[Role of duplex ultrasonography of the ophthalmic artery in internal carotid artery stenosis]

BACKGROUND

Duplex sonographic visualization of a retrogradely perfused ophthalmic artery (AO) as an expression of an existing collateral supply in high-grade stenosis of the internal carotid artery (ACI) is a widely used and validated tool. After revascularization there may be another reversal of flow. Recently, the question of whether knowledge of the flow direction of the AO before and after implantation of a stent can be used as an outcome predictor has been posed more frequently.

METHODS AND RESULTS

In this article, the method of duplex sonographic assessment of the AO is explained more elaborately and we present a case of a patient with 75% restenosis of the left ACI with contralateral chronic occlusion of the right ACI. We focus on the special aspect that the ipsilateral AO was initially perfused retrogradely and that postinterventionally there was a flow reversal to a physiological anterograde flow. The case report is used to illustrate the value of duplex sonographic visualization of the AO.

CONCLUSION

Our case report is able to illustrate two aspects: On the one hand, the AO can be perfused retrogradely in the specific case of chronic ACI occlusion of the opposite side, even when the ACI stenosis of the considered side is less than 80%. On the other hand, the AO can offer added diagnostic value as a follow-up parameter for re- or in-stent stenoses.

Collateral Assessment by CT Angiography as a Predictor of Outcome in Symptomatic Cervical Internal Carotid Artery Occlusion

BACKGROUND AND PURPOSE

Cervical internal carotid artery occlusion can present with varied clinical manifestations such as transient ischemic attack, stroke, and chronic ocular ischemia, or can be asymptomatic. The outcome in these patients is considerably influenced by cerebral hemodynamic compensatory adaptation of the intracranial collateral pathways. Our aim was to study whether collateral circulation as assessed by CT angiography can predict 3-month outcome and initial stroke severity in patients with symptomatic cervical ICA occlusion.

MATERIALS AND METHODS

This was a retrospective study of 65 patients with symptomatic cervical ICA occlusion from January 2011 to December 2013. The collateral vessels (anterior and posterior communicating arteries, ophthalmic artery, and leptomeningeal arteries) were assessed by CTA. The outcome at 3 months was defined as poor if the modified Rankin Scale score was ≥3.

RESULTS

The mean age of subjects was 57 ± 11.6 years (range, 32-80 years), and 92% were men. Thirty-three (50.8%) patients had poor outcome. Absence of the ipsilateral ophthalmic artery, poor leptomeningeal collaterals, and <2 collaterals were predictors of stroke severity at onset and poor 3-month outcome in univariate analysis. In the multiple logistic regression analysis, inadequate flow through the secondary collaterals (ipsilateral ophthalmic artery or leptomeningeal collaterals; OR, 4.5; 95% CI, 1.4-14.9; P = .01) and higher NIHSS score at stroke onset (OR, 19.2; 95% CI, 2.2-166.2; P = .007) independently predicted poor outcome at 3 months.

CONCLUSIONS

Assessment of collateral circulation with CTA can be a useful predictor of 3-month outcome in patients with symptomatic cervical ICA occlusion.

Perioperative transorbital Doppler flow imaging offers an alternative to transcranial Doppler monitoring in those patients without a temporal bone acoustic window

Transcranial Doppler has been used to identify microembolic signals before, during and after carotid endarterectomy, but 10% to 15% of patients are reported not to have suitable temporal bone window. The aim of this study was to assess the feasibility of transorbital Doppler monitoring of patients with absent temporal bone acoustic window. Between 2005 and 2008, those patients with absent temporal bone acoustic window were assessed for a transorbital acoustic window. During the study period, 318 carotid endarterectomy were performed. In the 29 (9.1%) with absent temporal bone acoustic window, 25 (86%) had satisfactory transorbital acoustic windows, consequently only four (1.2%) of patients could not be monitored postoperatively. One patient required postoperative transorbital acoustic windows directed glycoprotein IIb/IIIa receptor antagonist infusion due to excessive carotid microembolisation to prevent stroke. This is the first description of the use of transorbital flow imaging to determine postoperative cerebral blood flow, microembolic load and to direct the use of intravenous antiplatelet agents.

