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MRI Brain: Sickle Cell Vasculopathy

MRI of the brain characterises the cerebrovascular consequences of sickle cell disease, including overt and silent infarcts, haemorrhage and large-vessel vasculopathy such as moyamoya. Unlike TCD, which estimates stroke risk, MRI with MRA depicts established parenchymal injury and vessel anatomy to guide transfusion and surgical revascularisation decisions. It is the study of choice for neurological symptoms, stroke evaluation and surveillance of silent cerebral infarction.

Indications

  • Acute neurological deficit or suspected stroke in sickle cell disease
  • Seizures, cognitive decline or headache warranting infarct assessment
  • Surveillance for silent cerebral infarction guiding therapy
  • Abnormal or low TCD velocities requiring vessel characterisation
  • Suspected moyamoya vasculopathy or progressive large-vessel stenosis
  • Pre-operative or pre-transplant neurological assessment and monitoring of therapy response

Contraindications & Cautions

  • Standard MRI contraindications: incompatible pacemakers, certain implants, ferromagnetic foreign bodies
  • Gadolinium: avoid or use macrocyclic agents cautiously in significant renal impairment (nephrogenic systemic fibrosis risk); most vasculopathy assessment uses non-contrast MRA and is achievable without gadolinium
  • Sedation risk in young children with cardiorespiratory compromise - involve anaesthesia and optimise hydration/oxygenation to avoid provoking sickling
  • Claustrophobia may require sedation or open-bore systems

Patient Preparation

  • Ensure adequate hydration, oxygenation and warmth to reduce the risk of sickling during the study
  • Screen thoroughly for MRI-incompatible implants and complete a safety checklist
  • Young or uncooperative children may need sedation or general anaesthesia with appropriate monitoring
  • Explain the procedure and obtain informed consent/assent
  • Review haemoglobin, recent transfusion and TCD history to contextualise findings
  • 3T is preferred where available for higher-resolution vessel imaging

Technique & Parameters

  • Core sequences: axial T1, T2, FLAIR, DWI with ADC, and susceptibility-weighted imaging or GRE for haemorrhage/microbleeds
  • 3D time-of-flight MRA of the circle of Willis for stenosis, occlusion and moyamoya
  • FLAIR for chronic infarcts and periventricular white matter disease; DWI for acute ischaemia
  • Consider perfusion imaging (ASL avoids gadolinium) to assess haemodynamic reserve
  • Slice thickness around 3-5 mm for structural sequences; thin overlapping slabs for MRA
  • Add MR venography if venous thrombosis is a consideration; contrast reserved for specific vascular/inflammatory questions

Systematic Review

  • Screen frontal and parietal deep white matter and watershed zones for silent infarcts on FLAIR
  • Assess DWI/ADC for acute infarction and its arterial territory
  • Evaluate SWI/GRE for microbleeds, prior haemorrhage or haemosiderin
  • Review MRA for stenosis, occlusion and the distal ICA/proximal MCA-ACA moyamoya pattern
  • Look for basal collateral vessels and the ivy sign of leptomeningeal collateralisation
  • Assess for subarachnoid or parenchymal haemorrhage and aneurysms
  • Correlate parenchymal injury with vascular territory and TCD data

Key Findings & Significance

  • Silent cerebral infarcts: small FLAIR hyperintensities in frontal/parietal white matter and watershed zones without acute deficit
  • Acute infarct: restricted diffusion in a territorial or borderzone distribution
  • Intracranial haemorrhage: parenchymal or subarachnoid, sometimes from associated aneurysms or moyamoya collaterals
  • Moyamoya pattern: progressive supraclinoid ICA and proximal MCA/ACA stenosis with basal collaterals
  • Cerebral microbleeds on SWI reflecting chronic vasculopathy
  • Vessel stenosis/occlusion on MRA identifying territory at risk and guiding transfusion or revascularisation

Differential Considerations

  • White matter FLAIR foci: silent sickle infarcts versus non-specific gliosis, demyelination or migraine-related lesions
  • Territorial infarct: large-vessel sickle vasculopathy, embolism, moyamoya collateral failure
  • Progressive ICA/MCA stenosis: sickle moyamoya versus idiopathic moyamoya or vasculitis
  • Parenchymal haemorrhage: ruptured moyamoya collateral, aneurysm, hypertensive bleed
  • Microbleeds: chronic sickle vasculopathy versus hypertensive or amyloid angiopathy (age-dependent)
  • Watershed injury: chronic anaemic hypoperfusion versus acute hypotensive event

Pearls & Pitfalls

  • Silent infarcts are common, associated with cognitive impairment and predict future overt stroke
  • Non-contrast TOF MRA usually suffices - avoid gadolinium where renal function is impaired
  • Optimise oxygenation and hydration around sedation to prevent iatrogenic sickling
  • Watershed distribution reflects the chronic anaemic, hyperdynamic circulation
  • Correlate MRA vasculopathy with TCD; low TCD velocities can reflect severe stenosis rather than reassurance
  • Look specifically for moyamoya collaterals and the ivy sign, which change management

Structured Report

  • List sequences performed and whether MRA/contrast were used
  • Describe acute and chronic infarcts with location, territory and diffusion characteristics
  • Report haemorrhage, microbleeds and any aneurysm
  • Detail MRA findings: stenosis, occlusion, moyamoya pattern and collaterals
  • Compare with prior imaging to assess progression
  • Impression: integrate parenchymal and vascular findings with TCD and clinical status; advise on transfusion/revascularisation referral and follow-up interval

References

  • DeBaun MR et al., SIT Trial: Silent Cerebral Infarcts and Transfusion (NEJM 2014)
  • American Society of Hematology Guidelines: Cerebrovascular Disease in Sickle Cell Disease
  • ACR Appropriateness Criteria: Cerebrovascular Disease
  • RadioGraphics: Neuroimaging of Sickle Cell Disease

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.