Evaluation of extracranial-intracranial arterial bypass function with magnetic resonance angiography

Extracranial-intracranial (EC/IC) arterial bypass surgery is a valuable therapeutic modality in the field of cerebrovascular surgery. The assessment of bypass patency and its functional parameters are of utmost importance in the postoperative course. The present study examined the potential role of quantitative MR-based volume flow measurement techniques for the investigation of bypass patency. Forty-one patients with steno-occlusive cerebrovascular disease treated with EC/IC bypass surgery underwent conventional angiographic (CA) and two-dimensional cine-phase MR-based angiographic assessment (MRA) of bypass function. CA bypass function was evaluated as poor (grade I), moderate (grade II), or extensive (grade III) and was compared with quantitative volume flow measurements (BVF) obtained in MRA studies. Bypass filling was classified as grade I in 15% of the cases, grade II and grade III in 36% and 49% of the studies, respectively. Mean BVF differed significantly in the different grades: 31.9 +/- 9.8 ml/min in grade I, 73.6 +/- 16.7 ml/min in grade II, and 97.2 +/- 26.6 ml/min in grade III. BVF values of 48 ml/min or lower (n = 6) were specific for grade I bypass function, while only BVF values higher than 111 ml/min (3/20, 15%) are specific for extensive angiographic bypass function. The assessment of EC/IC bypass patency with quantitative BVF measurements provides exact, investigator-independent information under physiological conditions. MRA is well correlated with the angiographic bypass grading system.