How is moyamoya disease characterized?

Updated: Nov 09, 2018
  • Author: Roy Sucholeiki, MD; Chief Editor: Amy Kao, MD  more...
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The term moyamoya (Japanese for "puff of smoke") refers to the appearance on angiography of abnormal vascular collateral networks that develop adjacent to the stenotic vessels. The steno-occlusive areas are usually bilateral, but unilateral involvement does not exclude the diagnosis. (See Workup.)

Blood vessel walls consist of 3 layers: the intima is the innermost layer; the media is a muscular middle layer; and the adventitia is the outermost layer. Separating the intima and media is the internal elastic lamina, an elastic membrane that is considered the outermost part of the intima. Pathologically, moyamoya disease is characterized by intimal thickening in the walls of the terminal portions of the internal carotid vessels bilaterally. The proliferating intima may contain lipid deposits. The anterior, middle, and posterior cerebral arteries that emanate from the circle of Willis may show varying degrees of stenosis or occlusion. This is associated with fibrocellular thickening of the intima, waving of the internal elastic lamina, and thinning of the media. (See Etiology, Workup, Treatment, and Medication.)

Numerous small vascular channels can be seen around the circle of Willis. These are perforators and anastomotic branches. The pia mater may also have reticular conglomerates of small vessels.

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