Background The Circle of Willis (CoW) is comprised of seven arterial segments forming the main circulatory anastomosis distributing cerebral blood flow (CBF). The circle plays an essential role in both collateral circulation and as a pressure diffuser to protect downstream microvasculature from injury. Given that fully patent circles are uncommon and communicating arteries are the most commonly missing segments, this study examined their potential physiological significance. We investigate if missing the smallest CoW segments, including the anterior communicating artery (AcoA) and the posterior communicating arteries (PcoAs), relates to regional CBF alterations.
Methods Vanderbilt Memory & Aging Project participants free of clinical stroke and dementia were studied (n= 314, 73±7 years, 58% male). Multimodal 3T brain MRI included magnetic resonance angiography (MRA) for examining the CoW patency and psuedo-=continuous arterial spin labeling for quantifying resting CBF (mL/100g/min) for the frontal, temporal, parietal, and occipital lobes. Using MRA, the AcoA and two PcoA segments were manually coded as present or absent by a board-certified neuroradiologist. Linear regressions related AcoA and PcoA variants to CBF regions of interest (ROIs), adjusting for age, sex, race/ethnicity, education, Framingham Stroke Risk Profile, diagnosis, apolipoprotein E4 (APOE4) status, and ROI tissue volume.
Results Missing at least one PcoA segment was prevalent in 37% of the cohort while a missing AcoA segment was prevalent in 9%. Missing at least one PcoA segment related to lower temporal lobe CBF (b=-2.11, p=0.03) but not frontal, parietal, or occipital CBF (p-values>0.07). A missing AcoA segment did not relate to any lobar CBF (p-values>0.05).
Conclusions Our results suggest that missing a PcoA segment appears to have regional associations with temporal lobe CBF, possibly reflecting early hemodynamic compromise that can result in subsequent microvascular damage to downstream tissue. In contrast, a missing AcoA did not relate to CBF. Unique CoW variations may be detrimental to brain health and further research is warranted to examine their clinical significance, including the impact of regional CBF changes on cognitive functions mediated by the temporal lobes.