Quantitative MRI of the brain in children with sickle cell disease reveals abnormalities unseen by conventional MRI

Neuroimaging and Cognitive Function in Sickle Cell Disease: A Systematic Review

Sickle cell disease (SCD) is the most common inherited single-gene disease. Complications include chronic anaemia, reduced oxygen-carrying capability, and cerebral vasculopathy, resulting in silent cerebral infarction, stroke, and cognitive dysfunction with impairments in measures of executive function, attention, reasoning, language, memory, and IQ. This systematic review aims to investigate the association between neuroimaging findings and cognition in children with SCD. Searches of PubMed and Embase were conducted in March 2022. Studies were included if participants were <18 years, if original data were published in English between 1960 and 2022, if any genotype of SCD was included, and if the relationship between cognition and neuroimaging was examined. Exclusion criteria included case studies, editorials, and reviews. Quality was assessed using the Critical Appraisal Skills Programme Case Control Checklist. A total of 303 articles were retrieved; 33 met the eligibility criteria. The presence of overt or silent strokes, elevated blood flow velocities, abnormal functional connectivity, and decreased fMRI activation were associated with neuropsychological deficits in children with SCD when compared to controls. There is a critical need to address the disease manifestations of SCD early, as damage appears to begin at a young age. Most studies were cross-sectional, restricting the interpretation of the directionality of relationships. Future research employing longitudinal neuroimaging and neuropsychological assessments could improve our understanding of the cumulative consequences of SCD on the developing brain.

Neuronal injuries in cerebral infarction and ischemic stroke: From mechanisms to treatment (Review)

Stroke is the leading cause of disabilities and cognitive deficits, accounting for 5.2% of all mortalities worldwide. Transient or permanent occlusion of cerebral vessels leads to ischemic strokes, which constitutes the majority of strokes. Ischemic strokes induce brain infarcts, along with cerebral tissue death and focal neuronal damage. The infarct size and neurological severity after ischemic stroke episodes depends on the time period since occurrence, the severity of ischemia, systemic blood pressure, vein systems and location of infarcts, amongst others. Ischemic stroke is a complex disease, and neuronal injuries after ischemic strokes have been the focus of current studies. The present review will provide a basic pathological background of ischemic stroke and cerebral infarcts. Moreover, the major mechanisms underlying ischemic stroke and neuronal injuries are summarized. This review will also briefly summarize some representative clinical trials and up-to-date treatments that have been applied to stroke and brain infarcts.

A Traditional Review of Sickle Cell Disease and the Associated Onset of Dementia: Hematological and Neurocognitive Crossroads

Sickle cell trait and disease are potential risk factors for dementia and cognitive dysfunction in African Americans, as are genetic variants. This illness affects around 300 million people globally. Due to its ability to defend against severe malaria, it represents an evolutionary survival advantage. It has been shown that sickle cell disease and trait are independent risk factors for the prevalence and incidence of albuminuria and chronic renal disease. Sickle cell anemia impairs cognitive performance in people with minimal or mild manifestations of the genetic blood disorder, owing mostly to its cerebrovascular implications. Similarly, various cerebral minor vascular disorders, such as silent cerebral infarcts, have been linked to the sickle cell trait, which is associated with impaired cognitive ability. It has been found that patients with sickle cell disease have a significantly decreased subcortical and cortical brain volume. Adults and children with sickle cell disease have been documented to have attention-related issues, particularly reduced sustained attention.

Stroke and presence of patent foramen ovale in sickle cell disease

Sickle cell disease (SCD) is an inherited monogenic hemoglobinopathy characterized by formation of sickle erythrocytes under conditions of deoxygenation. Sickle erythrocytes can lead to thrombus formation and vaso-occlusive episodes that may result in hemolytic anemia, pain crisis and multiple organ damage. Moreover, SCD is characterized by endothelial damage, increased inflammatory response, platelet activation and aggravation, and activation of both the intrinsic and the extrinsic coagulation pathways. Cerebrovascular events constitute an important clinical complication of SCD. Children with SCD have a 300-fold higher risk of acute stroke and by the age of 45 about 25% of patients have suffered an overt stoke. Management and prevention of stroke in patients with SCD is not well defined. Moreover, the presence of patent foramen ovale (PFO) increases the risk of the occurrence of an embolic cerebrovascular event. The role of PFO closure and antiplatelet or anticoagulation therapy has not been well investigated. Moreover, during COVID-19 pandemic and taking into account the increased rates of thrombotic events and the difficulties in blood transfusion, management of SCD patients is even more challenging and difficult, since data are scarce regarding stroke occurrence and management in this specific population in the COVID-19 era. This review focuses on pathophysiology of stroke in patients with SCD and possible treatment strategies in the presence of PFO.

