Moyamoya is a disease that involves the cerebral vasculature (arteries in the brain). It is progressive and results in occlusion (blockage) of the major arteries within the brain. These arteries form a structure known as the Circle of Willis.
A common presenting symptom that leads to the investigation and diagnosing of Moyamoya disease is a stroke or a transient ischemic attack (TIA). There are 2 types of stroke, hemorrhagic and ischemic.
“Moyamoya” is a Japanese word that means "puff of smoke". This description refers to the appearance that is seen in the abnormal vasculature and networks of collateral vessels next to the stenotic or occluded vessel during a cerebral angiogram. This appearance usually occurs on both sides of the brain but occasionally is only seen on one side.
“Moyamoya” affects the innermost wall of the blood vessels in the brain. This layer is known as the intima. The other layers within the blood vessels include the middle muscular layer known as the media and the outermost layer which is called the adventitia. Moyamoya disease has a characteristic pathological appearance when the affected vessels are examined under the microscope. The intima of the terminal portions of the internal carotid arteries is thickened. There is a wavy appearance of the internal elastic lamina. There is a thinning of the muscular media player. The proliferating intima layer may have deposits of lipids within it. The arteries coming off of the Circle of Willis may have varying degrees of involvement.
If not treated, usually with surgery, most people who have this disease will eventually have multiple strokes due to the continued occlusion of the arteries. This usually leads to a deterioration in mental status and physical function. Eventually, intracerebral bleeding can result in a hemorrhage and death. This is the reason that early diagnosis and surgical correction is crucial.
The genetics of Moyamoya disease are not fully understood. There is some suggestion that the disease is hereditary. Genetic research has found that in some families a gene called RNF213 has been associated with this disease. While the role of this gene is not fully understood, research has suggested that the protein the RNF213 gene codes for is involved in the development of blood vessels.
Although a specific genetic link has not been identified, individuals with Moyamoya disease have higher than normal levels of proteins that code for angiogenesis (proliferation of blood vessels) and tissue cell growth. The presence of these elevated levels of proteins may account for the thickening and proliferation of blood vessels characteristic of the disease.
Population studies on Moyamoya disease in Japan have found that approximately 15% of Japanese patients with this condition have family members that also have the disease. This indicates that there is likely some degree of genetic involvement. Genetic research indicates that the disease is likely autosomal dominant meaning that only one copy of the gene is required for a person to contract the disease. There is also an element of variable penetrance meaning that all individuals that have this condition are not affected with equal severity.
The medical treatment of Moyamoya disease has not been very effective. Medication is used primarily to decrease the risk of stroke and to treat the complications of stroke. antihypertensives are used to to maintain optimal blood pressure in order to prevent hemorrhagic stroke. If ischemic stroke is occurred, anticoagulants are used to prevent repeat ischemic events.
Therapy for Moyamoya Disease (Following a Stroke)
If someone has had a stroke, various forms of therapy including physical therapy, speech therapy and occupational therapy may be used. The needs of the patient will vary depending on the severity of the stroke.
Anticoagulation and Antiplatelet Therapy in Moyamoya Disease
Anticoagulation such as heparin, warfarin, and anti-platelet medications may be used depending on the severity of findings and the severity of the stroke. The physicians caring for the stroke patient will decide which is the best medication based on a risk-benefit analysis of multiple factors. However, these medications are not FDA approved specifically for the treatment of Moyamoya disease. The decision as to which medications to use, particularly in regard to the antiplatelet and anticoagulation therapy is best managed by a neurologist experienced in stroke prevention.
Prior to starting anticoagulation therapy, a CT is required to rule out a pre-existing intracranial hemorrhage.
Surgical Treatment for Moyamoya Disease:
It is preferable for person with Moyamoya disease to be treated before a stroke occurs. These individuals have a much better prognosis than those who have already had a stroke. The surgical treatments described below are preventative in that they are aimed at preventing a patient with Moyamoya disease from having a stroke in the first place.
Various surgical procedures have been used in the treatment of moyamoya disease, with the goal of revascularizing the ischemic hemisphere, including the following :
Several surgical procedures have been developed to treat Moyamoya disease. The surgical procedures are described as "direct anastomosis" or "indirect anastomosis". The direct anastomosis procedures directly revascularize a vessel while the indirect anastomosis procedures depend on the formation of collateral circulation to develop around the stenosis. Which procedures provides the best result has not been determined. There is, however sufficient evidence to conclude that the surgical revascularization does provide improved blood flow and clinically significant benefits.
