• pediatric stroke is increasingly being recognized as an important cause of morbidity and mortality
    • over 75% of children suffer long-term neurological deficits 
    • mortality ~ 10% 
    • 19% recurrence within 5 years
  • it has a unique presentation (that may delay correct diagnosis) and etiologies (→ etiology of pediatric stroke)
    • the diagnosis of stroke is often challenging in infants and children because nonspecific localizing signs are frequently overlooked
    • according to one study, only 20% of children were diagnosed with stroke within six hours, and stroke was not suspected in over 62% of children at initial presentation (Rafay, 2009)
  • neuroimaging is an essential component of pediatric stroke management as it helps to:
    • confirm the diagnosis and type of stroke (ischemic x hemorrhagic)
    • exclude stroke mimics (PRES, epilepsy, CNS infection, tumor, etc.)
    • identify the stroke etiology (dissection, vasculitis, moyamoya, etc.)
    • facilitate treatment decisions (acute therapy, prevention)
    • provide prognostic information

Overview of neuroimaging modalities

  • the choice of modality depends on the patient’s age, the clinical scenario, and hospital resources
  • non-contrast head CT (NCCT) is typically the initial imaging method in a child with stroke symptoms (due to factors such as availability, speed, sensitivity for ICH, etc.)

CT + CT angiography

  • NCCT has limited sensitivity for the detection of acute pediatric stroke and frequent stroke mimics + requires exposure to ionizing radiation and iodinated contrast dye
  • if possible, magnetic resonance imaging (MRI) is preferred
  • if MRI is contraindicated or unavailable, perform NCCT+CT angiography of the head and neck, with or without CT venography

MRI + MR angiography

  • MRI + MRA/MRV + MR perfusion are optimal for obtaining the definitive diagnosis of both ischemic and hemorrhagic lesions, as well as for identifying underlying arteriopathy, thrombus, or arterial dissection in both neonates and older children
  • many centers have implemented rapid brain MRI protocols for stroke to shorten examination time; the rapid protocol typically includes:
    • diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps   → DWI in acute stroke diagnosis
    • gradient echo (GRE) sequences or susceptibility-weighted imaging (SWI) to detect hemorrhage
    • MR angiography
    • MR perfusion
      • arterial spin labeling (ASL) –  not extensively validated in pediatric stroke
      • contrast-enhanced perfusion imaging (PWI) is less often used
        • dynamic bolus passage of gadolinium with rapid T2* weighting (dynamic susceptibility contrast, DSC)
        • dynamic bolus passage of gadolinium with T1 weighting (dynamic contrast enhancement, DCE)
    • vessel wall imaging (VWI) – to detect inflammatory processes or dissection

Digital subtractive angiography

  • can be considered when the cause of the infarction is unclear from non-invasive imaging studies and when there is a high clinical suspicion of a medium to small-sized arteriopathy
  • it has better sensitivity for aneurysms, vasculopathies involving medium-small vessels, or other structural vascular disorders

Perfusion methods (CTP, MRP, SPECT)

  • important methods to assess hemodynamic changes when revascularization procedures are considered (bypass or synangiosis considered in vasculopathies such as moyamoya)
  • strict perfusion parameters are not established in children; physiologic and hemodynamic differences should be expected

Neuroimaging in different stroke subtypes

→ Etiology of pediatric stroke

→ Recanalization therapy in pediatric stroke

  • some disorders are more frequent in pediatric stroke compared to adults:
    • focal cerebral arteriopathy (FCA), also known as transient cerebral arteriopathy (TCA)
    • primary and secondary Moyamoya disease
    • genetic or syndromic arteriopathies (such as PHACE syndrome, ACTA2 angiopathy, Grange syndrome, etc.)
    • vasculitis
    • fibromuscular dysplasia
    • iatrogenic stroke
    • dissection
    • hypercoagulable states (thrombophilia)

Computed tomography (CT)

  • CT is often the first imaging modality performed when MRI is not available, or the child is unstable
    • excludes intracranial hemorrhage but is insensitive to hyperacute or small ischemic infarctions
    • infarction has a similar appearance to that in the older child or adult, manifesting as a well-defined, often wedge-shaped region of hypoattenuation in an arterial distribution
  • CTA is used to detect artery stenosis or occlusion

Magnetic resonance imaging (MRI)

