Poststenotic flow and intracranial hemodynamics in patients with carotid stenosis: transoral carotid ultrasonography study

Abstract

Background and purpose: In severe carotid stenosis, blood supply via the poststenotic internal carotid artery (ICA) and collateral pathways determine cerebral perfusion. We investigated whether poststenotic flow on transoral carotid ultrasonography (TOCU) is predictive of cerebral hemodynamics.

Methods: Eighty-eight patients with unilateral carotid stenosis underwent TOCU to analyze blood flow velocity and poststenotic diameter of the extracranial ICA. Intracranial collaterals and cerebral hemodynamics were assessed with selective angiography and single photon emission CT.

Results: Poststenotic diameter (P <.0001) and velocities (peak systolic velocity [PSV], time-averaged mean velocity [TMV], end-diastolic velocity [EDV]; all P < or = .009) decreased with stenotic severity. Poststenotic diameter was correlated with PSV (r=0.36, P=.0005), EDV (r=0.32, P=.002), and TMV (r=0.39, P=.0001). Poststenotic flow was significantly lower with collateral pathways than without pathways (P < or = .02) and significantly decreased as the number of the collaterals increased (P <.0001). Flow <5 mL/s indicated collaterals (81% sensitivity, 80% specificity). When flow was <5 mL/s, the asymmetry index in the middle cerebral artery (MCA) territory was significantly low during rest (P=.003) and after acetazolamide challenge (P=.006). Poststenotic flow velocity was associated with baseline (P=.007) and postacetazolamide (P=.0009) MCA asymmetry indexes.

Conclusion: Poststenotic ICA flow measured with TOCU reflects collateral flow and cerebral hemodynamics in patients with severe carotid stenosis. This technique may provide new parameters for screening patients with hemodynamically significant carotid stenosis.

Fig 1.

Variables in the poststenotic portion of the ICA plotted against the number of the collateral pathways. Asterisk indicates P < .005 versus patients with no collaterals; section symbol, P < .005 versus patients with one collateral; andnumber sign, P < .005 versus patients with two collaterals. A, Poststenotic diameter. B, Poststenotic blood flow.

Fig 2.

Sensitivity-specificity curve. Optimal threshold value of poststenotic blood flow for predicting collateral pathways is 5 mL/s.

Fig 3.

Baseline and postacetazolamide asymmetry index in the MCA territory plotted against poststenotic blood flow. Group I indicates patients with flow <5 mL/s; Group II, patients with flow ≥5 mL/s; asterisk, P < .005; and section symbol, P < .01 versus group II. A, Before acetazolamide. B, After acetazolamide.