In the direct anastomosis procedures, a branch from one of the arteries in the scalp is connected to one of the arteries on the outer surface of the brain. This provides immediate revascularization which improves blood flow to the brain.
Superficial temporal artery–middle cerebral artery (STA-MCA) anastomosis - In this direct anastomosis procedure a branch from one of the arteries in the scalp is connected to one of the arteries on the outer surface of the brain. This provides immediate revascularization which improves blood flow to the brain.
- Omental transplantation: - This is an indirect anastomosis procedure where part of the omentum (lining covering abdominal organs) is placed on the surface of the brain. The omentum is very rich and blood vessels. These vessels lead to new vessel growth that proliferates into the brain, improving blood supply to the brain.
- Encephalo-myo-synangiosis (EMS): In this indirect anastomosis procedure, the temporalis muscle is removed with its blood supply intact. The muscle is then placed (transposed) onto the surface of the brain in order to grow a new blood supply.
- Encephaloduroarteriomyosynangiosis (EDAMS): This is an indirect anastomosis procedure that uses a branch of the temporal artery. In this procedure, the branch off of the temporal artery is laid across the surface of the brain. It is then able to grow new blood vessels and form a new blood supply.
Patients undergoing one of the above surgical procedures will require approximately 3 days of postoperative hospitalization. After the normal minor scalp pain and occasional headaches, most patients have minimal pain. Following recovery from these surgeries, restrictions or minimal.
Early consultation with a neurologist is very important to document existing neurological deficits, address other medical issues, consider alternate diagnoses, and conduct appropriate testing to confirm the diagnosis of Moyamoya disease.
The neurologist will likely use multiple radiographic tests to evaluate and confirm the disease. A neuroradiologist can help recommend which test for most appropriate. Some of the test available include cerebral angiography and/or MR angiography.
Consultation with a neurosurgeon experienced in the surgical procedures described above can help plan the best surgical approach for a particular patient.
As described above, Moyamoya disease is a condition that usually affects the distal portions of both internal carotid arteries (bilateral) as well as the Circle of Willis which is the collection of intracerebral arteries supplying blood supply to the brain. However, in approximately 18% of patients, changes can only be seen on one side (unilateral findings). Over 50% of patients have radiologic findings in the posterior cerebral arteries as well as the internal carotid arteries.
The classic finding in Moyamoya disease is the "puff of smoke" appearance seen on cerebral angiography. This finding is due to the proliferation of abnormal small vessels which form a net-like network. When these fill with contrast dye during the angiography procedure, the "puff of smoke" appearance results. CT angiography and MR angiography is not always able to visualize this appearance due to the physics and flow rate of these radiologic methods.
Other findings that are common in Moyamoya disease include a generalized cerebral atrophy, collateral blood flow to the pia mater, prominent the medullary veins, multiple areas of micro-bleeds, and branches from the middle meningeal artery as well as other arteries supplying the dura crossing the dura mater.
There are six stages of severity in Moyamoya disease. These stages were first described by Suzuki and Takaku 1969. The progression proceeds from a narrowing of the "carotid fork" all the way to complete occlusion of the internal carotid artery. At that point, the blood supply to the brain is supplied by the external carotid artery. As the disease progresses, the "puff of smoke"appearance develops, intensifies, minimizes, decreases further, and then completely disappears. Once the internal carotid artery is completely occluded, the collateral blood flow causing the "puff of smoke" appearance disappears as well.
The key to effective treatment of Moyamoya disease is early diagnosis. If this disease is diagnosed early and effective surgical treatment implemented, patients with Moyamoya disease can have normal lifespans. The lifespan of patients that are diagnosed after having a stroke is largely dependent on the severity and number of strokes occurring prior to proper medical and surgical treatment. For those who have had strokes, significant mental deficits, physical deficits, and seizures are common.
In Moyamoya disease, establishing an early diagnosis and early surgical treatmentoffers the greatest chance to reduce the risk of ischemic stroke, hemorrhagic stroke, and neurological decline.
Moyamoya Disease: Dr. Fredric Meyer, a Mayo Clinic neurosurgeon discusses Moyamoya disease and what to look for when seeking care for Moyamoya disease
Moyamoya Disease Overview: Dr. John E. Wanebo