic stroke', 'plaque', 'morphology', 'imaging' were used and a combination of them. The reference lists of identified articles were also consulted for additional references. Amongst symptomatic patients the prevalence of intracranial atherosclerotic disease is around 10%, depending on race ethnicity, and the diagnosis requires the presence of ≥50% stenosis in the territory of the symptomatic vessel in a patient with stroke or transient ischaemic attack. The prognosis of intracranial atherosclerotic disease related stroke is poor. Although risk factor control can lead to a better outcome of intracranial atherosclerotic disease related strokes, the significance of asymptomatic disease is still a matter of debate.

Extent of spontaneous cross-flow via the anterior communicating artery in steno-occlusive carotid artery disease

PURPOSE

Our purpose was to evaluate the agreement of transcranial color-coded duplex sonography (TCCS) measurements and intra-arterial digital subtraction angiography (DSA) findings in determining the extent of spontaneous cross-flow via the anterior communicating artery (AcoA) in patients with internal carotid artery (ICA) stenosis.

METHODS

Thirty adult patients with suspected uni- or bilateral high-grade carotid artery stenosis were prospectively examined by DSA and angle-corrected TCCS. The extent of cross-flow was determined considering retrograde flow in the ipsilateral anterior cerebral artery (ACA) and sideto-side differences of the A1-segments of the ACA and middle cerebral arteries (MCAs) by both techniques. Cross-flow was angiographically categorized by means of a four-step scale. DSA findings were correlated with side-to-side differences in mean blood flow velocity as well as flow direction measured by TCCS.

RESULTS

Twenty-seven of 30 patients had a uni- or bilateral ICA stenosis of >49%. Excellent agreement between TCCS and DSA was evaluated for the detection of lack (grades 0 and 1) or presence (grades 2 and 3) of reversed flow in the ACA (sensitivity 100%, specificity 93%, positive predictive value 94%). Post hoc analysis of the mean velocities in the ACA and MCA revealed a side-to-side difference of 25 cm/s as a cutting point allowing for definition of a corresponding four-grade scale for ultrasound. However, full agreement, i.e.same grade of cross-flow detected by both techniques, was only found in 17(57%) of 30 cases.

CONCLUSIONS

Non-invasive TCCS is reliable for detecting reversed flow in the ACA in patients with ICA stenosis. However, there is only a moderate agreement between angiography and TCCS in quantifying the extent of spontaneous anterior cross-flow because different information on the intracranial hemodynamics may be obtained.

Clinical utility of echocontrast agents in neurosonology

INTRODUCTION

Neurosonological investigations of the extracranial and intracranial brain supplying arteries are helpful in the assessment of stroke and stroke-prone patients.

METHODS

In this paper we review the indications, application and advantages of second-generation (gas-filled) microbubble contrast agents such as SonoVue.

RESULTS

Gas-filled microbubbles have a strong echo enhancing effect and produce enhancement for several minutes, enabling the sonographer to perform the investigation with a single injection or two or three repeated injections without the need for continuous administration. Echocontrast agents provide better delineation of normal blood flow, occlusions, pseudo-occlusions, stenoses, and collaterals in the extracranial and intracranial vascular beds. They are of particular value during transcranial color-coded transcranial duplex investigations via the temporal and occipital window.

CONCLUSIONS

Echocontrast agents give additional information on the patient's vascular situation that is often crucial to planning further diagnostic and therapeutic steps. The use of second-generation gas-filled microbubbles, such as SonoVue in transcranial neurosonology, may help to avoid unnecessary, expensive and potentially harmful additional investigations such as intra-arterial DSA. Future applications include the visualization of brain tissue perfusion.

Absent collateral function of the circle of Willis as risk factor for ischemic stroke

BACKGROUND

Autopsy studies show a higher prevalence of circle of Willis anomalies in brains with signs of ischemic infarction. Our goal was to examine the collateral function of the circle of Willis in ischemic stroke patients and to assess in a case-control study if a collateral deficient circle of Willis is a risk factor for ischemic stroke in patients with severe internal carotid artery (ICA) occlusive disease.

METHODS

Our case-control study included 109 patients with an acute ischemic stroke in the anterior circulation and 113 patients with peripheral arterial disease and no known history of cerebral ischemia. The collateral function of the anterior and posterior communicating arteries of the circle of Willis was assessed by means of transcranial color-coded duplex ultrasonography (TCCD) and carotid compression tests.

RESULTS

TCCD was successfully performed in 75 case patients (mean age 64 years, range 41-91 years) and in 100 control patients (mean age 61 years, range 35-89 years). In 26 cases and 19 controls, a >/=70% stenosis or occlusion of the ICA was found. A nonfunctional anterior collateral pathway in the circle of Willis was found in 33% of the cases and in 6% of the controls (p < 0.001). The posterior collateral pathway was nonfunctional in 57% of the cases and in 43% of the controls (p = 0.02). In patients with severe ICA occlusive disease, the odds ratios of a nonfunctional anterior and a nonfunctional posterior collateral pathway were 7.33 (95% confidence interval, CI, = 1.19-76.52) and 3.00 (95% CI = 0.77-12.04), respectively.

CONCLUSIONS

Patients who suffer ischemic stroke in the anterior circulation have a higher incidence of collateral deficient circles of Willis than those with atherosclerotic vascular disease without ischemic cerebrovascular disease. The presence of a nonfunctional anterior collateral pathway in the circle of Willis in patients with severe ICA occlusive disease is strongly associated with ischemic stroke.

Hemodynamic flow patterns evaluated by transcranial color-coded duplex sonography after STA-MCA bypass for internal carotid artery occlusion

Extracranial-intracranial (EC-IC) bypass surgery had been widely performed for the treatment of internal carotid artery occlusion. However, it is presently difficult to predict how the bypass flow will contribute to intracranial circulation. We examined intracranial hemodynamics by transcranial color-coded duplex sonography (TCCD) after superficial temporal artery (STA)-middle cerebral artery (MCA) bypass and retrospectively studied the relationship between the postoperative contribution of the bypass flow and the preoperative collateral circulation and cerebrovascular perfusion status in 10 patients. Hemodynamics in the MCA detected by TCCD were classified into three patterns. In pattern A, perfusion of the whole MCA area is completely dependent on the bypass flow. In pattern B, perfusion of the M2 segment is dependent on the bypass flow, but perfusion of the M1 segment is independent of the bypass flow. In pattern C, perfusion of the whole MCA area is supplied by collateral flow and the bypass does not function efficiently. Preoperative absence of collateral flow via anterior communicating artery and cerebral perfusion status type 3 (reduced regional cerebral blood flow and regional cerebral vasoreactivity) seems to predict hemodynamic usefulness of the bypass flow after surgery. TCCD is an easy and noninvasive method for evaluating intracranial cerebral circulation after EC-IC bypass surgery.

Impact of ultrasound contrast agents in cerebrovascular diagnostics

This review gives a summary on current ultrasound contrast agents and their composition. Methods of brain imaging using UCA, like harmonic imaging and acoustic emission, are also described. Besides contrast-enhanced conventional color duplexsonography of the extracranial brain supplying arteries, transcranial contrast investigation of the basal cerebral arteries and visualization of cerebral microcirculation are also discussed in this paper. Another main topic are the interactions between UCA, human tissue and the ultrasound system.