Moyamoya Disease: New Predictors for Hemorrhagic Stroke Identified

Moyamoya disease, a rare progressive cerebrovascular disorder, carries a significant risk of stroke, even in individuals without prior symptoms. Recent research has focused on identifying factors that can predict which asymptomatic patients are most likely to experience a stroke, particularly the more dangerous hemorrhagic type.

Understanding Moyamoya Disease

Moyamoya disease is characterized by the narrowing of arteries at the base of the brain. As these arteries become blocked, the brain attempts to compensate by growing a network of tiny blood vessels – described as resembling a “puff of smoke” (moyamoya in Japanese) – to maintain blood flow. However, these newly formed vessels are often fragile and prone to rupture, leading to hemorrhagic stroke. While ischemic stroke (caused by restricted blood flow) is also a complication, hemorrhagic stroke represents a particularly severe and potentially life-threatening outcome.

Five-Year Stroke Risk in Asymptomatic Patients

A prospective cohort study, the Asymptomatic Moyamoya Registry in Japan, has been tracking patients with asymptomatic moyamoya disease to determine their long-term risk of stroke. Interim analysis of data collected between 2012 and 2015, following 103 patients (with 182 involved hemispheres) for five years, revealed a concerning stroke risk. The study, which continues to follow patients for a total of 10 years, found an annual stroke risk of 1.4% per person, 0.8% per hemisphere, and 1.0% per moyamoya hemisphere. This means that for any given hemisphere affected by asymptomatic moyamoya disease, there is a 1.0% chance of stroke occurring each year for the first five years.

Hemorrhagic Stroke Predominates

Of the seven strokes observed during the five-year follow-up period, six were hemorrhagic and only one was ischemic. This highlights the particularly dangerous nature of this condition, where the risk of bleeding in the brain is substantial even in the absence of prior stroke symptoms.

Predictors of Stroke Risk

Researchers identified specific radiological features that appear to increase the risk of stroke in asymptomatic patients. Specifically, a Grade-2 choroidal anastomosis – a particular pattern of blood vessel formation – was found to be an independent predictor of stroke, with a hazard ratio of 5.05 (95% CI, 1.24-20.6; P=0.023). This suggests that patients exhibiting this specific vascular pattern are at significantly higher risk. The presence of microbleeds, small areas of bleeding in the brain, also significantly predicted hemorrhagic stroke, with a hazard ratio of 4.89 (95% CI, 1.13-21.3; P=0.0342). Grade-2 choroidal anastomosis also significantly predicted hemorrhagic stroke with a hazard ratio of 7.05 (95% CI, 1.62-30.7; P=0.0093).

Hemodynamic Failure and Morphology

Current treatment for moyamoya disease focuses on flow augmentation, a procedure designed to improve blood flow to the brain. This approach is based on the understanding that hemodynamic failure – insufficient blood flow – is a dominant mechanism driving the disease. However, research suggests that the interplay between hemodynamic changes and morphological features (the structure of the blood vessels) is not fully understood and may influence long-term prognosis.

Who is Affected?

While originally described in Japan, moyamoya disease affects individuals worldwide. It can occur in both children and adults, although it is more frequently diagnosed in younger patients. Genetic factors are believed to play a role in the development of the disease, but the exact cause remains unclear.

Implications for Diagnosis and Management

The findings from the Asymptomatic Moyamoya Registry underscore the importance of careful monitoring of patients diagnosed with asymptomatic moyamoya disease. Identifying patients with Grade-2 choroidal anastomosis and microbleeds through imaging studies may help clinicians to prioritize those at highest risk for stroke and consider more aggressive interventions. Further research is needed to fully elucidate the mechanisms underlying stroke in moyamoya disease and to develop more effective strategies for prevention, and treatment.

As of February 5, 2026, ongoing research continues to investigate the long-term outcomes of patients enrolled in the Asymptomatic Moyamoya Registry, with follow-up extending to 10 years. This extended observation period will provide further insights into the natural history of the disease and the effectiveness of different management strategies.