II. Definitions
- Moyamoya
- Noninflammatory progressive Occlusion of the intracranial carotid arteries, triggering CVA findings, typically in children
- Results from arterial wall thickening, endothelial hyperplasia and fibrosis either with associated conditions (MMS) or genetic/idiopathic (MMD)
- Carotid Stenosis with secondary formation of collateral arteries from the Circle of Willis in a netlike configuration
- Netlike appearance on angiogram is described as a "Puff of Smoke", or in Japanase Moyamoya
- Moyamoya Disease (MMD)
- Idiopathic (and with possible defined gene defect), Moyamoya Disease (MMD) is without the associated conditions typical for MMS
- Moyamoya Syndrome (MMS)
- Associated with other conditions (e.g. Trisomy 21, Neurofibromatosis, Sickle Cell Anemia)
III. Epidemiology
- Primarily onset in children, presenting with Ischemic CVA or TIA in 80% of cases
- Less commonly may have onset in adulthood, often with hemorrhagic presentations
IV. Mechanism
- Noninflammatory progressive Occlusion of the intracranial carotid arteries, triggering CVA findings, typically in children
- Results from arterial wall thickening, endothelial hyperplasia and fibrosis either with associated conditions (MMS) or genetic/idiopathic (MMD)
- Internal Carotid Artery Stenosis progresses to affect the anterior cerebral arteries and middle cerebral arteries
- Secondary formation of collateral arteries from the Circle of Willis in a netlike configuration (appears as "Puff of Smoke", or in Japanase Moyamoya)
- Collateral vessels expand at the lenticulostriate, leptomeningial, thalamoperforating and dural arteries over the course of years into adulthood
- Collateral vessels are fragile and more prone to rupture
V. Associated Conditions: Moyamoya Syndrome (MMS)
- Trisomy 21
- Neurofibromatosis
- Sickle Cell Anemia
- Thyroid Disease
- Prior Radiation Therapy
VI. Imaging
-
CT Head and CTA Head and Neck
- Often the initial imaging study in acute Cerebrovascular Accident in the first 24 hours
-
MRI Brain and MRA Head and Neck
- Preferred in Moyamoya, especially in children if no delay
- Digital Subtraction Angiography
- Gold standard, and used during intervention
- Significant radiation exposure and largerly replaced by CTA and MRA for diagnostic purposes
VII. Presentations
-
Cerebrovascular Accident (CVA)
- Transient Ischemic Attacks and CVAs represent 80% of Moyamoya presentations in children
- Events often provoked by hypocapnea induced vasonconstriction (e.g. straining, Hyperventilation)
-
Cerebral Aneurysm formation and Hemorrhagic CVA or Intracranial Hemorrhage
- Typical presentation in adults with Moyamoya, due to rupture of fragile collateral vessels
- Rupture is most common in the Basal Ganglia and Hypothalamus, but other aneurysmal rupture sites occur
VIII. Staging
- Stage 1: Carotid fork narrowed
- Stage 2: Moyamoya initiation
- Large and obscure carotid fork
- Enlarged main arterial vessels without collaterals
- Stage 3: Moyamoya intensify
- Main intracerebellar artery changes, with some arterial replacement with Moyamoya
- Stage 4: Moyamoya minimization
- Internal Carotid ArteryOcclusion up to the Posterior Communicating Artery junction
- Rough, poor Moyamoya network
- Stage 5: Moyamoya reduced
- Disappearance of Internal Carotid Artery branches, and minimization of other vessels
- Increased collateral flow
- Stage 6: Moyamoya disappear
- Disappearance of main Moyamoya-involved vessels at brain base
- Vertebral arteries and external carotid arteries maintain flow, but other major vessels have all been replaced by collaterals
IX. Management
- No medical management reverses or prevents Moyamoya progression
- However, revascularization improves cerebral perfusion and reduces complication risk
- Refer all Moyamoya patients to neurosurgery
- Direct and indirect bypass methods are used depending on patient's age and staging
-
Ischemic CVA or TIA is typically treated with Antiplatelet Therapy (Aspirin, Clopidogrel)
- However, increases risk of Hemorrhagic CVA complications
-
Intracranial Hemorrhage
- Neurosurgical management
- Obstructive Hydrocephalus may require ventricular drain
X. References
- Blalock (2022) Crit Dec Emerg Med 36(10): 20-2
- Lee (2017) J Child Neurol 32(11): 924-9 [PubMed]
- Suzuki (1969) Arch Neurol 20(3): 288-99 [PubMed]
- Yamamoto (2020) Neurol Med Chir 60(7): 360-7 [PubMed]