Diffusion and perfusion magnetic resonance imaging in childhood stroke

Imaging of Suspected Stroke in Children, From the AJR Special Series on Emergency Radiology

Pediatric stroke encompasses different causes, clinical presentations, and associated conditions across ages. Although it is relatively uncommon, pediatric stroke presents with poor short- and long-term outcomes in many cases. Because of a wide range of overlapping presenting symptoms between pediatric stroke and other more common conditions, such as migraine and seizures, stroke diagnosis can be challenging or delayed in children. When combined with a comprehensive medical history and physical examination, neuroimaging plays a crucial role in diagnosing stroke and differentiating stroke mimics. This review highlights the current neuroimaging workup for diagnosing pediatric stroke in the emergency department, describes advantages and disadvantages of different imaging modalities, highlights disorders that predispose children to infarct or hemorrhage, and presents an overview of stroke mimics. Key differences in the initial approach to suspected stroke between children and adults are also discussed.

Pediatric Headache in Primary Care and Emergency Departments: Consensus with RAND/UCLA Method

Headache is the most frequent neurological symptom in childhood and the main reason for admission to pediatric emergency departments. The aim of this consensus document is to define a shared clinical pathway between primary care pediatricians (PCP) and hospitals for the management of children presenting with headache. For the purposes of the study, a group of hospital pediatricians and a group of PCP from the Emilia Romagna’s health districts were selected to achieve consensus using the RAND/UCLA appropriateness method. Thirty-nine clinical scenarios were developed: for each scenario, participants were asked to rank the appropriateness of each option from 1 to 9. Agreement was reached if ≥75% of participants ranked within the same range of appropriateness. The answers, results, and discussion helped to define the appropriateness of procedures with a low level of evidence regarding different steps of the diagnostic-therapeutic process: primary care evaluation, emergency department evaluation, hospital admission, acute therapy, prophylaxis, and follow-up. The RAND proved to be a valid method to value appropriateness of procedures and define a diagnostic-therapeutic pathway suitable to the local reality in the management of pediatric headache. From our results, some useful recommendations were developed for optimizing the healthcare professionals’ network among primary care services and hospitals.

Harnessing Neuroimaging Capability in Pediatric Stroke: Proceedings of the Stroke Imaging Laboratory for Children Workshop

On June 5, 2015 the International Pediatric Stroke Study and the Stroke Imaging Laboratory for Children cohosted a unique workshop focused on developing neuroimaging research in pediatric stroke. Pediatric neurologists, neuroradiologists, interventional neuroradiologists, physicists, nurse practitioners, neuropsychologists, and imaging research scientists from around the world attended this one-day meeting. Our objectives were to (1) establish a group of experts to collaborate in advancing pediatric neuroimaging for stroke, (2) develop consensus clinical and research magnetic resonance imaging protocols for pediatric stroke patients, and (3) develop imaging-based research strategies in pediatric ischemic stroke. This article provides a summary of the meeting proceedings focusing on identified challenges and solutions and outcomes from the meeting. Further details on the workshop contents and outcomes are provided in three additional articles in the current issue of Pediatric Neurology.

Paradoxical centrally increased diffusivity in perinatal arterial ischemic stroke

BACKGROUND

Restricted diffusion on acute MRI is the diagnostic standard for perinatal arterial ischemic stroke. In a subset of children with perinatal arterial ischemic stroke, primarily those with large infarct volumes, we noted a core of centrally increased diffusivity with a periphery of restricted diffusion.

OBJECTIVE

Given the paradoxical diffusion-weighted imaging (DWI) appearance observed in some children with perinatal arterial ischemic stroke, we sought to determine its significance and hypothesized that: (1) centrally increased diffusivity is associated with larger infarcts in perinatal arterial ischemic stroke and (2) this tissue is irreversibly injured (infarcted).

