Moyamoya is a progressive disease in which the walls of cerebral arteries around the Circle of Willis thicken, stenose, and occlude. It primarily affects the anterior circulation where progressive stenosis of the proximal carotid and middle cerebral arteries can cause ischemic symptoms and strokes.

As moyamoya disease begins to block cerebral arteries, tiny collateral vessels form to supply compensatory oxygen to the brain. These small vessels appear on an angiogram as puffs of smoke (moyamoya in Japanese), giving the disease its name. Oxygen deprivation from inadequate blood supply causes typical moyamoya symptoms such as paralysis of the feet, legs, or upper extremities, headaches, vision problems, and possible mental retardation.

The disease occurs worldwide. In children, it is characterized by the onset of one or more cerebral ischemic events. In adults, cerebral hemorrhages can occur.

Treatment Modalities

There are two primary treatment modalities for moyamoya, the first of which is indirect. Over the course of several procedures, a secondary scalp artery is rerouted onto the surface of the brain. From this artery, new blood vessels grow like roots into the brain, restoring blood flow to deprived brain tissues over the next three to six months. 

• During Encephaloduroarteriosynangiosis (EDAS), the healthy artery is sutured into an incision in the outermost protective covering of the brain.
• Pial synangiosis, a modification of EDAS, is when the healthy artery is sutured to the innermost protective covering of the brain.

The second treatment modality is direct surgical revascularization via an extracranial-intracranial (EC-IC) bypass. During this procedure, the superficial temporal artery (STA) is used as an extracranial bypass. It is cut and then connected to one or more of the intracranial cerebral arteries, typically the middle cerebral artery (MCA). This therapy is more commonly used in adults because their cerebral vessels are larger than those in children.

Cerebrovascular neurosurgeons use both therapies, indirect and direct revascularization, to meet the individual demands of a moyamoya patient. Dr. Fady T. Charbel, with the University of Illinois at Chicago, has found that, with a single bypass, the vessels will eventually occlude because blood flow is not well dispersed throughout the cerebral territories. He, therefore, prefers to anastomose the STA to two cerebral vessels (a double-barrel bypass) to augment flow to more than one territory with the bypass. He performs a side-to-side anastomosis of the STA to one cerebral artery branch and an end-to-side anastomosis of the STA to another cerebral artery branch. When feasible, he also augments his direct revascularization with indirect EDAS to further supplement cerebral flow.

REFERENCES

Charbel, Art and the logic of EC-IC Bypass; International Web-Based Neurosurgery Congress 2020

Lee M, et al, “Intraoperative blood flow analysis of direct revascularization in patients with moyamoya disease,” J Cereb Blood Flow Metab. 2011 Jan;31(1):262-74.