Collateral configuration of the circle of Willis - Transcranial color-coded duplex ultrasonography and comparison with postmortem anatomy

Background and Purpose-The anterior communicating artery (AcoA) and posteri or communicating arteries (PcoA) of the circle of Willis provide the main r oute for collateral blood flow in cases of carotid artery obstruction. Tran scranial color-coded duplex ultrasonography (TCCD) allows real-time measure ment of the collateral function of the AcoA and PcoA. The primary objective of this study was to determine the collateral artery threshold diameters f or supplying collateral flow. Methods-In 12 acute stroke patients with a median age of 75 years (51 to 91 years), the collateral integrity of the circle of Willis as assessed by TC CD and carotid compression tests was compared with their postmortem anatomy . The lengths and diameters of the collateral arteries were measured. Results-TCCD demonstrated absent anterior collateral flow in 3 patients, In I of these patients, absence of anterior cross-flow was due to an occluded anterior cerebral artery, which was revealed at autopsy. Absent posterior collateral flow was found in 14 hemispheres. In 2 of these hemispheres, aut opsy revealed a fetal configuration of the posterior cerebral artery hamper ing posterior collateral flow. The median (range) diameters as found at aut opsy of the functional (n=19) and nonfunctional (n=16) collateral arteries of the circle of Willis were 1.1 (0.4 to 2.8) and 0.5 (0.3 to 0.7) mm, resp ectively (P=0.003), PcoA diameters were found to correlate negatively (rho= -0.50, P=0.01) to the diameters of their accessory P1 segments. Conclusions-The threshold diameter allowing for cross-flow through the prim ary collateral arteries of the circle of Willis is between 0.4 and 0.6 mm.