Overall, presumptive risk factors for arterial ischemic stroke differ in children compared with adults. Whereas adult risk factors are primarily related to arrhythmias and obstructive atherosclerotic arteriopathies, these are rarely thought to be related to stroke in children. Also in contrast to adults, socioeconomic status has not been shown to be associated with an increased stroke risk in children [
2]. Interestingly, just as gender differences are found in adult stroke studies, several pediatric studies have shown a male predominance in children with a stroke [
2,
3]. Among boys, elevated testosterone levels were independently associated with stroke risk [
4]. The mechanism of this association is still unknown. In the International Pediatric Stroke Study (IPSS) and other studies of pediatric stroke, a wide range of underlying systemic factors were reported in the setting of childhood stroke, particularly sickle cell disease, cardiac disorders, trauma, and major infections such as meningitis, sepsis, and encephalitis [
2]. However, in the majority of the children, no underlying systemic disease is found. With advances in neuroimaging, cerebral arteriopathies are increasingly recognized as one of the major causes of childhood stroke in otherwise healthy children [
6,
7•]. Although the importance of arteriopathies is highlighted in this review, advances in understanding of sickle cell disease, cardiac disease, and prothrombotic disorders are also discussed.
Arteriopathies are an Important Underlying Cause of Childhood Arterial Ischemic Stroke
The IPSS recently reported on presumptive risk factors in their case series of 667 children from five continents that have had a stroke [
5]. In the study, 53% of the children who had vascular imaging were found to have an arteriopathy [
7•]. Some arteriopathies are due to well-recognized causes such as arterial dissection, moyamoya syndrome or disease, connective tissue disorders, and sickle cell disease. Late effects of radiation to the head and neck in childhood cancer survivors have also been associated with stroke due to cerebrovascular disease, and children with neurofibromatosis can have complications of a cerebral arteriopathy [
8]. However, in up to 30% of children presenting with a first arterial ischemic stroke, a focal arterial stenosis is identified but none of the classic underlying causes are discovered.
The term “transient cerebral arteriopathy” (TCA) was first used to describe a common course of cerebrovascular pathology in a group of children with ischemic stroke who received serial imaging studies [
9]. In this group, focal stenoses or segmental narrowing of the cerebral arterial wall, characteristically involving the distal internal cerebral artery, proximal middle cerebral artery, and sometimes the proximal anterior cerebral artery, were followed over time with serial angiograms (Fig. ). The term “transient” was used because of the monophasic progression of cerebrovascular disease. In children with TCA, the arterial stenosis and narrowing is strictly unilateral and may initially worsen. In some cases, no abnormality is noted on initial vascular imaging, but stenosis or occlusion is seen on follow-up imaging within the first few months. However, after the first 6 months, the arteriopathy stabilizes and sometimes improves. In some sense, the term “transient” cerebral arteriopathy is somewhat misleading. Although monophasic in the progression of stenosis, in many cases the arterial narrowing persists on long-term follow-up imaging.
On initial imaging studies, TCA cannot be distinguished from a progressive arteriopathy such as moyamoya disease or a vasculitis that presents unilaterally. Worsening after 6 months or bilateral involvement suggests an arteriopathy other than TCA, with a different course and prognosis. In recognition of the limitations of classifying arteriopathies on initial imaging, the IPSS has recently suggested the term “focal cerebral arteriopathy” of childhood (FCA) to describe children with unilateral arterial stenosis without an apparent underlying cause at presentation [
7•]. Both the terms TCA and FCA are simply descriptive and do not imply a specific pathophysiology; however, these arteriopathies are clinically important because they indicate an increased risk for recurrent stroke [
6,
10,
11]. In all children who have had a stroke, vascular imaging of intracranial and neck vessels is imperative to detect arteriopathies, with magnetic resonance angiography (MRA) as the preferred modality. However, if interventional neuroradiologists who have an expertise in pediatrics are available, conventional angiography can be considered in cases in which diagnosis remains unclear on MRA. In addition, even in children with a stable clinical course, MRI and vascular imaging should be repeated 3–6 months after the acute stroke and again 1 year later to detect development of or changes in arteriopathies, as well as to look for new subclinical infarcts.
Recent Infection is a Risk Factor for Focal Cerebral Arteriopathy in Childhood
Currently, the underlying mechanisms for these unilateral, monophasic arteriopathies are poorly understood, and studies are ongoing to elucidate their pathophysiology. The role of infection as a part of the underlying vascular pathology is of particular current interest. The link between childhood stroke and infection was first noted because of its temporal association with varicella infection; post-varicella angiopathy has been well described as a cause for ischemic stroke in both adults and children [
12,
13]. Importantly, no association has been found with varicella vaccination [
14]. Multiple viruses other than varicella have been linked to case reports of arteriopathies and stroke in children. Strengthening the infectious hypothesis, the IPSS reported finding an association between childhood arteriopathies and recent minor infections in their large cohort of children with ischemic stroke [
7•]. In the study, 25% of the children were classified as having FCA, higher in frequency than either moyamoya (22%) or dissection (20%). Predictors of overall arteriopathies were early school age (5–9 years), recent upper respiratory infections, and sickle cell disease. The only predictor of FCA was a recent upper respiratory infection (odds ratio [OR]

