Abstract
<b>Background and Objectives</b>
Vertebral artery hypoplasia (VAH) is an anatomical variation that may alter cerebral hemodynamics. The aim of this study was to first determine the prevalence of VAH in middle-aged and older adults. A second aim was to determine the impact of VAH on cerebral hemodynamics and brain volumes in a large sample of adults without cognitive impairment.
<b>Methods</b>
Participants underwent MRI scans to evaluate the internal carotid arteries, middle cerebral arteries, vertebral arteries (VAs), basilar artery, and posterior cerebral arteries (PCAs), and brain volumes. VAH was determined with 4D flow MRI scans using both diameter (<2.5 mm) and flow (<47 mL/min) of the VA. Brain volumes were determined from T1-weighted imaging.
<b>Results</b>
A total of 622 participants (66 ± 9 years; 391 female) were included, with 512 adults who were cognitively unimpaired (CN) and 110 who had cognitive impairment (C imp). The prevalence of VAH was 26% in CN adults and 33% in C imp adults. Within the CN group, we examined the cerebral hemodynamics and compared the adults with VAH (VAH+) with adults without VAH (No VAH). In the VAH+ group, the hypoplastic vertebral artery diameter was smaller (2.0 ± 0.2 mm vs 2.7 ± 0.5 mm; p < 0.001), blood flow was lower (29 ± 9 mL/min vs 102 ± 44 mL/min; p < 0.001), and pulsatility index was higher (1.9 ± 0.6 a.u. vs 1.3 ± 0.3 a.u.; p < 0.001) vs the contralateral vertebral artery. In the basilar artery, VAH+ had a smaller diameter (2.7 ± 0.4 mm vs 2.8 ± 0.3 mm; p = 0.040), lower blood flow (106 ± 34 mL/min vs 118 ± 37 mL/min; p <0.001), and higher pulsatility index (1.3 ± 0.3 a.u. vs 1.2 ± 0.3 a.u.; p = 0.035) compared with No VAH. PCA blood flow was lower in VAH+ compared with No VAH (49 ± 14 mL/min vs 53 ± 18 mL/min; p = 0.020), but there were no differences in diameter (p = 0.354) or pulsatility index (p = 0.109). VAH+ also had lower white matter volume compared with the No VAH group (411 ± 53 mL vs 425 ± 58 mL; p = 0.033).
<b>Discussion</b>
VAH prevalence is common with approximately 1 in 4 adults presenting with this anatomical variation. The presence of VAH was associated with impaired regional blood flow in the posterior circulation and elevated pulsatility in the basilar artery in cognitively unimpaired middle-aged and older adults.