Influence of the collateral function of the circle of Willis on hemispherical perfusion during carotid occlusion as assessed by transcranial colour-coded duplex ultrasonography

Objectives: to investigate the collateral potential of the circle of Willis with transcranial colour-coded duplex ultrasonography and common carotid a rtery (CCA) compression. Materials and methods: in 46 atherosclerotic patients without cerebrovascul ar disease, the functional potency of the collaterals of the circle of Will is, the anterior and posterior communicating arteries, was assessed. The Pe ak Systolic Velocity (PSV) decrease in the middle cerebral artery (MCA) dur ing CCA compression between complete and incomplete circles was compared. Results: in 10 (22%) patients a complete and in 36 (78%) patients an incomp lete circle of Willis was found, mainly dire to non-functioning posterior c ommunicating arteries. In hemispheres with collateral supply through both t he anterior and the posterior communicating artery, the median PSV decrease in the MCA during CCA compression was 43%. When the posterior, anterior or both communicating arteries (I hemisphere) were missing the PSV decrease w as 58% (p = 0.003), 70% (p = 0.001) and 75%, respectively. Conclusions: collateral flow from the basilar to the carotid territory is o ften hampered by non-functioning posterior communicating arteries. A non-fu nctioning anterior communicating artery is rare. A complete collateral circ ulation provides better perfusion of the MCA during carotid occlusion as co mpared with collateral supply through only the anterior or the posterior co mmunicating artery in the case of an incomplete circle of Willis.