Right-to-left-shunt detected by c-TCD using the orbital window in comparison with temporal bone windows

PURPOSE

There have been some reports on right-to-left shunt as a cause of cryptogenic stroke. Although contrast transcranial Doppler (c-TCD) can detect RLS, an insufficient temporal window has occasionally restricted its applicability. Thus, we compared the rates of detecting RLS among temporal windows for the middle cerebral arteries (MCAs) and the orbital window for the internal carotid artery (ICA) on c-TCD.

METHODS

We used c-TCD to detect RLS in patients with suspected ischemic stroke. We enrolled patients who had both sufficient bilateral temporal windows for MCAs and a right orbital window for ICA and performed c-TCD using all three windows simultaneously.

RESULTS

We enrolled 106 consecutive patients and identified microembolic signals (MES) in 30 (28%) of them. Among these 30 patients, 15 had MES from all 3 windows. When these 30 patients were defined as being positive for RLS, the rates of detection were 67%, 73%, and 80% from the right temporal, left temporal, and right orbital windows, respectively (P= .795).

CONCLUSION

The right orbital window as well as the temporal window for c-TCD could detect RLS. Insonation from the orbital window should be useful for patients who lack temporal windows.

Wall shear stress gradient analysis within an idealized stenosis using non-Newtonian flow

OBJECTIVE

The endothelium is functionally regulated by the magnitude and spatiotemporal gradients of wall shear stress (WSS). Although flow separation and reversal occur beyond high-grade stenoses, little is known of the WSS pattern within clinically relevant mild to moderate stenoses.

METHODS

An axisymmetric geometry with 25, 50, and 75% stenosis criteria (quantified in accordance with the North American Symptomatic Carotid Endarterectomy Trial) was used to generate a high-resolution, hybrid, tetrahedral-hexahedral computational mesh with boundary-layer enrichment to improve near-wall shear stress gradient (WSSG) computation. Time-dependent computational fluid dynamic analysis was performed using a non-Newtonian Carreau-Yasuda model of blood to yield the shear-dependent viscosity.

RESULTS

Transition to secondary flow patterns was demonstrated in stenoses of 25, 50, and 75%. A focal region with near-wall flow reversal and retrograde WSS was identified within the stenosis itself and was found to migrate cyclically during the cardiac pulse. A zone of zero WSS and divergent WSSG that shifts in toward the throat with increasing stenotic severity was identified. Focal zones of high WSSG with converging and/or diverging direction were uncovered within the stenosis itself, as were expected changes in the distal poststenotic region. These zones of divergent WSSG shift over a substantial length of the stenosis during the course of the cardiac cycle.

CONCLUSION

Luminal WSS demonstrates dynamic direction reversal and high spatial gradients within the distal stenosis throat of even clinically moderate lesions. These findings shed light on the complex vessel wall hemodynamics within clinical stenoses and reveal a mechanical microenvironment that is conducive to perpetual endothelial functional dysregulation and stenosis progression.

Collaterals in acute stroke: beyond the clot

Collateral circulation is a fundamental determinant of stroke pathophysiology. Distal arterial embolism and hypoperfusion resulting from severe proximal arterial stenosis may be offset by collateral flow. Collaterals influence whether or not infarction results. The detection and characterization of arterial deoxygenation and other consequences of collateral perfusion depend on neuroimaging techniques. Imaging advances will further the understanding of clinical correlates, including collateral sustenance and collateral failure, and possibly promote the development of collateral therapeutics. Refinements of perfusion imaging protocols may quantify the delay and dispersion of collateral flow more accurately. This review explores the role of collateral flow in acute ischemic stroke and describes the imaging modalities used to investigate phenomena "beyond the clot."

Transcranial Doppler in Acute Stroke

Transcranial Doppler (TCD) is an evolving neurovascular ultrasound technique that has an established diagnostic and potential therapeutic role in acute stroke management. Angiographically validated criteria for circle-of-Willis occlusion and thrombolysis in brain ischemia classification of residual flow have set the stage for the further development of this technique. TCD has shown its clinical value in thrombolysis monitoring and early emboli detection. The therapeutic effect requires confirmation and may be enhanced further by nanobubble technologies.