Evaluation of cerebral circulation in patients with significant carotid artery stenosis.

Background: A significant proportion of ischaemic stroke episodes are caused by atherosclerotic lesions in extracranial arteries. Assessment of haemodynamical profile of cerebral arteries in both symptomatic and asymptomatic patients with carotid artery stenosis is of clinical importance.

Aim: To assess haemodynamic changes in cerebral arteries in patients with significant internal carotid artery (ICA) stenosis.

Method: Patients (n=109) were divided into the following groups: group I (GI) - 42 subjects (64.6+/-9.0 years) with asymptomatic ICA stenosis > or =70%; and group II (GII) - 67 subjects (63.4+/-7.1 years) after stroke. The control group consisted of 30 patients (60.3+/-8.9 years) without significant stenoses of extracranial arteries on USG and angiography. In all cases ultrasonographic evaluation of flow velocities and directions in cerebral arteries within the circle of Willis and collateral flow was performed.

Results: The severity of ICA stenosis did not differ significantly between GI and GII. Patients in GI had flow velocity in the middle cerebral artery (MCA) increased by 15.7% and by 40.8% in the anterior cerebral artery (ACA) contralateral to the ICA stenosis (p<0.001 and p<0.001), whereas in GII no significant changes in flow velocity in these arteries were observed in comparison with the control group. Patients in the groups I and II had lower flow velocities in MCA ipsilateral to the ICA stenosis, however values for GII patients were significantly lower than in GI patients (p<0.001). The presence of collateral circulation through the anterior and posterior communicating arteries (ACoA and PCoA) was similar in GI and GII; however, the flow velocities in the ipsilateral MCA and ACA were significantly higher in asymptomatic patients (GI). The frequency of active collateral circulation through both ACoA and PCoA increased along with the increase of ICA stenosis severity (p=0.003; p<0.001).

Conclusions: Collateral flow in the circle of Willis in subjects with ICA stenosis occurs equally often in symptomatic and asymptomatic patients; however, it is more efficient in patients without symptoms. The rate of development of collateral circulation depends on ICA stenosis severity. The important role in maintaining collaterals within the circle of Willis is played by ACoA, although in some patients MCA may also be supplied by PCoA.