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KEY FACTS

Terminology
- Acute neurologic dysfunction due to loss of vascular integrity
Imaging
- NECT: ↓ attenuation of affected gray matter - Insular ribbon sign → loss of distinct insular cortex - Hyperdense MCA sign → thrombosed MCA
- MR: ↓ diffusion within ~ 30 minutes of arterial occlusion - Cytotoxic edema evident in affected territory on FLAIR/T2 by 4-6 hours after arterial occlusion - Enhancement of infarct typically occurs after 5-7 days
- CTA/MRA: Critical for early evaluation & identification of possible etiology (e.g., dissection, arteriopathy)
- MR perfusion imaging can provide valuable information regarding region at risk in setting of acute stroke - Arterial spin labeling (ASL) can provide useful perfusion information without contrast administration
Top Differential Diagnoses
- Seizure-related injury
- Acute encephalitis
- Mitochondrial encephalopathies
- Posterior reversible encephalopathy syndrome
Pathology
- Major causes: Cardiac disease (~ 25%), moyamoya-type arteriopathy, dissection, vasculitis, hematologic/metabolic
- No underlying cause discovered in ~ 25% of cases
Clinical Issues
- Incidence: 2-3/100,000 per year in USA - Mortality: 0.6/100,000
- Children typically present later than adults (> 24 hours)
- Focal deficit may be masked by lethargy, coma, irritability
- Treatment in pediatric acute stroke usually conservative - Thrombolysis/thrombectomy not well studied in children
- Capacity for recovery in children much > adults
Diagnostic Checklist
- When stroke is suspected clinically or by imaging, do not hesitate to perform vessel imaging

TERMINOLOGY

Synonyms
- Cerebrovascular accident, cerebral infarct, cerebral ischemia
Definitions
- Acute alteration of neurologic function due to loss of vascular integrity - This chapter specifically addresses arterial ischemia beyond perinatal period

IMAGING

General Features

Best diagnostic clue

- Cytotoxic edema & restricted diffusion (acutely) in affected vascular territory

Location

- Proximal & distal middle cerebral artery (MCA) territory most commonly affected

Morphology

- Stroke caused by arterial occlusion typically conforms to 1 arterial territory

CT Findings

NECT

- ↓ attenuation of affected gray matter with loss of normal gray matter-white matter differentiation
        - ↓ in white matter attenuation less pronounced
        - Often wedge-shaped & localized to 1 arterial territory
        - Diffuse ischemic injury can lead to reversal sign with gray matter diffusely ↓ in attenuation relative to white matter
- Insular ribbon sign → loss of distinct of insular cortex
- Hyperdense MCA sign → ↑ density of acutely thrombosed MCA
- Hemorrhagic transformation (HT)
        - Symptomatic HT in 3%; asymptomatic HT in 30%
                  - Asymptomatic HT usually parenchymal
        - White matter or deep nuclear hemorrhage often mass-like → hematoma within infarcted tissue

CECT

- Enhancement of infarcted territory typically occurs after 5-7 days

CTA

- Invaluable for demonstrating focal vascular abnormalities in acute setting
        - Intimal flap in acutely dissected vessel
        - Major arterial occlusion may prompt thrombolysis or mechanical thrombectomy in appropriate setting

