Natural history of endogenous collateral vessels after revascularization surgery in patients with moyamoya angiopathy

OBJECTIVE Moyamoya angiopathy (MMA) is characterized by the plasticity to develop endogenous collateral blood vessels to compensate for progressive steno-occlusion of proximal intracranial arteries. Bypass surgery has been anecdotally reported to induce regression of these collateral vessels, but a detailed analysis of their natural history is lacking. Here, the authors characterize these collaterals after bypass surgery. METHODS A single-center retrospective analysis of the medical records of 81 predominantly Caucasian MMA patients (121 hemispheres) treated with a combined superficial temporal artery–middle cerebral artery bypass and encephalodurosynangiosis between January 2011 and December 2021 was performed. Clinical data and longitudinal angiographic images were investigated to compare the development of different collateral types and to analyze the dependency between collateral vessels and bypass quality. RESULTS A total of 58 female and 23 male patients with a mean age of 41 ± 13.1 years at the time of first surgery were included. The majority of patients (92.6%) were European Caucasian. Ischemic events were the most common onset symptom (88.9%), followed by hemorrhage (11.1%). The mean follow-up time of digital subtraction angiography examinations was 19.8 ± 20.4 (range 0–108) months. Postoperatively, the majority of collateral vessels showed no changes over time. If changed, deep basal MMA collaterals as well as anterior leptomeningeal collaterals showed a consistent reduction over time, whereas posterior leptomeningeal collaterals, callosal collaterals, and extracranial-intracranial collaterals showed an increase more frequently (p < 0.006). Endogenous collateral vessels developed irrespective of bypass quality, while direct and indirect bypasses showed a synergistic development. CONCLUSIONS This study represents the first longitudinal angiographic characterization of endogenous collateral vessels in Caucasian MMA patients after combined bypass surgery. Collaterals within the region of the anterior circulation supplied by the bypass showed a consistent reduction over time. The development of collaterals depending on the presence and location of the bypass but not its quality indicates the individual endogenous need of moyamoya hemispheres as the determining factor and highlights the enduring plasticity and dynamic nature of the MMA collateral system over time.