Pathogenesis of transient ischemic attacks within the vertebrobasilar arterial system.

Regional cerebral blood flow (rCBF) was measured by xenon 133 inhalation in 36 patients with vertebrobasilar arterial insufficiency (VBI), three patients with brain stem infarction, and 15 age-matched normal controls before and after inducing postural hypotension. Probes mounted over the suboccipital area by means of a helmet were used to measure rCBF over the brain stem and cerebellar regions. When lying flat, rCBF values measured over both cerebral hemispheres and the brain stem-cerebellar regions in patients with VBI were not significantly different from normal controls. Unlike carotid transient ischemic attacks, regional flow reduction rarely persisted for three weeks after transient ischemic symptoms in patients with VBI. When postural hypotension was induced, rCBF became significantly reduced in patients with VBI whether or not they were treated with papaverine. Dysautoregulation was restricted to vertebral, basilar, and posterior cerebral arterial distribution in patients with VBI of 1 to 12 months' duration, but was more widespread and involved both cerebral hemispheres in long-standing VBI. Hemodynamic factors and dysautoregulation appear to play a part in the pathogenesis of symptoms of VBI.