Nishimoto and Takeuchi reported on 111 cases that were selected on the basis of the two main radiologic criteria. The condition was observed mainly in infants, children, and adolescents (more than half the patients were younger than 10 years of age, and only 4 were older than age 40 years). All of their patients were Japanese, in whom the disease seems disproportionately prevalent; both males and females were affected, and 8 were siblings. The symptom that led to medical examination was usually a sudden weakness of an arm, leg, or both on one side. The symptoms tended to clear rapidly but recurred in some instances. Headache, convulsions, impaired mental clarity, visual disturbance, and nystagmus were less frequent. In older patients, subarachnoid hemorrhage was the most common initial manifestation. Other symptoms and signs were speech disturbance, sensory impairment, involuntary movements, and unsteady gait. Characteristics noted in other series have included prolonged TIAs (this accords with our experience), characteristically induced by hyperventilation or hyperthermia, parenchymal rather than subarachnoid hemorrhages (most situated in the basal ganglia or thalamus), and an unusual “rebuildup” EEG phenomenon in which high-voltage slow waves reappear 5 min after the end of hyperventilation.
Postmortem examinations of cases of moyamoya have yielded a reasonably clear picture of the intracranial distal carotid lesion. The adventitia, media, and internal elastic laminae of the stenotic or occluded arteries were normal, but the intima was greatly thickened by fibrous tissue. No inflammatory cells or atheromata were seen. In a few cases, hypoplasia of the vessel with absent muscularis has been described. The profuse rete mirabile consists of a fine network of vessels over the basal surface of the brain (in the pia-arachnoid), which, according to Yamashita and coworkers, reveals microaneurysm formation because of weakness of the internal elastic lamina and thinness of the vessel wall. The latter lesion is the source of subarachnoid hemorrhage. Thus one part of the symptomatology is traced to the distal carotid stenosis and another to the rupture of the vascular network. Opinion is divided as to whether the basal rete mirabile represents a congenital vascular malformation (i.e., a persistence of the embryonal network) or a rich collateral vascularization secondary to a congenital hypoplasia, acquired stenosis, or occlusion of the internal carotid arteries early in life.
Treatment The treatment of moyamoya is far from satisfactory. Certain surgical measures have been employed, including transplantation of a vascular muscle flap, omentum, or pedicle containing the superficial temporal artery to the pial surface of the frontal lobe temporal pial synangiosis with the idea of creating neovascularization of the cortical convexity. These measures have reportedly reduced the number of ischemic attacks, but whether they alter the natural history of the illness cannot be stated. Anticoagulation is considered risky in view of the possibility of cerebral hemorrhage, but there have not been systematic studies. The reader is referred to a review of the clinical features and surgical treatments by Scott and Smith.