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
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.