MATERIALS AND METHODS

We reviewed all perinatal arterial ischemic stroke cases in a prospective cohort study from Aug. 1, 2000, to Jan. 1, 2012. Infarct volumes were measured by drawing regions of interest around the periphery of the area of restricted diffusion on DWI. The Mann-Whitney U test was used to compare means between groups.

RESULTS

Of 25 eligible cases, centrally increased diffusivity was seen in 4 (16%). Cases with centrally increased diffusivity had larger average infarct volumes (mean 117,182 mm(3) vs. 36,995 mm(3); P = 0.008), higher average apparent diffusion coefficient (ADC) values in the infarct core (1,679 × 10(-6) mm(2)/s vs. 611 × 10(-6) mm(2)/s, P < 0.0001), and higher ADC ratio (1.2 vs. 0.5, P < 0.0001). At last clinical follow-up, children with perinatal arterial ischemic stroke and centrally increased diffusivity were more often treated for ongoing seizures (75% vs. 0%; P < 0.001) than those without.

CONCLUSION

Centrally increased diffusivity was associated with larger stroke volume and the involved tissue was confirmed to be infarcted on follow-up imaging. Radiologists should be aware of this unusual appearance of perinatal arterial ischemic stroke in order to avoid underestimating infarct volume or making an incorrect early diagnosis.

Paediatric arterial ischemic stroke: acute management, recent advances and remaining issues

Stroke is a rare disease in childhood with an estimated incidence of 1-6/100.000. It has an increasingly recognised impact on child mortality along with its outcomes and effects on quality of life of patients and their families. Clinical presentation and risk factors of paediatric stroke are different to those of adults therefore it can be considered as an independent nosological entity. The relative rarity, the age-related peculiarities and the variety of manifested symptoms makes the diagnosis of paediatric stroke extremely difficult and often delayed. History and clinical examination should investigate underlying diseases or predisposing factors and should take into account the potential territoriality of neurological deficits and the spectrum of differential diagnosis of acute neurological accidents in childhood. Neuroimaging (in particular diffusion weighted magnetic resonance) is the keystone for diagnosis of paediatric stroke and other investigations might be considered according to the clinical condition. Despite substantial advances in paediatric stroke research and clinical care, many unanswered questions remain concerning both its acute treatment and its secondary prevention and rehabilitation so that treatment recommendations are mainly extrapolated from studies on adult population. We have tried to summarize the pathophysiological and clinical characteristics of arterial ischemic stroke in children and the most recent international guidelines and practical directions on how to recognise and manage it in paediatric emergency.

Susceptibility-weighted imaging in pediatric arterial ischemic stroke: a valuable alternative for the noninvasive evaluation of altered cerebral hemodynamics

BACKGROUND AND PURPOSE

SWI provides information about blood oxygenation levels in intracranial vessels. Prior reports have shown that SWI focusing on venous drainage can provide noninvasive information about the degree of brain perfusion in pediatric arterial ischemic stroke. We aimed to evaluate the influence of the SWI venous signal pattern in predicting stroke evolution and the development of malignant edema in a large cohort of children with arterial ischemic stroke.

MATERIALS AND METHODS

A semiquantitative analysis of venous signal intensity on SWI and diffusion characteristics on DTI was performed in 16 vascular territories. The mismatch between areas with SWI-hypointense venous signal and restricted diffusion was correlated with stroke progression on follow-up. SWI-hyperintense signal was correlated with the development of malignant edema.

RESULTS

We included 24 children with a confirmed diagnosis of pediatric arterial ischemic stroke. Follow-up images were available for 14/24 children. MCA stroke progression on follow-up was observed in 5/6 children, with 2/8 children without mismatch between areas of initial SWI hypointense venous signal and areas of restricted diffusion on DTI. This mismatch showed a statistically significant association (P = .03) for infarct progression. Postischemic malignant edema developed in 2/10 children with and 0/14 children without SWI-hyperintense venous signal on initial SWI (P = .07).