Do chronic pain and comorbidities affect brain function in sickle cell patients? A systematic review of neuroimaging and treatment approaches

Sickle cell disease (SCD) is a medical condition in which chronic pain is common and negatively impacts psychosocial function and quality of life. Although the brain mechanisms underlying chronic pain are well studied in other painful conditions, the brain mechanisms underlying chronic pain and the associated psychosocial comorbidities are not well established in SCD. A growing literature demonstrates the effect of treatment of chronic pain, including pharmacological and nonpharmacological treatments, on brain function. The present systematic review aimed to (1) determine the effects of chronic pain and psychosocial comorbidities on brain function of patients with SCD; (2) summarize pharmacological and nonpharmacological approaches to treat these symptoms; and (3) identify areas for further investigation of potential beneficial effects of treatments on brain function. Titles were screened using predefined criteria, including SCD, and abstracts and full texts were reviewed by 2 independent reviewers. A total of 1167 SCD articles were identified, and 86 full articles were included covering 3 sections: chronic pain (4 studies), psychosocial comorbidities (11 studies), and pharmacological and nonpharmacological treatments (71 studies). Neuroimaging evidence demonstrates aberrant neural processing related to chronic pain and psychosocial comorbidities in SCD beyond ischemic stroke and cerebral hemorrhage. Although neuroimaging studies show an important role for psychological factors, pain management is nearly exclusively based on opioids. Behavior therapy seems useful to improve psychological symptoms as well as chronic pain and quality of life. Further investigation is required with larger cohorts, matched controls, and examination of treatment-related neural mechanisms.

Sickle Cell Disease and Stroke: Diagnosis and Management

Both adult and pediatric patients with sickle cell disease face a higher risk of stroke than the general population. Given the different underlying pathophysiology predisposing these patients to stroke, providers should be aware of differences in guidelines for stroke management. This paper reviews diagnostic considerations and recommendations during the evaluation and acute management of patients with sickle cell disease presenting with stroke, focusing on recent updates in the literature. Given the high recurrence rate of stroke in these patients, secondary prevention and curative measures will also be reviewed.

Intelligence quotient in paediatric sickle cell disease: a systematic review and meta-analysis

AIM

Sickle cell disease (SCD) is the commonest cause of childhood stroke worldwide. Magnetic resonance imaging (MRI) is routinely used to detect additional silent cerebral infarction (SCI), as IQ is lower in SCI as well as stroke. This review assesses the effect of infarction on IQ, and specifically whether, compared to healthy controls, IQ differences are seen in children with SCI with no apparent MRI abnormality.

METHOD

A systematic review was conducted to include articles with an SCD paediatric population, MRI information, and Wechsler IQ. A meta-analysis of 19 articles was performed to compare IQ in three groups: stroke vs SCI; SCI vs no SCI; and no SCI vs healthy controls.

RESULTS

Mean differences in IQ between all three groups were significant: stroke patients had lower IQ than patients with SCI by 10 points (six studies); patients with SCI had lower IQ than no patients with SCI by 6 points (17 studies); and no patients with SCI had lower IQ than healthy controls by 7 points (seven studies).

INTERPRETATION

Children with SCD and no apparent MRI abnormality have significantly lower IQ than healthy controls. In this chronic condition, other biological, socioeconomic, and environmental factors must play a significant role in cognition.

Reduced cerebrovascular reserve is regionally associated with cortical thickness reductions in children with sickle cell disease

Sickle cell disease (SCD) is a genetic disorder which adversely affects cerebrovascular health. Previous studies have demonstrated regional cortical thinning in SCD. However, the reason behind regional reductions in cortical thickness remains unclear. Therefore, we aimed to explore the possible link between the state of cerebrovascular health and cortical thickness. In this study, we obtained magnetic resonance (MR) based measures of cerebrovascular reactivity (CVR), a measure of vascular health, and cortical thickness in SCD patients (N=60) and controls of similar age and similar gender ratio (N=27). The group comparison analysis revealed significant regionally specific reductions in CVR and cortical thickness in the SCD group compared to the controls. In addition, a regional association analysis was performed between CVR and cortical thickness in the SCD group which revealed a significant regional association in several brain regions with the highest strength of association observed in the left cuneus, right post central gyrus and the right temporal pole. The regional association analysis revealed that significant associations were found in brain regions with high metabolic activity (anterior cingulate, posterior cingulate, occipital gyrus, precuneus) thus demonstrating that these regions could be most vulnerable to structural damage under hypoxic conditions.