=

2.1; 95% CI, 1.01–4.38). The role of minor infections in the pathogenesis of stroke has been suggested either as a cause of direct vascular injury, or by inducing a systemic prothrombotic state, or through both mechanisms. However, minor infections are extremely common in young children, and yet most children do not have strokes. More study is needed to clarify how infection contributes to arteriopathies and stroke.
Transcranial Doppler Screening Effectively Reduces Stroke Risk in Children with Sickle Cell Disease, but Barriers to Care Persist
Children with sickle cell disease comprise another important group with a high risk of arteriopathies and stroke. Prior to modern primary prevention strategies, up to 11% of children with sickle cell anemia had a clinical stroke by the age of 20 years [
15]. In 1992, transcranial Doppler (TCD) was found to be effective in identifying patients with sickle cell disease at high risk for stroke [
16]. The Stroke Prevention Trial in Sickle Cell Anemia (STOP) established that chronic transfusion decreased the risk of stroke by 90% in children with abnormal TCD results [
17], leading to recommendations for chronic transfusion for prevention of stroke in children deemed at high risk. However, TCD screening in sickle cell disease continues to be examined for feasibility and efficacy internationally [
18,
19], and barriers to care persist. A recent study of children in northern California showed the rate of stroke in children with sickle cell disease has dropped by more than half the rate prior to 1998, but also demonstrated that children living farther from a vascular laboratory are less likely to be screened [
20]. Finally, although stroke risk in people with sickle cell disease is usually attributed to red cell sickling and vasculopathy of large intracranial vessels, new concerns have recently been raised for an increased risk for cardioembolic stroke in these children because of the potential for increased right heart pressure and right-to-left shunting in the setting of a prothrombotic state [
21].This suggests the intracardiac shunts in children with sickle cell disease should be further studied as a potentially modifiable cause of stroke. Current American Heart Association stroke prevention screening recommendations in sickle cell disease are for annual TCD monitoring of children with normal TCD velocities (≤170 cm/s), with consideration of more frequent monitoring in children 2 to 10 years of age. Children with velocities elevated to ≥200 cm/s should be restudied in 1 month, and studies with borderline or mildly abnormal results should be repeated in 3–6 months. Periodic transfusions to reduce the percentage of sickle hemoglobin are recommended in children with abnormal TCD results [
22••].
Complex Congenital Heart Disease Presents Risk for Stroke in the Peri-Operative Period, but Stroke Risk Persists for Many Years After Surgery
Congenital heart disease and other cardiac problems are still recognized as presumed risk factors for childhood stroke because of their high frequency in case series [
2]. A case-control study of children in northern California demonstrated an increased risk for children with congenital heart disease requiring surgical repair (OR

=

11; 95% CI, 3.1–39.4) (Fox and Fullerton, unpublished data). Even with modern surgical techniques, the peri-operative period may be of particularly high risk, as demonstrated in a recent series of 122 children undergoing open heart surgery, which identified stroke in 10% [
22••]. However, children with complex congenital heart disease remain at risk for years after their last surgery, which reflects increased stroke risk from the heart disease itself. When feasible, complex congenital heart lesions should be repaired to improve cardiac function and reduce the risk of subsequent stroke [
22••].
Prothrombotic Disorders Increase the Risk of Stroke in the Setting of Additional Risk Factors
Finally, controversies remain over the strength of association of hypercoaguable disorders as a risk for childhood stroke. Homozygosity for MTHFR C677T polymorphism did not show an increased risk for arterial ischemic stroke in two recent studies of stroke in children in the United States [
24] and Croatia [
25], but a study in Poland [
26] found a threefold increased risk of stroke with the presence of the MTHFR C677T allele. Factor V G1691A was associated with a sevenfold increased risk among children with stroke in the Croatian study [
25]. Although various coagulation abnormalities have been reported in children after stroke, most pediatric stroke experts believe the likelihood of stroke from most prothrombotic states seems to be relatively low. However, the risk may tend to increase in the setting of additional risk factors. Children with a stroke who are found to have a prothrombotic polymorphism or other prothrombotic state should have additional workup including serial vascular imaging to determine etiology. Although there are no class I recommendations regarding hypercoaguable states in childhood stroke, it is reasonable to evaluate for elevated serum homocysteine levels and the more common prothrombotic states, and start folate, vitamin B
6, or vitamin B
12 if homocysteine is found to be elevated. It is also reasonable to discontinue oral contraceptives in adolescents after an ischemic or thrombotic stroke [
22].