CONCLUSIONS

SWI-DTI mismatch predicts stroke progression in pediatric arterial ischemic stroke. SWI-hyperintense signal is not useful for predicting the development of malignant edema. SWI should be routinely added to the neuroimaging diagnostic protocol of pediatric arterial ischemic stroke.

The course of apparent diffusion coefficient values following perinatal arterial ischemic stroke

BACKGROUND

Diffusion weighted MR imaging (DWI) plays an important role in the diagnosis of perinatal arterial ischemic stroke (PAIS) during the acute phase. Its derived apparent diffusion coefficient (ADC) can be used to quantify the diffusion restriction. Aim of the current study was to identify the changes in ADC values in the acute phase following PAIS.

METHODS

A cohort of 36 infants with a confirmed PAIS who were examined once during the first ten days of life was studied. ADC values in the core of the ischemic tissue (iADC) were determined and correlated with postnatal age. ADC ratios (rADC) were calculated by dividing the iADC value by the ADC value of the corresponding area in the contralateral 'healthy' hemisphere.

RESULTS

Infants were scanned between days two and ten. A non-linear increase in iADC and rADC values was observed over time and large middle cerebral artery strokes resulted in lower iADC and rADC values. Normalisation of rADC values was observed after day seven. rADC values were lower when compared to previously published rADC values of infants with hypoxic ischemic encephalopathy, suggesting more severe injury.

CONCLUSIONS

Following PAIS, DWI showed decreased ADC values with a non-linear increase during the first week, and pseudonormalization after day 7, which limits the use of DWI to assess PAIS to the first week. Compared to previous studies, ADC values were lower when compared to infants with hypoxic ischemic encephalopathy, most likely due to more severe injury.

Ischemic stroke in infants and children: practical management in emergency

Stroke is a rare disease in children, with an estimated incidence 13/100000 and a significant impact on morbidity and mortality. Clinical presentation and risk factors, present in almost half of pediatric patients, are not the same as in adults. The diagnosis of stroke in children is often delayed because signs and symptoms can be subtle and nonspecific. History and clinical examination should exclude underlying diseases or predisposing factors. Neuroimaging is crucial in defining diagnosis. Other tests might be necessary, according to the clinical picture. We present here the most recent practical directions on how to diagnose and manage arterial stroke in children, according to different international guidelines on the subject.

Pediatric arterial ischemic stroke

Arterial ischemic stroke (AIS) is a rare disorder in children. Research suggests that risk factors, outcomes, and presentation are different from those of adult stroke. In particular, prothrombotic abnormalities and large vessel arteriopathies that are nonatherosclerotic seem to play a large role in the pathogenesis of childhood AIS. This review examines the epidemiology and etiologies of neonatal and childhood AIS and provides a detailed discussion of approaches to the clinical characterization, diagnostic evaluation, and management. Long-term outcomes of recurrent AIS and neuromotor, speech, cognitive, and behavioral deficits are considered. Emphasis is on evidence underlying current knowledge and key questions for further investigation.

Neuroimaging in assessment of risk of stroke in children with sickle cell disease

PURPOSE

Stroke and subclinical "silent infarcts" are major causes of morbidity in children with Sickle Cell Disease (SCD). Ischemic strokes are more common in younger children while hemorrhagic strokes are more frequent in adults. The goal of neuroimaging in acute stroke is to document whether the stroke is ischemic or hemorrhagic, to assess the extent of parenchymal abnormalities and to determine the presence of other cerebrovascular lesions. Computed Tomography (CT) is the primary modality for the assessment of acute stroke patients because of its 24/7 availability and ability to exclude hemorrhagic causes. Magnetic resonance imaging (MRI) and MR angiography (MRA) are recommended to determine precisely extent of infarction and detect cerebrovascular abnormalities. The goal of neuroimaging in patients with hemorrhagic stroke is to identify an arteriovenous malformation or aneurysm(s) amenable to surgery or catheter intervention.The risk of first stroke is very high in asymptomatic children with intracranial arterial mean velocities over 200 cm/s on transcranial Doppler (TCD) examination. The risk can be substantially reduced if chronic blood transfusions are timely implemented. Large cerebral vessel disease detected by TCD can be confirmed or excluded by MRI/MRA. Those with evidence of parenchymal and/or cerebrovascular lesions should be followed by preventive therapy. In patients with neurologic symptoms and negative MRI/MRA findings Positron Emission Tomography or single photon emission CT is recommended. There are no specific neuroimaging findings that suggest that blood transfusions can be safely halted in children with SCD.

