Correlation of Xenon‐Enhanced Computed Tomography‐Defined Cerebral Blood Flow Reactivity and Collateral Flow Patterns

A chronic compromise of cerebral hemodynamics has been shown to identify a group of patients at an increased risk for stroke. Because a “steal phenomenon” induced by a vasodilatory challenge has characterized the group at greatest risk, it was hypothesized that these individuals would also have a severe compromise of primary collaterals and an increased dependence on leptomeningeal collaterals. Methods Twenty-three patients with symptomatic cerebrovascular disease underwent angiography and xenon-enhanced computed tomographic cerebral blood flow studies before and after 1 g IV acetazolamide within 6 months of each other. Cerebral blood flow vasoreactivity was classified by whether cerebral blood flow increased (>5%) or was unchanged (±5%) (group 1) or fell by >5% (group 2) in any vascular territory. Angiographic collateralization was classified into four types: normal (type 1), willisian (type 2), ophthalmic (type 3), and leptomeningeal (type 4). Results Twenty percent (2/10) of group 1 patients and 69% (9/13) of group 2 patients (P=.0009) had leptomeningeal collaterals. Conclusions A negative flow reactivity is significantly associated with a dependence on leptomeningeal collaterals and implies a state of maximal hemodynamic compromise.