A 12 year old male child was brought with complains of seizures (3-4 episodes). The patient had a past history of similar complaints 4 months back. No associated history of fever, trauma to the head, previous surgery or any other major illness. Birth history and family history were non-contributory.
MRI revealed attenuated flow void of the cavernous and supra-clinoid portion of the right internal carotid artery (ICA) with non-visualization of proximal portions of the right anterior cerebral artery (ACA) and middle cerebral artery (MCA). There were multiple flow voids representing small vascular channels in the suprasellar region extending into right Sylvian fissure.
MR angiography demonstrated uniform narrowing of the right ICA (from its origin till intracranial portion) compared to the left ICA with non-visualization of the A1 segment of right ACA and M1 segment of the right MCA. Overall paucity of vessels was seen in the right cerebral hemisphere, especially in the right MCA territory. Multiple small vascular channels were seen in the right Sylvian fissure and suprasellar cistern. The rest of the vessels of the circle of Willis appeared normal. Left ICA was normal in course and caliber. The vertebro-basillar system was normal.
Moyamoya means 'hazy' in Japanese. It is a rare vasculopathy that affects the main intracranial vessels. The reported incidence of moyamoya in the Asian population is approximately 3 cases per 100,000 in a paediatric population . The title of moyamoya disease is reserved for an idiopathic and many times familial condition, however numerous systemic disorders such as neurofibromatosis type I, tuberous sclerosis, connective tissue disorders, Grave’s disease, fibromuscular dysplasia, meningitis, sickle cell anemia and Down’s syndrome can cause it.
The disease is characterized by progressive stenosis at the apices of the intracranial internal carotid arteries (ICA), including the proximal anterior cerebral arteries and middle cerebral arteries. Tiny collateral vessels develop on the cortical surface, leptomeninges, dura and skull base leading to an extensive network of enlarged basal, transcortical and transdural vessels. Clinically, a patient can present with either ischaemic, haemorrhagic or epileptic complaints. The childhood disease often presents with cerebral infarction in comparison to adult-onset, which often presents with intracranial haemorrhage, arising from rupture of delicate collateral vessels.
CT in a patient with moyamoya disease may show small areas of hypodensity suggestive of ischemic changes in the cortical watershed zones, basal ganglia, deep white matter, or periventricular regions. CT angiography (CTA) can effectively demonstrate intracranial stenosis. The finding most diagnostic of moyamoya on MRI is reduced flow voids in the internal, middle, and anterior cerebral arteries coupled with prominent flow voids through the basal ganglia and thalami representing collaterals. FLAIR sequences show “ivy sign” i.e. linear high signal along the fissures and gyri of cerebral hemispheres, resulting most probably from the reduction of the cortical flow . Thus, the definitive diagnosis as with many other diseases is based on conventional angiographic findings. Angiography should consist of a full 6-vessel series (both internal carotid arteries, external carotid arteries and vertebral arteries). Perfusion studies have revealed a number of intriguing findings including reduction in bifrontal perfusion with increase or normal occipital blood flow, decrease in cerebrovascular reserve (CVR) and cerebral blood flow (CBF) with increase in cerebral blood volume (CBV) and oxygen extraction fraction (OEF).
Medical therapy includes antiplatelet medicines. Anticoagulative therapy is not recommended due to risk of bleeding. Surgery includes direct anastomoses between the superficial temporal artery and the middle cerebral artery (STA-MCA anastomosis) as well as indirect procedures involving synangiosis i.e. placement of vascularised tissue in the brain cortex to promote neoangiogenesis.
Differential Diagnosis List