Moyamoya disease is a rare disorder characterized by luminal stenosis secondary to intimal thickening and smooth muscle cell proliferation of the distal internal carotid arteries and the main branches of the circle of Willis. An aberrant, compensatory network of blood vessels develops to maintain collateral circulation to brain tissue. This pathophysiological process leads to a characteristic "puff of smoke" appearance on angiographic studies.
Although moyamoya disease occurs in people of all ages, it typically affects children and adults under the age of 50. It can be difficult to diagnose and can cause recurring transient ischemic attacks (TIAs), strokes, seizures and cognitive deterioration.
As a center of expertise for cerebral microvascular surgery, Mayo Clinic has a distinguished history of treating moyamoya disease. Neurosurgeons at Mayo Clinic in Phoenix/Scottsdale, Arizona, are pioneering new approaches to treatment, to improve cerebral perfusion with the goal of eliminating or reducing complications of the disease.
"While moyamoya disease is rare overall, it's probably underdiagnosed," says Bernard R. Bendok, M.D., chair of Neurosurgery at Mayo Clinic's campus in Arizona. "It's an important cause of stroke in young people. Because of the associated complications, the impact per case is high."
Diagnosis of moyamoya disease requires an angiogram, which is not always routinely performed after stroke or TIA. However, MRI and CT, which are generally done after stroke or TIA, can provide subtle signs of moyamoya disease, indicating the need for an angiogram.
Dr. Bendok, who has treated moyamoya disease for 20 years, notes that narrowing of the carotid arteries shown on MRI and CT might be assumed to indicate atherosclerosis. "But it could be moyamoya disease," he says. "In atherosclerosis, the narrowing of the carotids tends to be irregular, whereas it's typically smoother in moyamoya disease and, more often than not, bilateral."
At Mayo Clinic, perfusion studies are performed before treatment for moyamoya disease to obtain an objective endpoint for improving vascularization. In addition, cognitive testing and quality-of-life measurement are done before and after treatment.
Treatment of moyamoya disease generally focuses on preventing stroke. "However, stroke prevention is just the tip of the iceberg," Dr. Bendok says. "Preventing hemorrhage is an important consideration, and managing associated aneurysms surgically or with endovascular treatments could be another issue. It's also critical to pay attention to the fact that hypoperfusion can reduce cognitive abilities, and improved perfusion can reverse that decline."
The preferred surgical approach to treatment of moyamoya disease — direct or indirect bypass — has been controversial. "Our approach is always to do an indirect bypass. We often add a direct bypass if the anatomy is favorable, especially when the patient has progressive symptoms related to hypoperfusion."
Typically, revascularization treatment involves the middle cerebral artery distribution. At Mayo Clinic's campus in Arizona, "we have pioneered the approach of adding pericranial grafts to the anterior cerebral artery distribution, which further enhances blood flow to the hemisphere," Dr. Bendok says.
To avoid complications during revascularization, Dr. Bendok and colleagues have introduced awake surgery for treatment of moyamoya disease and other cerebral vascular conditions.
"Awake surgery is the best form of neuromonitoring," Dr. Bendok says. "If the patient experiences a symptom during surgery, we can quickly increase the patient's blood pressure." Patients are kept hypertensive during neurovascular awake surgery procedures, and contralateral motor movements are periodically evaluated. No episodes of significant blood pressure fluctuations have occurred and no adverse events have been noted. The postoperative course for the patients has been uneventful, without new or worsening deficits.
Dr. Bendok's commitment to improving perfusion began early in his career when he treated a young woman with moyamoya disease. She was nearly unresponsive at presentation due to poor brain perfusion. Sometime later, after giving a talk on moyamoya disease at a hospital, Dr. Bendok was approached by an audience member — his former patient, who was working in the hospital's coding and billing department.
"After her treatment she was able to earn an associate degree," Dr. Bendok says. "That experience was a powerful demonstration to me of the fact that you can help people by improving brain perfusion."