Posterior communicating artery variation is linked to compromised cerebral hemodynamics in middle-aged and older adults

We investigate whether common circle of Willis (CoW) variants relate to cerebral blood flow (CBF) characteristics among aging adults. Vanderbilt Memory and Aging Project participants free of clinical stroke (<i>n</i> = 390, 71 ± 8 years, 55% male) completed magnetic resonance angiography to assess cerebral artery variants and pseudocontinuous arterial spin labeling to quantify resting CBF and spatial coefficient of variation (sCoV), a marker of perfusion heterogeneity or stability. Linear regression models related categorical variants to regional CBF and sCoV, adjusting for age, sex, race/ethnicity, education, cognitive status, Framingham Stroke Risk Profile, and <i>APOE</i>-ε4 status. Absence of at least one posterior communicating artery (PcoA) related to lower occipital lobe CBF (<i>p</i> = 0.001) and higher global (<i>p</i> = 0.003), temporal (<i>p</i> = 0.001), and occipital lobe sCoV (<i>p</i> = 0.01). Bilateral PcoA absence related to lower global (<i>p</i> = 0.01), parietal (<i>p</i> = 0.01), and occipital lobe CBF (<i>p</i> = 0.0001) and higher global (<i>p</i> < 0.0001), temporal (<i>p</i> < 0.0001), and occipital lobe sCoV (<i>p</i> = 0.0003). Hypoplastic and fetal-type variants did not relate to outcomes (<i>p</i> > 0.22). Findings demonstrate that missing PcoAs influence both perfusion magnitude and efficiency, suggesting that common CoW variants may produce regionally coherent hemodynamic effects in heart-healthy aging adults and represent markers of early cerebrovascular vulnerability.