MR Findings
- T1WI: Acute: ↓ signal with gyral swelling - Chronic: ± ↑ signal in cortical laminar necrosis
- T1WI FS: Allows identification of mural hematoma (↑ signal) in dissected vessel
- T2WI: Loss of flow void in thrombosed vessel
- FLAIR: ↑ signal with gyral swelling (within 4-6 hours) - Abnormal sulcal ↑ signal (climbing ivy sign) of chronic, slow-flow collaterals in setting of longstanding proximal vascular occlusion
- DWI: Most sensitive for early detection of ischemia - Acute: Restricted diffusion (↑ DWI, ↓ ADC signal) ≤ 30 minutes after ischemic insult - Subacute (7-14 days): Pseudonormalization of signal - ↑ DWI, ADC ~ brain parenchyma - Chronic: Facilitated diffusion in gliotic brain - ↑/~ DWI, ↑ ADC
- SWI/T2 GRE*: May see ↑ size & number of cortical vessels - Suggests ↑ extraction fraction & possibly recoverable brain
- T1WI C+: Cortical & leptomeningeal enhancement seen after 5-7 days following acute infarct - Enhancing climbing ivy sign
- MRA: Can detect arterial occlusion & stenosis in large- & medium-sized cerebral vessels - Important to identify underlying dissection or arteriopathy
- PWI: Provides valuable information about affected brain - Ischemic penumbra: ↓ perfusion, no DWI change (PWI-DWI mismatch) - May define brain salvageable with acute stroke therapy - Arterial spin labeling can provide useful perfusion information without contrast administration
- MRS: ↑ lactate hallmark of ischemia/infarct - Not specific
- Vessel wall imaging: Vessel wall enhancement patterns improve discrimination of underlying stroke etiology

Ultrasonographic Findings

Grayscale ultrasound

- Affected territory hyperechoic in acute/subacute stage

Color Doppler

- Direct Doppler evaluation ideal for surveillance of vascular occlusion in neonate with open sutures
- Transcranial Doppler evaluation of circle of Willis through temporal squamosa
        - ↑ velocities can predict stenoses detectable by MRA
        - Used as screening tool in children with sickle cell anemia

Angiographic Findings
- Catheter angiography rarely necessary in acute evaluation of childhood stroke - Justified if contemplating endovascular therapy
- Best modality for detailed evaluation of primary arteriopathies
Nuclear Medicine Findings
- PET & SPECT techniques can be used to - Identify salvageable regions at risk (ischemic penumbra) - Demonstrate effects of synangiosis surgery in moyamoya-type vasculopathies

Imaging Recommendations

Best imaging tool

- CT initial imaging test for signs/symptoms of stroke; excellent for excluding hemorrhagic stroke (more common in children vs. adults)
- MR with DWI, MRA, PWI

Protocol advice

- Contrast can help in assessing timing of injury & performing perfusion imaging
- Consider dedicated vessel wall imaging

DIFFERENTIAL DIAGNOSIS

Seizure-Related Injury
- Swelling & restricted diffusion secondary to persistent seizure activity
- Differentiation by clinical presentation & EEG
Acute Encephalitis
- Acute parenchymal inflammation secondary to infectious agents, typically viral
- Slower onset with encephalopathy
Mitochondrial Encephalopathies
- Symmetric basal ganglia involvement common
- Usually have manifestations beyond CNS
Posterior Reversible Encephalopathy Syndrome
- Patchy cortical/subcortical edema most common in parietal & occipital lobes, typically in setting of hypertension
- Diffusion restriction uncommon
Neonatal Herpes Encephalitis
- Infant with seizures 2-5 weeks after birth
- DWI most sensitive for detection in early disease
- Often bilateral with temporal predominance, but can occur anywhere
MELAS
- Mitochondrial encephomyopathy, lactic acidosis, stroke-like episodes
- Areas of ischemia crossing arterial territories, often parietal
- MRS: ↑ lactate in normal-appearing brain
Group B Strep Meningitis
- Associated vasculitis causes ischemia in small perforating arteries
- Unilateral or bilateral deep gray nuclei ischemia

PATHOLOGY

General Features
- 6 major causes of arterial stroke in children - Cardiac disease (~ 25%) - Congenital heart disease, valvular heart disease, arrhythmias, & cardiomyopathies - Moyamoya-type arteriopathy - Sickle cell disease - Neurofibromatosis type 1 - Radiation therapy - Trisomy 21 - Alagille syndrome - Arterial dissection (e.g., trauma) - CNS vasculitis - Hematologic/metabolic (e.g., coagulopathy) - Idiopathic (~ 25%) - No underlying cause discovered

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Depend on patient age, etiology, & involved artery
        - < 1 year: Seizures, encephalopathy > focal neurologic
        - > 1 year: Usually focal neurologic (e.g., hemiplegia, early hand preference)
        - Speech difficulties, gait abnormality, seizure
                  - Seizure → deficit often attributed to postictal state (Jacksonian paralysis)
        - Embolic cause: Sudden onset of symptoms
        - Stenoocclusive cause: Gradual/intermittent (e.g., TIA)
- Focal deficit may be masked by lethargy, coma, irritability