MRI in paediatric hypoxic-ischemic disease, metabolic disorders and malformations-a review

MRI has become the most important modality in paediatric neuroimaging. It provides an excellent anatomical overview with good spatial and temporal resolution, allows investigations of the blood vessels, and - using technologies such as diffusion-weighted imaging and magnetic resonance spectroscopy - it allows quick and exact differentiation of ischemic, hypoxic, inflammatory, oncologic, traumatic and metabolic diseases. This review presents an overview of brain MRI in infants and children with suspected hypoxic-ischemic disease, metabolic disorders or (vascular) malformations, illustrating these issues by some MRI findings in selected important conditions and discussing some major clinical and pathophysiological aspects important for imaging.

Pediatric arterial ischemic stroke

Arterial ischemic stroke (AIS) is a rare disorder in children. Research suggests that risk factors, outcomes, and presentation are different from those of adult stroke. In particular, prothrombotic abnormalities and large vessel arteriopathies that are nonatherosclerotic seem to play a large role in the pathogenesis of childhood AIS. This review examines the epidemiology and etiologies of neonatal and childhood AIS and provides a detailed discussion of approaches to the clinical characterization, diagnostic evaluation, and management. Long-term outcomes of recurrent AIS and neuromotor, speech, cognitive, and behavioral deficits are considered. Emphasis is on evidence underlying current knowledge and key questions for further investigation.

Diffusion-weighted imaging findings on MRI as the sole radiographic findings in a child with proven herpes simplex encephalitis

We present a case of herpes simplex encephalitis in an 8-year-old girl, in whom hyperintensity was detected on diffusion-weighted imaging (DWI) while conventional MRI sequences were normal 1 week after the onset of neurological symptoms. This case is rare in that a child beyond the neonatal period with focal herpes simplex encephalitis had an abnormal DWI sequence as the only MRI finding.

Arterial ischemic stroke in children

Stroke in children is relatively rare. Advances in the clinical recognition and radiographic diagnosis of ischemic stroke have increased the frequency of the diagnosis in infants and children and have raised the need for immediate therapy. A vast amount of data has recently become available through basic research and neuroimaging techniques shedding new light on the chain of events that occur in ischemic stroke in animal models and in the adult population. Whether this new information can also be applied to the pediatric population remains to be seen, but it is likely that the active management of children with acute ischemic stroke in the near future will include brain protection, brain reperfusion, and prevention measures.

Arterial ischemic stroke in childhood: risk factors and outcome in old versus new era

Risk factors of children with arterial ischemic stroke were retrospectively evaluated. The children were grouped according to values on developing diagnostic tools: 13 in the old era (1987-1994) and 18 in the new era (1995-2004). The old era battery included 5 tests: protein C, protein S, antithrombin, lupus anticoagulants, and anticardiolipin antibodies. The new era battery added 5 more tests: homocystine level, factor VIII level, mutations for factor V Leiden and prothrombin G20210A, and lipoprotein (a) level. At least 1 risk factor was found in 5 of 13 children (38.5%) in the old era and in 8 of 18 (44.4%) in the new era. The extended battery for prothrombotic disorders revealed 7 risk factors in 4 children (22.2%) in the new era, whereas the limited battery identified a single risk factor in 1 child (7.7%) in the old era. For the correct etiologic identification, prothrombotic risk factors should be extensively evaluated in patients with arterial ischemic stroke.

