Moyamoya Disease Surgery: Understanding the Risks and Potential Complications

Overview of Moyamoya Surgery and Its Inherent Risks

Moyamoya disease is a rare cerebrovascular disorder that often requires surgical intervention to restore proper blood flow to the brain. While revascularization surgery can be life-saving, it is considered one of the more complex and high-risk procedures in neurosurgery. Even when the operation proceeds smoothly, patients may still face significant postoperative complications. The delicate balance of cerebral circulation in moyamoya patients makes any surgical alteration potentially disruptive, leading to serious neurological consequences.

Understanding Cerebral Hyperperfusion Syndrome

One of the most critical risks following moyamoya surgery is cerebral hyperperfusion syndrome. In untreated moyamoya disease, the brain adapts to chronically reduced blood flow by developing collateral vessels—a fragile but stabilized network. When surgeons perform bypass procedures (such as EDAS or STA-MCA anastomosis), they introduce a sudden increase in blood flow from external sources. This abrupt change can overwhelm the previously underperfused brain tissue, leading to excessive pressure within the cerebral vasculature.

This condition may result in intracranial hemorrhage, especially in patients with long-standing ischemia. Moreover, the rapid shift in hemodynamics can trigger edema, seizures, or even stroke-like symptoms despite successful revascularization. Monitoring blood pressure closely in the postoperative period is essential to mitigate this risk.

Common Post-Surgical Complications

Bleeding and ischemic events are among the most frequently observed complications after moyamoya surgery. Although hemorrhage is a feared outcome, ischemic stroke remains more common, particularly due to shifts in cerebral blood distribution. The introduction of new blood flow pathways can inadvertently "steal" circulation from other vulnerable regions of the brain—a phenomenon known as vascular steal syndrome—leading to infarction in areas that were previously stable.

These infarcts may occur either at the surgical site or in remote but already compromised regions of the brain, emphasizing the importance of meticulous preoperative planning and intraoperative neuromonitoring.

Long-Term Challenges: Graft Failure and Microvascular Occlusion

Another concern is the durability of the surgical bypass. While intraoperative imaging may confirm immediate patency of the graft, microvascular thrombosis can develop days or weeks later, especially in pediatric patients or those with underlying endothelial dysfunction. Small vessel occlusion can compromise the long-term success of the procedure, resulting in suboptimal revascularization and persistent risk of stroke.

Follow-up imaging, such as MRI, MRA, or perfusion studies, is crucial for assessing graft function and detecting early signs of failure. Some patients may require secondary interventions if collateral development is insufficient.

Conclusion: Weighing Benefits Against Surgical Risks

While moyamoya surgery offers significant benefits in reducing stroke risk and improving quality of life, it is not without dangers. A thorough understanding of potential complications—including hyperperfusion, ischemia, hemorrhage, and graft failure—is vital for both clinicians and patients. Multidisciplinary care involving neurosurgeons, neurologists, and intensive care specialists enhances outcomes and supports safer recovery. With careful patient selection, advanced monitoring techniques, and personalized postoperative management, many of these risks can be minimized.