  • modality of choice in pediatric stroke; the appearance of infarction is the same as in adults
  • DWI
    • MRI shows reduced diffusivity within minutes, presenting as a high signal on DWI and low computed values on ADC maps
    • high signal on DWI increases continually in the hyperacute and acute phases, peaking commonly after several days
    • a transient pseudo-normalization may be observed for days, with diffusivity then increasing to supranormal levels (the development and evolution of pseudonormalization on ADC will commonly precede that on DWI)
    • a pediatric modification of the ASPECTS (pedASPECTS) score was developed using DWI (Mackay, 2020)

      • the score includes two regions of the anterior (A1 and A2), 10 areas of the middle (M1, M2, M3, M4, M5, M6, insula, internal capsule, caudate, and lentiform nucleus), and three regions of the posterior cerebral artery territories (P1, P2, and thalamus) in each hemisphere. One point is allocated to each area affected by infarction; the total pedASPECTS ranges from 0 for normal to 30 for maximal severity (15 per hemisphere)
  • DWI-FLAIR mismatch
    • a positive DWI with negative findings on FLAIR suggests a stroke onset of < 4.5 hours ago
  • MRA and vessel wall imaging

    • MRA helps identify the site and extent of stenosis or occlusion
    • if arteriopathy is suspected, vessel wall imaging (using black-blood, T1-weighted post-contrast imaging) can demonstrate abnormal vessel wall enhancement in the setting of active inflammatory processes, as well as assess for intracranial arterial dissection on pre-contrast T1-weighted imaging
    • some genetic arteriopathies have unique imaging appearances, such as ACTA2 mutation, which demonstrates dilation of the proximal internal carotid arteries, occlusion or narrowing of the distal internal carotid arteries, straight “broomstick-like” arteries of the circle of Willis, and absence of lenticulostriate collaterals
  • MR perfusion
    • DWI-perfusion weighted imaging (PWI) mismatch may be used to assess penumbra (validation in children is lacking)
    • arterial spin labeling (ASL) is not an established method in acute stroke
      • ASL can identify areas of reduced or increased perfusion, helping to differentiate lesions causing stroke or stroke symptoms from mimics; age-specific labeling protocols should be employed
    • perfusion imaging helps identify regions of relative ischemia that are at risk for infarction in Moyamoya syndrome
  • pediatric hemorrhagic stroke (intracerebral hemorrhage, ICH) has different causes compared to adults (where hypertensive bleeding prevails)
    • rupture of vascular malformations or aneurysms
    • hemorrhagic venous infarction (CSVT)
    • coagulopathy
    • infant intraventricular hemorrhage (IVH)
    • genetic arteriopathies associated with hemorrhagic stroke (IVA or JAM3 mutations)
  • imaging should:
    • differentiate hemorrhagic transformation (arterial or venous) from primary hemorrhage
    • detect an underlying mass or vascular malformation as a source of bleeding
  • CT – usually the baseline imaging
    • excellent sensitivity for the detection of hemorrhage
    • CTA can detect underlying vascular pathology
  • MRI – preferred in stable patients (T1,2, FLAIR, DWI, SWI/GRE, MRA, and/or MRV)
  • DSA – may be considered if no lesion is identified on initial imaging to assess for small vascular malformation
  • if no malformation is identified on baseline imaging, repeat the neuroimaging after the hematoma has resolved (as small lesions can be compressed)
  • venous infarcts caused by cerebral sinus venous thrombosis (CSVT) are relatively common (accounting for ~ 40% of CSVT cases)
  • approximately 70% of these infarcts are hemorrhagic
  • thrombosis should be suspected in any child who has an unexplained hemorrhage or an infarction that does not fit an arterial vascular distribution
  • risk factors include:
    • head and neck infections
    • chronic diseases such as connective tissue disorders
    • coagulation disorders
  • MRI is the imaging modality of choice
    • T1- and T2-weighted images + DWI, GRE/SWI images, and MRV
    • acute (<3 days) thrombus exhibits low signal intensity due to the presence of deoxygenated hemoglobin
    • in subacute thrombosis (>4-5 days), T1-weighted images show the high signal intensity of the clot
    • GRE helps detect cortical vein thrombosis
  • CT venography
    • sensitive and specific for diagnosing dural sinus thrombosis
    • disadvantages:
      • radiation and contrast dye exposure
      • limited diagnostic value for diagnosing cortical vein thrombosis

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Neuroimaging in pediatric stroke
link: https://www.stroke-manual.com/neuroimaging-in-pediatric-stroke/