Flow Evaluation of STA-MCA Bypass Using Quantitative Ultrasonography: an Alternative to Standard Angiography for Follow Up of Bypass Graft

Purpose: To date, digital subtraction angiography (DSA) has been considered as the gold imaging modality for assessing graft patency after extracranial-intracranial bypass. The utility of a noninvasive and quantitative method of assessing graft flow postoperatively was evaluated by using quantitative ultrasonography. Method: All STA-MCA bypass surgery performed over a 5-year period at a single institution were reviewed. Measured by duplex ultrasonography, pre-operative (day1) and post-operative (day1, day7, 3month and 6 month) graft blood flow rates were recorded and analyzed. Results were correlated to Matsushima grade determined by DSA performed within 24 h when ultrasonography was conducted to confirm the graft function. Results: 100 patients with 131 operated hemispheres were included in this study. The mean flow rates in the STA graft on pre-operative day1, post-operative day 1 and 7, at 3- and 6-month postoperatively were 24.1, 106.7, 112.6, 97.4 and 79.7 ml/min respectively. The mean post-operative flow in the STA graft graded as A/B/C were significantly different (168.0 +/- 34.8 ml/min, 91.0 +/- 15.5, 42.1 +/- 17.2 ml/min, respectively, p = 0.000). 124.5 ml/min and 65.5 ml/min are good cut-off value for predicting post-operative graft Matsushima grade. The analysis also showed excellent agreement between ultrasonography and DSA for assessing bypass function (kappa = 0.78). Conclusions: The patency of the STA grafts can be assessed noninvasively by quantitative ultrasonography, which results are comparable to those of conventional DSA. This, therefore, suggest that quantitative ultrasonography may be an alternative method to standard DSA for serial follow up of STA grafts.