What are the typical radiological findings in a patient suspected of having Moya Moya disease on Magnetic Resonance Imaging (MRI), Magnetic Resonance Angiography (MRA), or Computed Tomography Angiography (CTA)?

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Radiological Findings of Moyamoya Disease

Digital subtraction angiography remains the gold standard for diagnosing moyamoya, but MRI/MRA can establish the diagnosis when all typical findings are present, allowing you to avoid invasive angiography in straightforward cases. 1

Gold Standard: Digital Subtraction Angiography (DSA)

Required diagnostic findings on DSA include: 1

  • Stenosis or occlusion centered on the terminal portion of the intracranial internal carotid artery 1
  • Moyamoya vessels (abnormal vascular networks) in the vicinity of the occlusive lesions visible in the arterial phase - these appear as a characteristic "puff of smoke" pattern at the base of the brain 1, 2
  • Both unilateral and bilateral involvement satisfy diagnostic criteria 1

DSA provides critical information for surgical planning by revealing blood supply from collateral vessels, including those from the external carotid arteries, and confirms the Suzuki stage of disease progression 1. The Suzuki classification characterizes disease stage based on angiographic intensification and decrease of moyamoya collaterals over time, though its practical application in individual cases without serial evaluations is limited 1.

MRI/MRA Findings

MRI with MRA can establish the diagnosis without DSA when all typical findings are present: 1

Required MRI/MRA diagnostic criteria: 1

  • Stenosis/occlusion of the terminal portion of intracranial internal carotid artery
  • Decreased outer diameter of the terminal portion of internal carotid artery and horizontal portion of middle cerebral artery bilaterally on heavy T2-weighted MRI

Virtually diagnostic MRI findings: 1

  • Diminished flow voids in the ICA, MCA, and ACA 1
  • Prominent collateral flow voids in the basal ganglia and thalamus - this combination is virtually diagnostic of moyamoya 1, 3

Additional MRI sequences reveal: 1

Acute/subacute ischemia:

  • Acute infarcts are best seen on diffusion-weighted imaging (DWI) 1, 4
  • Chronic infarcts are better delineated with T1- and T2-weighted imaging 1

Cortical ischemia indicators:

  • FLAIR sequences showing linear high signal following a sulcal pattern - represents slow flow in poorly perfused cortical circulation 1
  • "Ivy sign" - leptomeningeal collateral recruitment visible on FLAIR 1

Common parenchymal lesions (seen in 80% of hemispheres): 5

  • Infarcts in cortical watershed zones, basal ganglia, deep white matter, or periventricular regions 1
  • The extent of anterior circulation occlusion correlates with white matter infarcts 5
  • The extent of posterior circulation occlusion correlates with cortical and/or subcortical infarcts 5

Important MRA limitations: 1

While MRA can detect stenosis of major intracranial vessels, visualization of basal moyamoya collateral vessels and smaller-vessel occlusions is frequently subject to artifact 1. MRA showed moyamoya vessels in only 20 of 24 hemispheres (83%) where conventional angiography showed them in all cases 6. Additionally, MRA tends to overestimate the extent of occlusive disease in approximately 12-15% of vessels 6.

CT and CTA Findings

CT scan alone is inadequate to confirm moyamoya diagnosis, though it can identify complications: 1

CT findings: 1

  • Small areas of hypodensity in cortical watershed zones, basal ganglia, deep white matter, or periventricular regions
  • Hemorrhage (rare in children, more common in adults) in basal ganglia, ventricular system, medial temporal lobes, and thalamus 1, 3

CTA capabilities: 1

  • Can identify arterial narrowing
  • In advanced cases, can demonstrate collateral vessels at the base of the brain
  • Provides a noninvasive alternative when catheter angiography is not feasible 1

Hemodynamic Imaging (Adjunctive)

Cerebral perfusion studies are useful for diagnosis, treatment decisions, and follow-up: 1

Available modalities include: 1

  • MRI with arterial spin labeling
  • Brain CT perfusion
  • Acetazolamide (ACZ)-99mTc-HMPAO-SPECT
  • PET with ACZ challenge
  • Xe-enhanced CT

These techniques detect regional perfusion instability and cerebrovascular reserve capacity, which are important predictors of stroke risk in moyamoya patients 1, 4. They can also determine the extent of perfusion improvement after surgical revascularization 1.

Clinical Pitfalls to Avoid

Do not rely on MRA alone when moyamoya vessels are not clearly visualized - proceed to DSA for definitive diagnosis, as MRA misses moyamoya vessels in approximately 17% of cases 6.

Do not mistake normal flow voids for pathology - the key is finding diminished flow voids in major vessels combined with prominent collateral flow voids in basal ganglia/thalamus 1.

Do not overlook unilateral disease - both unilateral and bilateral involvement satisfy diagnostic criteria, and approximately 20% of patients progress from unilateral to bilateral disease 1.

In pediatric patients, always obtain a full 6-vessel angiogram (bilateral ICAs, VAs, and ECAs) when performing DSA, as this reveals the complete collateral network and assists surgical planning 1.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Research

The Genetic Basis of Moyamoya Disease.

Translational stroke research, 2022

3
Guideline

Anatomical Relationship Between the Thalamus and Circle of Willis

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

4
Guideline

Diagnostic Approach for Patients with Moyamoya Disease and Cancer

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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