Therapy Insight: stroke risk and its management in patients with sickle cell disease

Children with sickle cell disease, a chronic hemolytic anemia, present with a wide variety of neurological syndromes, including ischemic and hemorrhagic stroke, transient ischemic attacks, 'soft neurological signs', seizures, headache, coma, visual loss, altered mental status, cognitive difficulties, and covert or 'silent' infarction. Those with ischemic stroke usually have stenosis or occlusion of the distal internal carotid and proximal middle cerebral arteries. Indefinite transfusion prevents recurrence in most patients who have had a stroke, and can prevent first stroke in those with high transcranial Doppler velocities. High white cell count, low hemoglobin and oxyhemoglobin desaturation predict neurological complications. Other risk factors for overt ischemic stroke include hypertension, previous transient ischemic attack, covert infarction and chest crisis. For hemorrhagic stroke, aneurysms are common in adults but not children, who often present with hypertension after transfusion or corticosteroids. Seizures are particularly common in patients with cerebrovascular disease and covert infarction; the latter is also associated with hyposplenism and infrequent pain. Factors associated with cognitive difficulties include thrombocytosis, infarction, large-vessel disease, and perfusion abnormality on neuroimaging. As well as investigating the role of genes and the possibility that hydroxyurea or blood pressure control reduce neurological complications, we should explore the modifiable effects of poor nutrition, chronic infection, hemolysis and oxyhemoglobin desaturation on stroke risk.

Comparative prognostic utilities of early quantitative magnetic resonance imaging spin-spin relaxometry and proton magnetic resonance spectroscopy in neonatal encephalopathy

OBJECTIVE

We sought to compare the prognostic utilities of early MRI spin-spin relaxometry and proton magnetic resonance spectroscopy in neonatal encephalopathy.

METHODS

Twenty-one term infants with neonatal encephalopathy were studied at a mean age of 3.1 days (range: 1-5). Basal ganglia, thalamic and frontal, parietal, and occipital white matter spin-spin relaxation times were determined from images with echo times of 25 and 200 milliseconds. Metabolite ratios were determined from an 8-mL thalamic-region magnetic resonance spectroscopy voxel (1H point-resolved spectroscopy; echo time 270 milliseconds). Outcomes were assigned at age 1 year as follows: (1) normal, (2) moderate (neuromotor signs or Griffiths developmental quotient of 75-84), (3) severe (functional neuromotor deficit or developmental quotient <75 or died). Predictive efficacies for differentiation between normal and adverse (combined moderate and severe) outcomes were compared by receiver operating characteristic curve analysis and logistic regression.

RESULTS

Thalamic and basal ganglia spin-spin relaxation times correlated positively with outcome and predicted adversity. Although thalamic and basal ganglia spin-spin relaxation times were prognostic of adversity, magnetic resonance spectroscopy metabolite ratios were better predictors, and, of these, lactate/N-acetylaspartate was most accurate.

CONCLUSIONS

Deep gray matter spin-spin relaxation time was increased in the first few days after birth in infants with an adverse outcome. Proton magnetic resonance spectroscopy was more prognostic than spin-spin relaxation time, with lactate/N-acetylaspartate the best measure. Nevertheless, both techniques were useful for early prognosis, and the potential superior spatial resolution of spin-spin relaxometry may define better the precise anatomic pattern of injury in the early days after birth.

