MOYAMOYA DISEASE

Two year old male boy presented with recurrent episodes of transient ischemic attacks since the age of 6 months following which he has delayed milestones. The boy also has seizures since one year. He was referred to MRI brain for further evaluation.

Figure a) T1weighted image at the level of basal ganglia show multiple tiny low intensity rounded areas seen in bilateral basal ganglia (arrows) which appear hyperintense on T2 weighted images suggestive of collateral vessels. c) Fluid attenuation inversion recovery (FLAIR) sequence showing atrophy involving bilateral frontal and left parietal cortical areas with chronic ischemic changes. d) Volume rendered 3D time of flight frontal projection cerebral angiography showing significant stenosis in the supraclinoid internal carotid arteries on both the sides with absent flow in the anterior and middle cerebral arteries and multiple collaterals in bilateral basal ganglia appearing as “puff of smoke” (moyamoya). Cause is unknown in this boy.

Discussion:

The term ‘moyamoya’ means ‘wavering puff of smoke’, described by Takaku, Suzuki and others in Japan in the sixties1. Moyamoya disease is a cerebrovascular disease that features narrowing or stenosis, starting at the distal internal carotid and proximal portions of the anterior and middle cerebral arteries of unknown etiology. Moyamoya syndrome is a phenomenon caused by an oligemic state similar in presentation but caused by various disease entities. Some of the conditions associated with Moyamoya syndrome are chromosomal disorders (Neurofibromatosis, Down’s syndrome), hemolytic anemias, infectious diseases (leptospirosis, tuberculous meningitis), neoplasms (Craniopharyngioma, Wilms tumor), drug abuse (phenobarbitol) and others. Etiology of Moyamoya disease is still unknown. There have been recent reports of increased familial incidence of the disease with markers on chromosome 6 and 17, located at 3p24.2-26 and a possible linkage of the marker D6S441 to the disease on chromosome 6. Moyamoya is commonly seen during first decade of life. Frequently the children present with transient ischemic attacks or ischemic strokes. Cerebral ischemia may also present as reversible ischemic neurological deficit, sensory attacks or acute infantile hemiplegia. Headaches, involuntary choreiform movements, seizures and other motor disturbances have been described2.

Majority of children (50-60%) show atrophy of anterior brain more than posterior brain on CT scan, where as adults show hemorrhage especially in intraventricular region. Contrast enhanced CT shows enhancing dots in basal ganglia and ‘net like’ vessels at the base of brain. MRI and MR angiography are diagnostic imaging modality of choice. MRI show multiple dot-like flow voids in basal ganglia on T1 weighted image (WI). Flow voids in the multiple collateral vessels in the cisterns appearing as ‘net like’ cisternal filling defects, associated with hyperintense small vessel cortical and white matter infarcts are seen on T2 WI. Slow flowing engorged pial vessels with thickened arachnoid membranes appear as bright sulci called leptomeningeal “ivy sign”. MR angiography show narrowed distal ICA and proximal Circle of Willis vessels with multiple lenticulostriate and thalamoperforator collaterals giving appearance of a “puff of smoke”. MR spectroscopy will show lactate peak in acutely infracted tissue. Treatment is mainly Encephalo-duro-arterio-synangiosis (EDAS) which is a method of indirect bypass2.

Teaching point:

Moyamoya disease or syndrome should be suspected in a child with recurrent ischemic attacks. MRI with MR angiography is the investigation of choice in this condition. MRI shows multiple dot-like flow voids in basal ganglia on T1 WI and flow voids in the multiple collateral vessels in the cisterns appear as ‘net like’ cisternal filing defects on T2WI. MR angiography show narrowed distal ICA and proximal Circle of Willis vessels with multiple lenticulostriate and thalamoperforator collaterals giving appearance of a “puff of smoke” which is typical appearance of moyamoya.

References:

1. Hoffman HJ. Moyamoya disease and syndrome. Clin Neurol Neurosurg1997; 99 Suppl 2 : S39-44
2. Gosalakkal JA. Moyamoya disease: a review. Neurol India. 2002 Mar;50(1):6-10.
3. Fujisawa I, Asato R, Nishimura K, Togashi K, Itoh K, Noma S, et al. Moyamoya disease: MR imaging. Radiology. 1987 Jul;164(1):103-5.