Introduction: Moya moya disease (MMD) is characterized by progressive stenotic occlusion of the distal internal carotid arteries (ICA) and proximal anterior and middle cerebral arteries. Despite several associated conditions described, the exact aetiology of MMD has not been elucidated. The authors investigated if MMD could be caused exclusively by mechanical stresses induced by blood flow against a susceptible intracranial vasculature.
Methods: The pre-operative digital subtraction angiography (DSA) images of 54 patients diagnosed with MMD were reviewed. The angle subtended by the horizontal cavernous segment of the ICA and the supraclinoid segment (CAV-SCL angle) of the ICA in lateral view angiograms was measured and compared with age-matched controls.
The DSA image of the ICA from the cervical segment to the bifurcation into the anterior and middle cerebral arteries of a control subject was extracted. The (CAV-SCL angle) of the ICA in true lateral view was progressively increased using a software, to obtain four models of increasing angles viz. original, 600, 900 and 1100. The models were subjected to simulated blood flow studies using computational fluid dynamics (CFD) methodology.
Results: The (CAV-SCL angle) of the ICA was greater in MMD patients compared to controls. The CFD methodology simulated blood flow in the ICA model. As the CAV-SCL angle was progressively increased, the wall shear stress increased in the vicinity of the ICA bifurcation. The high wall shear stress induces the formation of endothelial cushions. Erratic cushion formation acting on a ‘swaying’ supraclinoid ICA and hemodynamic disruption of the internal elastic lamina causing changes in the tunica media could account for the pathogenesis of MMD.
Conclusions: Moya moya disease occurs in the setting of a unique interplay of mechanical factors acting on a susceptible weak vasculature. The ‘Mechanical Theory’ of Moya moya disease could explain the pathogenesis of this enigmatic disease.
Patient Care: The etiopathogenesis of Moyamoya disease is unknown. The work submitted proposes a novel theory of the pathogenesis of Moyamoya disease. This theory could explain the clinical, radiological and histopathological features of the disease. Research could thus be focussed towards finding a solution for developing preventive and therapeutic strategies for Moyamoya disease.
Learning Objectives: By the conclusion of this session, participants should be able to
1. Describe the anatomical characteristics of intracranial vasculature unique to Moya moya disease.
2. Understand the hemodynamics of Moya moya disease using computational fluid dynamics
3. Discuss a novel theory of pathogenesis of Moya moya disease; Moya moya disease is caused by hemodynamic mechanical factors acting on susceptible vasculature.