Moyamoya Disease pathophysiology in adults
Moyamoya disease is a rare, progressive cerebrovascular disorder characterized by the stenosis or occlusion of the terminal portions of the internal carotid arteries and their proximal branches. While it is often diagnosed in children, adults can also be affected, and the disease’s pathophysiology in this population presents unique features that influence clinical presentation and management strategies. Understanding the underlying mechanisms in adults is crucial for accurate diagnosis and optimal treatment.
At the core of moyamoya disease in adults is a process of abnormal vascular remodeling within the cerebral circulatory system. The disease begins with progressive intimal thickening, which leads to narrowing of the distal internal carotid arteries and their main branches, including the anterior cerebral artery and middle cerebral artery. This narrowing is believed to result from proliferative changes in the intimal layer of the arteries, possibly driven by genetic, environmental, or immune-mediated factors. Unlike atherosclerosis, which involves lipid accumulation and plaque formation, moyamoya’s thickening is characterized by smooth muscle cell proliferation and extracellular matrix deposition, leading to a diffuse stenosis.
As the primary arteries become increasingly stenotic, cerebral blood flow (CBF) is compromised, especially in the regions supplied by the affected arteries. To compensate for reduced perfusion, the brain initiates the development of a network of abnormal collateral vessels. These vessels are typically small, fragile, and convoluted, resembling a “puff of smoke” on angiographic imaging—hence the name “moyamoya,” which means “hazy” or “puff of smoke” in Japanese. These collateral pathways include dilated leptomeningeal anastomoses, perforating arteries, and small transdural collaterals from external carotid artery branches.
The formation of these abnormal vessels is a double-edged sword. While they initially serve as compensatory mechanisms to sustain cerebral perfusion, they are often insufficient and prone to rupture, leading to hemorrhagic strokes. Additionally, the fragile nature of these vessels can cause ischemic events, such as transient ischemic attacks or strokes, especially during episodes of hypoperfusion or hemodynamic stress.
In adults, the disease also tends to have a different clinical course compared to children. Adults are more likely to present with hemorrhagic strokes due to rupture of the fragile collateral vessels, whereas children more commonly experience ischemic events. This difference reflects the varying balance between ischemia and hemorrhage in the disease’s progression.
From a molecular perspective, the pathophysiology of moyamoya involves complex genetic and signaling pathways. Certain genetic mutations, particularly in the RNF213 gene, have been identified as significant risk factors, especially in East Asian populations. These genetic factors may influence vascular cell proliferation, apoptosis, and remodeling processes, contributing to the characteristic arterial stenosis and abnormal collateral formation.
In conclusion, the pathophysiology of moyamoya disease in adults revolves around progressive arterial stenosis driven by proliferative intimal changes, compensated by the development of abnormal collateral vasculature. This process results in a delicate balance between ischemia and hemorrhage, shaping the clinical spectrum and informing management approaches. A thorough understanding of these mechanisms is essential for clinicians to diagnose early, assess risks, and tailor treatment strategies effectively.