Moyamoya Disease

Aka: Moyamoya Disease, Moya Moya Disease, Moyamoya Syndrome, Moyamoya

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II. Definitions

  1. Moyamoya
    1. Noninflammatory progressive Occlusion of the intracranial carotid arteries, triggering CVA findings, typically in children
    2. Results from arterial wall thickening, endothelial hyperplasia and fibrosis either with associated conditions (MMS) or genetic/idiopathic (MMD)
    3. Carotid Stenosis with secondary formation of collateral arteries from the Circle of Willis in a netlike configuration
    4. Netlike appearance on angiogram is described as a "Puff of Smoke", or in Japanase Moyamoya
  2. Moyamoya Disease (MMD)
    1. Idiopathic (and with possible defined gene defect), Moyamoya Disease (MMD) is without the associated conditions typical for MMS
  3. Moyamoya Syndrome (MMS)
    1. Associated with other conditions (e.g. Trisomy 21, Neurofibromatosis, Sickle Cell Anemia)

III. Epidemiology

  1. Primarily onset in children, presenting with Ischemic CVA or TIA in 80% of cases
    1. Less commonly may have onset in adulthood, often with hemorrhagic presentations

IV. Mechanism

  1. Noninflammatory progressive Occlusion of the intracranial carotid arteries, triggering CVA findings, typically in children
    1. Results from arterial wall thickening, endothelial hyperplasia and fibrosis either with associated conditions (MMS) or genetic/idiopathic (MMD)
    2. Internal Carotid Artery Stenosis progresses to affect the anterior cerebral arteries and middle cerebral arteries
  2. Secondary formation of collateral arteries from the Circle of Willis in a netlike configuration (appears as "Puff of Smoke", or in Japanase Moyamoya)
    1. Collateral vessels expand at the lenticulostriate, leptomeningial, thalamoperforating and dural arteries over the course of years into adulthood
    2. Collateral vessels are fragile and more prone to rupture

V. Associated Conditions: Moyamoya Syndrome (MMS)

  1. Trisomy 21
  2. Neurofibromatosis
  3. Sickle Cell Anemia
  4. Thyroid Disease
  5. Prior Radiation Therapy

VI. Imaging

  1. CT Head and CTA Head and Neck
    1. Often the initial imaging study in acute Cerebrovascular Accident in the first 24 hours
  2. MRI Brain and MRA Head and Neck
    1. Preferred in Moyamoya, especially in children if no delay
  3. Digital Subtraction Angiography
    1. Gold standard, and used during intervention
    2. Significant Radiation Exposure and largerly replaced by CTA and MRA for diagnostic purposes

VII. Presentations

  1. Cerebrovascular Accident (CVA)
    1. Transient Ischemic Attacks and CVAs represent 80% of Moyamoya presentations in children
    2. Events often provoked by hypocapnea induced vasonconstriction (e.g. straining, Hyperventilation)
  2. Cerebral Aneurysm formation and Hemorrhagic CVA or Intracranial Hemorrhage
    1. Typical presentation in adults with Moyamoya, due to rupture of fragile collateral vessels
    2. Rupture is most common in the Basal Ganglia and Hypothalamus, but other aneurysmal rupture sites occur

VIII. Staging

  1. Stage 1: Carotid fork narrowed
  2. Stage 2: Moyamoya initiation
    1. Large and obscure carotid fork
    2. Enlarged main arterial vessels without collaterals
  3. Stage 3: Moyamoya intensify
    1. Main intracerebellar artery changes, with some arterial replacement with Moyamoya
  4. Stage 4: Moyamoya minimization
    1. Internal Carotid ArteryOcclusion up to the Posterior Communicating Artery junction
    2. Rough, poor Moyamoya network
  5. Stage 5: Moyamoya reduced
    1. Disappearance of Internal Carotid Artery branches, and minimization of other vessels
    2. Increased collateral flow
  6. Stage 6: Moyamoya disappear
    1. Disappearance of main Moyamoya-involved vessels at brain base
    2. Vertebral arteries and external carotid arteries maintain flow, but other major vessels have all been replaced by collaterals

IX. Management

  1. No medical management reverses or prevents Moyamoya progression
    1. However, revascularization improves cerebral perfusion and reduces complication risk
    2. Refer all Moyamoya patients to neurosurgery
    3. Direct and indirect bypass methods are used depending on patient's age and staging
  2. Ischemic CVA or TIA is typically treated with Antiplatelet Therapy (Aspirin, Clopidogrel)
    1. However, increases risk of Hemorrhagic CVA complications
  3. Intracranial Hemorrhage
    1. Neurosurgical management
    2. Obstructive Hydrocephalus may require ventricular drain

X. References

  1. Blalock (2022) Crit Dec Emerg Med 36(10): 20-2
  2. Lee (2017) J Child Neurol 32(11): 924-9 [PubMed]
  3. Suzuki (1969) Arch Neurol 20(3): 288-99 [PubMed]
  4. Yamamoto (2020) Neurol Med Chir 60(7): 360-7 [PubMed]

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