Use of Quantitative Magnetic Resonance Angiography to Stratify Stroke Risk in Symptomatic Vertebrobasilar Disease

Abstract

Conclusion: Quantitative magnetic resonance angiography (QMRA) can stratify risk for stroke in patients with symptomatic vertebrobasilar disease (VBD). Summary: Phase-contrast QMRA is a magnetic resonance technique for noninvasively measuring blood flow in intracranial vessels (Magn Reson Imaging 2000;18:697-706). The authors used a standard protocol that included QMRA to evaluate patients with symptomatic VBD. QMRA was used to stratify patients according to the presence or absence of flow compromise distal to the site of VBD. Flow was considered compromised in specific vessels if it was reduced greater than 20% of the lower limit of normal baseline value for that vessel. Flow compromise was evaluated in the basilar and posterior cerebral arteries. The basilar artery was designated as having reduced flow if flow measurements were less than 12 mL/min, and the posterior cerebral arteries were designated as having reduced flow if flow measurements were less than 40 mL/min. Patients with low distal flows were then offered either surgical or endovascular intervention, and other patients received standard medical therapy. The article reports the results of this protocol for patients treated from 1998 to 2003. There were 50 patients subjected to the protocol and 47 available for follow-up over a mean interval of 28 months. Kaplan-Meier curves were used to calculate stroke and stroke-free survival at 2 years and a combination of stroke-free survival and freedom from transient ischemic attacks at 2 years. Patients with normal distal flow (n = 31) had event-free survivals of 100% and 96%, respectively. At 2 years patients with low distal flows had a 71% event-free survival with respect to stroke and a 53% event-free survival with respect to the combined end point of stroke and transient ischemic attack. Patients with low distal flows had a higher risk of recurrent ischemia (P = .003). Twelve patients with low flow underwent treatment and had 82% event-free survival. With Cox proportional analysis, flow status effected event-free survival independently of covariants. Comment: Patients with symptomatic VBD can be offered intervention for large-vessel stenoses that are believed to be hemodynamically significant. However, collateralization in the posterior circulation can be extensive, and the presence of hemodynamically significant lesions in the proximal vessels does not necessarily result in diminished posterior circulation blood flow. QMRA may provide a method of selection for intervention for those patients with VBD who are most likely to benefit from an open or endovascular surgical procedure. This article may represent a major step forward for the selection of patients for vertebral artery reconstruction.