Stroke in children with sickle cell disease

Children with sickle disease are at high risk for ischemic stroke and transient ischemic attacks, usually secondary to intracranial arteriopathy involving the terminal internal carotid and proximal middle cerebral and anterior cerebral arteries, which may be diagnosed using transcranial Doppler ultrasound or magnetic resonance angiography (MRA). Other central nervous system (CNS) complications include seizures and coma, which may be secondary to ischemic stroke, sinovenous thrombosis, reversible posterior leukoencephalopathy, or acute demyelination. The immediate priority after an acute CNS event is to improve cerebral oxygenation with oxygen supplementation to maintain peripheral saturation measured using pulse oximetry between 96% and 99%, and a simple transfusion of packed cells within an hour of presentation if the patient's hemoglobin is less than 10 g/dL. The patient then should have erythrocytapheresis or manual exchange to reduce the hemoglobin S percentage to below 30%. Computed tomography to exclude hemorrhage is mandatory and MR T2-weighted imaging with MRA, fat-saturated imaging of the neck (dissection), MR venography (sinovenous thrombosis), and diffusion-weighted imaging usually distinguishes between arterial ischemic stroke and the differential diagnoses. Comatose patients with widespread focal or global cerebral edema may have good functional outcome after surgical decompression. Anticoagulation may be indicated for dissection or sinovenous thrombosis and steroids for demyelination. Blood pressure should be reduced slowly if raised in patients with reversible posterior leukoencephalopathy. Seizures should be treated aggressively and electroencephalogram monitoring should be done to exclude subclinical seizures if the patient is unconscious. Hemorrhagic stroke may require craniectomy and drainage and/or management of vasospasm. Interventional neuroradiology with coils is an alternative to surgical clipping for aneurysms. For secondary prevention, regular blood transfusion to hemoglobin S of less than 30% reduces the risk of recurrent stroke from approximately 67% to approximately 10%. Hydroxyurea and phlebotomy may be used in patients who are alloimmunized. Moyamoya syndrome is a risk factor for recurrence despite prophylactic blood transfusion. Revascularization may prevent additional stroke. Bone marrow transplantation may be offered to patients with human leukocyte antigen-compatible siblings. Blood transfusion prevents stroke in patients with velocities greater than 200 cm per second on TCD; a phase III trial studying the prevention of the progression of silent infarction is being done. Emerging primary prophylaxis regimens being tested include citrulline and arginine, aspirin, and overnight oxygen supplementation. Physicians caring for children with sickle cell disease also should ensure adequate nutrition, including five servings of fruit and vegetables a day. The role of vitamin supplementation is controversial, particularly when patients must take daily penicillin prophylaxis.

Stroke and the child's brain: an overview of epidemiology, syndromes and risk factors

Childhood stroke is emerging as a serious and frequent disorder. In contrast to adult stroke, the study of childhood stroke is in a very early stage of research development with no randomized controlled trials conducted to date outside of sickle cell stroke. The results of research in adults have limited applicability to children with stroke due to fundamental age-related differences in the neurological, cerebrovascular and coagulation systems. In recent years clinical and basic research studies have improved our understanding of childhood stroke. Population-based studies have resulted in an increased awareness of the frequencies and features of stroke syndromes in children. Cohort and case-control studies have led to an enhanced understanding of the multiple risk factors underlying childhood stroke. Advances in neuroimaging and in genetic and other laboratory testing approaches have resulted in an increased definition of stroke subtypes and risk factors.

Changes in brain water diffusion during the 1st year of life

PURPOSE

To evaluate the normal water diffusion changes that occur during the 1st year of life.

MATERIALS AND METHODS

Diffusion-weighted imaging was performed in 40 subjects (age range, birth to 1 year) in whom both magnetic resonance imaging and neurologic assessment results were normal at the time of imaging and, where available, at follow-up. Apparent diffusion coefficient (ADC) was calculated in four areas of white matter (anterior and posterior subcortical and internal capsule) and four of gray matter (cortex, thalamus, head of the caudate nucleus, and lentiform nucleus). Linear regression was used to examine the effect of age on ADC, and analysis of variance was used to compare ADC within different brain regions.

