THE ANATOMY OF THE POSTERIOR COMMUNICATING ARTERY AS A RISK FACTOR FOR ISCHEMIC CEREBRAL INFARCTION

Background. After the occlusion of an internal carotid artery the prin cipal source of collateral flow is through the arteries of the circle of Willis, but the size and patency of these arteries are quite variab le. Study of the anatomy of the collateral pathways in patients with i nternal-carotid-artery occlusion with or without infarction in the wat ershed area of the deep white matter may identify patterns that afford protection from ischemic infarction. Methods. Using conventional magn etic resonance imaging and three-dimensional phase-contrast magnetic r esonance angiography, we evaluated 29 consecutive patients (32 hemisph eres at risk) with angiographically proved occlusion of the internal c arotid artery. Four collateral pathways to the occluded vessel were ev aluated: the proximal segment of the anterior cerebral artery, the pos terior communicating artery, the ophthalmic artery, and leptomeningeal collateral vessels from the posterior cerebral artery. Results. Only features of the ipsilateral posterior communicating artery were relate d to the risk of watershed infarction. The presence of posterior commu nicating arteries measuring at least 1 mm in diameter was associated w ith the absence of watershed infarction (13 hemispheres, no infarcts; P < 0.001). Conversely, there were 4 water-shed infarcts in the 6 hemi spheres with posterior communicating arteries measuring less than 1 mm in dimeter and 10 infarcts in the 13 hemispheres with no detectable f low in the ipsilateral posterior communicating artery. Conculsions. A small (< 1 mm in diameter) or absent ipsilateral posterior communicati ng artery is a risk factor for ischemic cerebral infarction in patient s with internal-carotid-artery occlusion.