Assessment of intracranial hemodynamics in carotid artery disease by transcranial Doppler ultrasound

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✓ Noninvasive transcranial Doppler recordings were correlated to the angiographic findings in 77 patients with carotid artery disease. Stenoses reducing the luminal area of the internal carotid artery by 75% or more also reduced the pulsatility transmission index (PTI) of the ipsilateral middle cerebral artery (MCA). The PTI is the pulsatility index of the artery under study expressed as a percent of the pulsatility index of another intracranial artery with presumed unimpeded inflow in the same individual. For stenoses in the 75% to 89% category, PTI reduction was significantly greater in patients with bilateral carotid stenosis, indicating an impaired potential for collateral flow in these patients. The PTI reduction probably reflects both the pressure drop across the stenosis and the cerebral autoregulatory response. Two criteria proved useful in demonstrating collateral MCA supply through the circle of Willis. On the recipient side, retrograde flow in the proximal anterior cerebral artery was demonstrated in 29 of the 31 patients when this flow pattern was disclosed angiographically. In 26 of these patients, the anterior cerebral artery on the supplying side also had clearly increased flow velocity. Increased flow velocities in the proximal posterior cerebral artery were present in 26 of the 30 vessels that were acting as a collateral channel to the ipsilateral MCA.

Article Information

Address reprint requests to: Karl-Fredrik Lindegaard, M.D., Department of Neurosurgery, Rikshospitalet, The National Hospital, Pilestredet 32, N-0027 Oslo 1, Norway.

© AANS, except where prohibited by US copyright law.

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Figures

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    Left: Determinations of systolic, diastolic, and time-mean values of the Doppler velocity spectrum outline (Vs, Vd and V, respectively). The pulsatility index, PI = (Vs−Vd)/V. Center: Transcranial flow velocity recordings. Probe position 1 is preferred for recordings from the middle and posterior cerebral arteries (MCA and PCA). The sampling volume is shown in position for MCA recordings. The sampling depth setting for these recordings is usually about 45 mm. The PCA is identified by aiming the probe slightly more posteriorly, using depth settings of about 65 mm. Probe position 2 is preferred for recordings from the anterior cerebral artery in individuals with more than one ultrasonic window. Right: Location of areas where the adult cranium usually is sufficiently thin to allow penetration of ultrasound for transcranial recordings of flow velocity (“ultrasonic windows”). Numbers correspond to probe positions shown center.

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    Transcranial Doppler identification of basal cerebral arteries in a healthy individual during a test occlusion of the common carotid artery (CCA) in the neck. The proximal segments of the middle and posterior cerebral arteries (MCA and PCA) have a normal flow direction toward the transducer. An ipsilateral CCA test occlusion reduces the absolute MCA flow velocity level, which reflects MCA inflow through collateral vessels (center). By contrast, the response in the PCA signal to this test is an increased velocity level, indicating the potential of this vessel as a collateral source (right).

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    Transcranial Doppler identification of the anterior cerebral artery (ACA) in the same healthy individual as monitored in Fig. 2. In the proximal anterior cerebral artery (ACA), the normal flow direction is away from the probe. Normally directed ACA velocity spectra are therefore shown below the zero line (left). Test occlusions of the common carotid artery (CCA) give rise to characteristic responses in the ACA flow velocity patterns.

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    In the 49 patients with unilateral internal carotid artery (ICA) stenosis, the middle cerebral artery (MCA) flow velocity (Vmca) on the side with ICA stenosis is presented, expressed as a percentage of Vmca on the normal side, and correlated with the percentage diameter of ICA stenosis. The median value decreases for ICA stenosis over 90%. Nevertheless, the ranges are wide with values from patients with total ICA occlusion (100% stenosis) overlapping even those from control individuals, owing to the MCA blood flow and Vmca being maintained when cerebral autoregulation is operative. The Vmca value is therefore quite insensitive to the hemodynamic effect of ICA stenosis. The numbers over each column denote the number of patients in each group.

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    Pulsatility transmission index (PTI) for middle cerebral artery (MCA) recordings correlated with percentage diameter of stenosis of the ipsilateral internal carotid artery (ICA) in patients with unilateral (open columns) and bilateral ICA stenosis (cross-hatched columns). A definite PTI drop occurred for ICA stenoses over 75%. For stenoses in the 75% to 89% range (darker column), PTI was significantly lower in patients with bilateral ICA stenosis compared to patients with unilateral ICA stenosis (p < 0.025). The potential for collateral flow is generally impaired in these patients. The numbers over each column denote the number of patient hemispheres in each group.

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    In the 49 patients with unilateral internal carotid artery (ICA) stenosis, the middle cerebral artery (MCA) flow velocity (Vmca) on the side with ICA stenosis is presented, expressed as a percentage of Vmca on the normal side. Correlation with the corresponding pulsatile transmission index (PTI) values shows no deviation from findings in control individuals for patients with PTI over 70, but PTI values below 60 were associated with a Vmca asymmetry that was significantly greater than in control individuals or in the other patients (p < 0.02). Also, note the successively lower Vmca with further PTI reduction. The numbers over each column denote the number of patients in each group. The findings in patients with total ICA occlusion (circled numbers) showed a great diversity owing to individual variations in collateral capacity. Results in Control Groups A and B are given for comparison.

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    Transcranial Doppler findings in a 58-year-old man in whom left carotid angiography confirmed total internal carotid artery (ICA) occlusion, right carotid angiography revealed no ICA stenosis but did indicate collateral filling across the midline into the left middle cerebral artery (MCA), and the vertebral angiograms were normal with no filling of collateral vessels. The left MCA velocity outline has a reduced pulsatility index (PI = 0.76) when compared to the recording from the right MCA (PI = 1.00). The absolute velocity levels (Vmca) are about equal. The right MCA and the posterior cerebral artery (PCA) velocity outlines show identical pulsatility. The pulsatility transmission index (PTI) for the left MCA is 76. On the right side, an anterior cerebral artery (ACA) collateral channel to the left MCA is indicated since the Vaca (upper right) is increased to 175% of the right Vmca. Retrograde flow velocities in the left ACA confirm this finding (lower right).

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    Transcranial Doppler findings in a 66-year-old man in whom right carotid angiography revealed 90% stenosis of the extracranial internal carotid artery (ICA) and proximal anterior cerebral artery (ACA) filling by the right and left pericallosal arteries (distal ACA's) only, left carotid angiography showed total ICA occlusion, and vertebral angiography demonstrated left middle cerebral artery (MCA) filling through a collateral channel from the left posterior cerebral artery (PCA) but no filling of the left ACA. The pulsatile index and velocity for the MCA (PImca and Vmca, respectively) are about equal. The signal from the right PCA is more pulsatile (upper center), indicating impaired inflow to both MCA's (pulsatile transmission index: left MCA 72; right MCA 73). The left Vpca is 200% of the left Vmca, indicating collateral flow. The right Vaca (upper right) is 170% of the right Vmca. No flow was recorded in the left ACA.

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