Children typically present later than adults (> 24 hours) - Poor recognition/understanding of symptoms by child, caregiver, physician - Uncommon diagnosis in children requires high degree of suspicion

Demographics

Age

- Incidence/mortality greatest < 1 year
- Large percentage occur in perinatal period
        - Perinatal arterial ischemic stroke (PAIS)

Epidemiology

- Incidence: 2-3/100,000 per year in USA
        - Mortality: 0.6/100,000
- Underrecognized as significant source of morbidity in pediatric population

Natural History & Prognosis
- Capacity for recovery better than in adults, due to - Better compensatory mechanisms, collateral recruitment, neuronal plasticity - Fewer concomitant risk factors
Treatment
- Clinical window of opportunity/benefit not as well understood in children as compared to adults
- Mainstay of chronic therapy for fixed vascular lesions & vasculopathies: Aspirin
- Transfusion therapy for at-risk children with sickle cell
- Mechanical thrombectomy may be considered in certain patient presentations

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls
- Use same imaging signs as adults
- Have low threshold for use of CTA

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References

Selected References

Images

Selected Images

Axial NECT in a 15-year-old girl with dilated cardiomyopathy shows a large area of low attenuation in the right middle cerebral artery (MCA) territory . Note the sulcal effacement & loss of the gray matter-white matter differentiation.

Axial DWI MR in the same patient confirms restricted diffusion in the right MCA territory . Also note the focus of restricted diffusion in the left periventricular region . Multiple infarcts in multiple vascular territories should raise suspicion of a proximal embolic source.

Axial DWI MR in a 6 year old with imbalance and acute infarct of the left basal ganglia shows diffusion restriction (↓ADC not shown). Acute infarct in a child should prompt further evaluation with MRA or CTA to detect an underlying vessel abnormality.

3D MRA of the circle of Willis in the same patient shows irregular narrowing of the left proximal and distal segments of the middle cerebral artery, consistent with vasculitis.

Axial TOF MRA in a 2 year old with multiple infarcts of various ages shows multiple small areas of flow-related signal in the bilateral thalami, consistent with lenticulostriate collaterals of moyamoya.

Axial DWI MR in the same 2-year-old girl with moyamoya-type vasculopathy shows diffusion restriction in the right frontoparietal foci of signal abnormality , suggesting an acute/subacute infarct. However, there is no diffusion restriction in the left parietal region , suggesting this infarct is of an older age.

Axial T1 C+ MR in a 1 year old with arteriopathy & subacute infarction shows gyriform enhancement of the cortical ribbon. Enhancement is common in the subacute phase of infarction. Precontrast T1 is necessary to distinguish true enhancement from the intrinsic ↑ T1 seen in cortical laminar necrosis.

Axial ADC map in the same patient shows modestly ↓ ADC within the affected cortex but resolution of acute gyral swelling, as evidenced by prominent sulci , suggesting the infarct is in the subacute phase.

Axial DWI MR in a 16-year-old boy involved in a motor vehicle collision (MVC) shows multiple small foci of diffusion restriction , consistent with small infarcts. Multiple infarcts should raise concern for dissection, especially when confined to a single arterial territory.

Axial CTA in the same patient shows vessel wall irregularity & an intimal flap in the left internal carotid artery (ICA) . The right ICA is small & showed areas of irregularity on other images (not shown). The findings are consistent with bilateral ICA dissections.

Additional Images

Axial T1 C+ MR in a 2-year-old girl shows cortical enhancement in the region of a right frontoparietal infarct, suggesting that it is at least a week old.

Axial TOF MRA in a 2 year old with multiple infarcts of various ages shows multiple tiny foci of flow-related signal in the bilateral thalami . This appearance is consistent with lenticulostriate collaterals of moyamoya-type vasculopathy in the setting of bilateral carotid terminus occlusions.

