The purpose of this study was to compare the effects of critical neck angulation (rotation and hyperextension) on vertebral artery perfusion in symptomatic and control populations and to determine whether this represents a risk factor for ischemic stroke. In a cross-sectional study, 64 symptomatic individuals with well-documented brainstem ischemic events (average age, 70.9 yr) and 37 control subjects (average age, 66.3 yr) were evaluated using a dynamic magnetic resonance angiography technique designed to mimic activities of daily living. Abnormalities of perfusion at the atlantoaxial and atlantooccipital junction and distal vertebral artery were recorded and scored independently by two neuroradiologists. Volume flow analysis was also recorded at the basilar artery, and distal and proximal vertebral arteries. Symptomatic subjects displayed a consistent pattern (56.4%) of contralateral hypoperfusion at the atlantoaxial and atlantooccipital junction and distal segments (grades 3 and 4) (p < 0.001). Unsuspected hypoplasia was noted in 13% of the symptomatic subjects with a right-sided preponderance (88%), suggesting developmental susceptibility. Occlusion was noted in all subjects with contralateral neck rotation. Postpositional ischemia was present (68%) and correlated with female gender (p < 0.001), severity of stenosis (p < 0.001), vascular risk factors (p < 0.001), and microinfarction on magnetic resonance images (p < 0.05). Flow analysis showed low basilar artery perfusion (< 25 ml/min) in 63.6%, and unsuspected steal with neck motion in 4 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

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Although no harmful effects were reported in 1023 cases, an unexpected high rate of 14% of individuals experienced sensory stimulation in both 3 T and 1.5 T units. Females appear to be more magnetically sensitive.