What is Moyamoya Disease?

Moyamoya is an extremely rare disorder in most parts of the world except in Japan. The pathogenesis of Moyamoya disease is unknown. Moyamoya disease is characterized by progressive intracranial vascular stenoses of the circle of Willis, resulting in successive ischemic events. The condition leads to irreversible blockage of the main blood vessels to the brain as they enter into the skull. It is a disease that tends to affect children and adults in the third to fourth decades of life. In children it tends to cause strokes or seizures. In adults it tends to cause bleeding or strokes. The clinical features are cerebral ischaemia (strokes), recurrent transient ischaemic attacks (TIA's or "mini strokes"), sensorimotor paralysis (numbness in the extremeties), convulsions and/or migraine-like headaches.

The process of blockage (vascular occlusion) once it begins tends to continue despite any known medical management unless treated with surgery. The repeated strokes can lead to severe functional impairment or even death so that it is important to recognize these lesions and treat them early on. Without treatment, there is progressive deterioration of neurologic function and re-hemorrhage.

The diagnosis is initially suggested by CT or MRI. Contrast-enhanced T1-weighted images are better than FLAIR images for depicting the leptomeningeal ivy sign in moyamoya disease. MRI and MRA should be performed for the diagnosis and follow-up of moyamoya disease. Diffusion-weighted imaging can also be used for following the clinical course of children with moyamoya disease, in whom new focal deficits are highly suspicious of new infarcts.

Often nuclear medicine studies such as SPECT (single photon emission computerized tomography) are used to demonstrate the decreased blood and oxygen supply to areas of the brain involved with the Moyamoya disease. Conventional angiography provided the conclusive diagnosis of moyamoya disease in most cases and should be performed before any surgical considerations.

There are many operations that have been developed for the condition, but currently the most favored are: EDAS, EMS, STA-MCA and multiple burr holes. Direct superficial temporal artery to middle cerebral artery bypass is considered the treatment of choice, although it's efficacy, particularly for hemorrhagic disease, remains uncertain. Multiple burr holes have been used in frontal and parietal bones with good neovascularisation achieved.

The EDAS (encephaloduroarteriosynangiosis) procedure requires dissection of a scalp artery over a course of several inches and then making a small temporary opening in the skull directly beneath the artery. The artery is then sutured to the surface of the brain and the bone replaced.

In the EMS (encephalomyosynangiosis) operation, the temporalis muscle, which is in the temple region of the forehead, is dissected and through an opening in the skull placed onto the surface of the brain.

All of these operations have in common the concept of a blood and oxygen "starved" brain reaching out to grasp and develop new and more efficient means of bringing blood to the brain and bypassing the areas of blockage. The modified direct anastomosis and encephalo-myo-arterio-synagiosis play a role in this improvement by increasing CBF after the operation. A significant correlation is found between the postoperative effect and the stages of preoperative angiograms. It is crucial for surgery that the anesthesiologist have experience in managing these children as the type of anesthesia they require is very different from the standard anesthetic children get for almost any other type of neurosurgical procedure.

The long term outlook for children with treated Moyamoya seems to be good. While symptoms may seem to improve almost immediately after surgery, it will take probably 6-12 months before new vessels can develop sufficiently. Once major strokes or bleeding take place, even with treatment the child may be left with permanent loss of function so it is very important to treat this condition promptly.