RESULTS

ADC decreased with age in all regions (P <.01). Data best fit with a logarithmic decline (r(2) = 0.20-0.63). ADC was significantly higher in white (113 x 10(-5) mm(2)/sec) than in gray matter (102 x 10(-5) mm(2)/sec; P <.001). Significant differences were seen among three white matter regions (subcortical, 188 x 10(-5) mm(2)/sec at birth; anterior limb of internal capsule, 130 x 10(-5) mm(2)/sec; posterior limb of internal capsule, 109 x 10(-5) mm(2)/sec) and three gray matter regions (cortex, 134 x 10(-5) mm(2)/sec at birth; head of caudate nucleus, 134 x 10(-5) mm(2)/sec at birth; and thalamus and lentiform nucleus, 120 x 10(-5) mm(2)/sec; P <.01).

CONCLUSION

Results suggest that in neonates and infants, water diffusion is highly dependent on both subject age and brain location.

Report of the National Institute of Neurological Disorders and Stroke workshop on perinatal and childhood stroke

The National Institute of Neurological Disorders and Stroke and the Office of Rare Disorders sponsored a workshop on perinatal and childhood stroke in Bethesda, Maryland, on September 18 and 19, 2000. This was an international workshop to bring together experts in the field of perinatal and childhood stroke. Topics covered included epidemiology, animal models, risk factors, outcome and prognosis, and areas of future research for perinatal and childhood stroke. Stroke in infants and children is an important cause of morbidity and mortality and an emerging area for clinical and translational research. Currently, there is no consensus on the classification, evaluation, outcome measurement, or treatment of perinatal and childhood stroke. Pediatric stroke registries are needed to generate data regarding risk factors, recurrence, and outcome. The impact of maternal and perinatal factors on risk and outcome of neonatal stroke needs to be studied. This information is essential to identifying significant areas for future treatment and prevention.

Nocturnal hypoxaemia and central-nervous-system events in sickle-cell disease

BACKGROUND

Central-nervous-system (CNS) events, including strokes, transient ischaemic attacks, and seizures are common in sickle-cell disease. Stroke can be predicted by high velocities in the internal-carotid or middle-cerebral arteries on transcranial doppler ultrasonography. We tested the hypothesis that nocturnal hypoxaemia can predict CNS events better than clinical or haematological features, or transcranial doppler sonography.

METHODS

We screened 95 hospital-based patients with sickle-cell disease (median age 7.7 years [range 1.0-23.1]), but without previous stroke, with transcranial doppler and overnight pulse oximetry. Follow-up continued for a median of 6.01 (0.11-8.54) years.

FINDINGS

19 patients had CNS events (six ischaemic and one haemorrhagic stroke, eight transient ischaemic attacks, and four seizures). Mean overnight oxygen saturation ([SaO(2)] hazard ratio 0.82 per 1% increase [95% CI 0.71-0.93]; p=0.003) and higher internal-carotid or middle-cerebral artery velocity (1.02 for every increase of 1 cm/s [1.004-1.03]; p=0.009) were independently associated with time to CNS event. After accounting for mean SaO(2), artery velocity, and haemoglobinopathy, high haemoglobin concentration was also associated with an increased risk of CNS event (1.7 per g/dL, [1.18-2.43]; p=0.004). Dips suggestive of obstructive sleep apnoea did not predict CNS events, and adenotonsillectomy seemed to have no effect, although the CI were wide and clinically important effects cannot be excluded.

INTERPRETATION

Screening for, and appropriate management of, nocturnal hypoxaemia might be a safe and effective alternative to prophylactic blood transfusion for primary prevention of CNS events in sickle-cell disease.

Etiology of stroke in children

Although the risk factors for stroke in children are numerous and differ greatly from the causes of stroke in adults, a thorough diagnostic evaluation can identify one or more risk factors in most patients. Cardiac disorders and hemoglobinopathy are the most common causes of ischemic infarction, whereas various congenital anomalies of the blood vessels or defects in coagulation or platelet function are often found in children with intraparenchymal hemorrhage. More than one risk factor is commonly identified, especially in children with dural venous thrombosis. Identification of the underlying risk factors for cerebrovascular disorders in children is important because many of the risk factors can be treated, reducing the risk of subsequent strokes.