Moyamoya disease

Moyamoya disease 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. Hemorrhagic events can also occur. The condition leads to irreversible blockage of the carotid arteries 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 (TIAs or "mini strokes"), sensorimotor paralysis (numbness in the extremities), 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 it is important to recognize these lesions and treat them early on. Without treatment, there is progressive deterioration of neurologic function and re-hemorrhage.

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Diagnosis

The diagnosis is initially suggested by CT, MRI, or angiogram. In fact, the name derives from its angiographic image; the "puff of smoke," which is how moyamoya loosely translates from Japanese, refers to the appearance of multiple compensatorily dilated striate vessels seen on angiography. 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.

Treatment

There are many operations that have been developed for the condition, but currently the most favored are the in-direct procedures EDAS, EMS, and multiple burr holes and the direct procedure STA-MCA. Direct superficial temporal artery (STA) to middle cerebral artery (MCA) 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 lobes 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) procedure, 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.

In the multiple burr holes procedure, multiple small holes (burr holes) are placed in the skull to allow for growth of new vessels into the brain from the scalp.

In the STA-MCA procedure, the scalp artery (superficial temporal artery or STA) is directly sutured to an artery on the surface of the brain (middle cerebral artery or MCA). This procedure is also commonly referred to as an EC-IC (External Carotid-Internal Carotid) bypass.

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 cerebral blood flow (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 children being treated for Moyamoya as the type of anesthesia they require is very different from the standard anesthetic children get for almost any other type of neurosurgical procedure.

Prognosis

The long term outlook for patients with treated Moyamoya seems to be good. While symptoms may seem to improve almost immediately after the in-direct EDAS, EMS, and multiple burr holes surgeries, it will take probably 6-12 months before new vessels (blood supply) can develop sufficiently. With the direct STA-MCA surgery, increased blood supply is immediate.

Once major strokes or bleeding take place, even with treatment, the patient may be left with permanent loss of function so it is very important to treat this condition promptly.

References

• http://www.moyamoya.com