gms | German Medical Science

Objective: Moyamoya disease (MMD) poses a unique cerebrovascular pathology characterized by progressive stenosis of the basal arteries of the circle of Willis with a network of fragile and dysfunctional vessels. Studies on the underlying pathophysiology and ultrastructural features of ex vivo vessel tissue are scarce in the literature. Hence, this study aimed at characterizing the ultrastructural phenotype of MMD vasculature via transmission electron microscopy (TEM).

Methods: Tissue samples of the middle cerebral artery (MCA) as well as superficial temporal artery (STA) during standard STA-MCA bypass operations were collected from a total number of n=7 MMD patients; specimens from patients with atherosclerotic vascular disease were used as the corresponding control. Tissue was fixed with 2.5 % glutaraldehyde in 0.1 M sodium cacodylate buffer and postfixed with 1 % osmium tetroxide and 0.8 % potassium ferrocyanide II in 0.1 M cacodylate buffer for 1.5 h, followed by dehydration in a graded ethanol series, and embedded in Epon resin. Semithin sections (0.5 µm) were cut and stained with methylene blue and azure II according to Richardson for light microscopy. Finally, ultrathin sections of 70 nm thickness were prepared using an ultramicrotome, collected on pioloform-coated copper grids subsequently stained with uranyl acetate, and examined with a Zeiss Leo 906 electron microscope at 80 kV acceleration voltage equipped with a slow scan 2K CCD camera.

Results: MMD samples showed distinct endothelial abnormalities with isoprismatic endothelial cells undergoing proliferation in the STA. Furthermore, the subendothelial layer was characterized by a marked collection of smooth muscle cells (SMCs) and fibrocytes (FCs), as well as heterogeneously disrupted elastic internal lamina. In the MCA, the vasculature also showed characteristic features with subendothelial thickening, accompanied by SMC and FC proliferation.

Conclusion: In this study, we shed light on ultrastructural vessel characteristics of ex vivo tissue from both intra- and extracranial vasculature in the same MMD patients via TEM. Both STA and MCA showed a heterogenous pattern of endothelial proliferation, intimal thickening with collection of SMCs, fibrocytes and collagen fibers, questioning the origin and migration patterns of these subendothelial cell structures in MMD.