Collateral ability of the circle of Willis in patients with unilateral internal carotid artery occlusion: border zone infarcts and clinical symptoms.

BACKGROUND AND PURPOSE The circle of Willis is regarded as the major source of collateral flow in patients with severe carotid artery disease. The purpose of the present study was to assess whether the presence of border zone infarcts is related to the collateral ability of the circle of Willis in symptomatic (transient ischemic attack, minor stroke) and asymptomatic patients with unilateral occlusion of the internal carotid artery (ICA). METHODS Fifty-one patients (35 symptomatic, 16 asymptomatic) and 53 control subjects were investigated. Patients had unilateral occlusion of the ICA and contralateral ICA stenosis between 0% and 69%. The directions of flow, on the side of the ICA occlusion, and the size of the component vessels in the circle of Willis were investigated with MR angiography. RESULTS On average, 92% of the patients without border zone infarcts (n=26) had willisian collateral flow compared with 60% of patients with border zone infarcts (n=25; P<0.05). This increase in collateral flow was caused by the high prevalence of collateral flow via the posterior communicating artery in patients without border zone infarcts (50% versus 12%; P<0.05). No statistically significant relation was found between the pattern of collateral flow via the circle of Willis and the presence of clinical symptoms. Nevertheless, asymptomatic patients with ICA occlusion demonstrated an increased diameter of the anterior communicating artery (P<0.05). CONCLUSIONS In patients with unilateral ICA occlusion, the presence of collateral flow via the posterior communicating artery in the circle of Willis is associated with a low prevalence of border zone infarcts. Asymptomatic patients with an ICA occlusion do not have an increased collateral function of the circle of Willis.