Preoperative embolization of the external carotid artery branches as an adjunct to superficial temporal artery-to-middle cerebral artery bypass

When technically feasible, the preferred revascularization procedure in patients with adult moyamoya disease is a superficial temporal artery-to-middle cerebral artery (STA-MCA) bypass. The caliber of the STA has been reported as a prognostic factor for a successful bypass, with smaller-caliber STA being more likely to fail. We describe a novel approach to this circumstance in which preoperative embolization of external carotid artery (ECA) branches is used to augment blood flow through a small STA as a prelude to bypass surgery. We report 2 cases: a 42-year-old female presenting with symptomatic ischemic and radiographically progressive moyamoya disease and a 23-year-old female presenting with advanced moyamoya disease secondary to diabetes. Preoperative angiography demonstrated small-caliber STAs in each case, and primary revascularization was deemed difficult. Preoperative ECA embolization was undertaken to shunt blood toward the STA, thereby increasing its flow and caliber. In both cases, angiography after embolization demonstrated a 20%-45% increase in STA size, and doppler ultrasound indicated a 14%-50% increase in flow. Subsequently, both patients underwent successful STA-MCA bypass combined with encephalomyosynangiosis without complications. Of 167 STA-MCA bypasses performed by the senior author, embolization was performed in 7 unique patients on 9 sides. ECA embolization may be a beneficial adjunct when considering a direct bypass in the setting of a small STA. It can increase blood flow through the STA, making the operation technically easier and enhancing the patency of the bypass.