Axial T2 MR in a high school football player who developed vomiting, confusion, & vertigo during a game shows gyral swelling & hyperintense signal in the medial temporal lobe , which is in the vascular territory of the left posterior cerebral artery. Intracranial MRA acquired at the same time showed a small embolus in the left posterior cerebral artery (PCA).

Axial CTA of the cervical arteries in the same patient shows a subtle linear filling defect consistent with an intimal flap in the left vertebral artery.

Axial NECT in a 2 day old with congenital heart disease & seizures shows a well-defined, wedge-shaped region of decreased attenuation corresponding to the left MCA vascular territory, consistent with an acute/subacute arterial ischemic stroke.

Axial T1 C+ MR in an 8 year old with a history of neurofibromatosis type 1 & known bilateral carotid terminus occlusions (resulting in a moyamoya-type vasculopathy pattern) shows abnormal sulcal enhancement (climbing ivy sign) due to arterial collaterals distal to a proximal occlusion.

Note the segment of the insular cortical ribbon that is no longer visible on this axial NECT in a 9 year old with acute right hemiparesis. This subtle finding may be the 1st indicator of an acute stroke.

Axial T1 C+ MR shows the typical climbing ivy pattern of arterial collateral enhancement in distal territories caused by proximal occlusion from a moyamoya-type vasculopathy. Note the white matter infarct on left .

Axial DWI MR in the same child shows an acute infarct on the right with T2 shine-through in an old left-sided stroke .

Coronal T2 MR shows multiple areas of infarction resulting from left hemisphere herniation. Secondary infarction from herniation can cause more morbidity than the initial insult.

Axial DWI MR shows a characteristic "watershed" distribution of infarction in the right cerebral hemisphere. This infarct was the result of a carotid terminus stenosis that developed from bacterial meningitis & vasculitis.

Axial NECT in a 14-year-old boy with acute right hemiparesis shows a hyperdense MCA sign , indicating acute thrombus in a proximal middle cerebral artery branch.

Coronal FLAIR MR in the same patient shows edema in the insular cortex & frontal operculum supplied by the affected MCA branch . The patient had complete recovery without direct treatment, & no etiology was found.

Axial FLAIR MR in a 13-year-old girl with seizures after using ephedra shows foci of increased cortical & subcortical white matter signal in the right PCA & left superior cerebellar artery distributions .

Sagittal oblique volume-rendered MRA in the same child shows multiple foci of arterial narrowing & dilation due to a primary arteritis of the CNS.

Axial CECT shows a subtle linear filling defect in the left ICA of a child presenting with a left hemisphere infarct after mandibular surgery. The defect represents an arterial dissection.

Axial T2 MR shows predominately cortical/subcortical swelling & abnormal signal of the left parietal lobe, typical of a subacute left MCA territory infarct. ~ 1/3 of childhood strokes will not have an underlying etiology diagnosed.

Axial DWI MR in a 17-year-old girl shows a geographic area of diffusion restriction in the right insular region, consistent with an infarct. Work-up revealed a hypercoagulable state (antiphospholipid antibody).

Axial ADC map in a 17-year-old girl shows a geographic area of diffusion restriction in the right insular region, consistent with an infarct. Work-up revealed a hypercoagulable state (antiphospholipid antibody).

Axial FLAIR MR in a 2-year-old girl shows multiple areas of cytotoxic edema in both cerebral hemispheres in this patient with moyamoya-type vasculopathy.

Axial T2WI MR shows a small, periventricular infarct in a 6 month old. MRA revealed left carotid aneurysm. Proximal arterial pathology should always be investigated at presentation.

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KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

Diagnostic Checklist

TERMINOLOGY

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Morphology

CT Findings

NECT

CECT

CTA

MR Findings

Ultrasonographic Findings

Grayscale ultrasound

Color Doppler

Angiographic Findings

Nuclear Medicine Findings

Imaging Recommendations

Best imaging tool

Protocol advice

DIFFERENTIAL DIAGNOSIS

Seizure-Related Injury

MELAS

PATHOLOGY

General Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Demographics

Age

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls

References

Selected References

Images

Selected Images

Additional Images

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