Central nervous system complications and management in sickle cell disease

With advances in brain imaging and completion of randomized clinical trials (RCTs) for primary and secondary stroke prevention, the natural history of central nervous system (CNS) complications in sickle cell disease (SCD) is evolving. In order of current prevalence, the primary CNS complications include silent cerebral infarcts (39% by 18 years), headache (both acute and chronic: 36% in children with sickle cell anemia [SCA]), ischemic stroke (as low as 1% in children with SCA with effective screening and prophylaxis, but ∼11% in children with SCA without screening), and hemorrhagic stroke in children and adults with SCA (3% and 10%, respectively). In high-income countries, RCTs (Stroke Prevention in Sickle Cell Anemia [STOP], STOP II) have demonstrated that regular blood transfusion therapy (typically monthly) achieves primary stroke prevention in children with SCA and high transcranial Doppler (TCD) velocities; after at least a year, hydroxycarbamide may be substituted (TCD With Transfusions Changing to Hydroxyurea [TWiTCH]). Also in high-income countries, RCTs have demonstrated that regular blood transfusion is the optimal current therapy for secondary prevention of infarcts for children with SCA and strokes (Stroke With Transfusions Changing to Hydroxyurea [SWiTCH]) or silent cerebral infarcts (Silent Infarct Transfusion [SIT] Trial). For adults with SCD, CNS complications continue to be a major cause of morbidity and mortality, with no evidence-based strategy for prevention.

Novel insights in the management of sickle cell disease in childhood

Sickle cell disease (SCD) is a life-threatening genetic disorder characterized by chronic hemolytic anemia, vascular injury and multiorgan dysfunctions. Over the last few decades, there have been significant improvements in SCD management in Western countries, especially in pediatric population. An early onset of prophylaxis with Penicillin and a proper treatment of the infections have increased the overall survival in childhood. Nevertheless, management of painful episodes and prevention of organ damage are still challenging and more efforts are needed to better understand the mechanisms behind the development of chronic organ damages. Hydroxyurea (Hydroxycarbamide, HU), the only medication approved as a disease-modifying agent by the United States Food and Drug Administration and the European Medicines Agency, is usually under-used, especially in developing countries. Currently, hematopoietic stem-cell transplantation is considered the only curative option, although its use is limited by lack of donors and transplant-related toxicity. SCD symptoms are similar in children and adults, but complications and systemic organ damages increase with age, leading to early mortality worldwide. Experts in comprehensive care of young patients with SCD, especially those approaching the transition age to adulthood, are missing, leading people to rely on urgent care, increasing health care utilization costs and inappropriate treatments. It would be important to establish programs of comprehensive healthcare for patients with SCD from birth to adulthood, to improve their quality and expectancy of life.

Neuroimaging abnormalities in adults with sickle cell anemia: associations with cognition

OBJECTIVE

This study was conducted to determine the relationship of frontal lobe cortical thickness and basal ganglia volumes to measures of cognition in adults with sickle cell anemia (SCA).

METHODS

Participants included 120 adults with SCA with no history of neurologic dysfunction and 33 healthy controls (HCs). Participants were enrolled at 12 medical center sites, and raters were blinded to diagnostic group. We hypothesized that individuals with SCA would exhibit reductions in frontal lobe cortex thickness and reduced basal ganglia and thalamus volumes compared with HCs and that these structural brain abnormalities would be associated with measures of cognitive functioning (Wechsler Adult Intelligence Scale, 3rd edition).

RESULTS

After adjusting for age, sex, education level, and intracranial volume, participants with SCA exhibited thinner frontal lobe cortex (t = -2.99, p = 0.003) and reduced basal ganglia and thalamus volumes compared with HCs (t = -3.95, p < 0.001). Reduced volume of the basal ganglia and thalamus was significantly associated with lower Performance IQ (model estimate = 3.75, p = 0.004) as well as lower Perceptual Organization (model estimate = 1.44, p = 0.007) and Working Memory scores (model estimate = 1.37, p = 0.015). Frontal lobe cortex thickness was not significantly associated with any cognitive measures.

CONCLUSIONS

Our findings suggest that basal ganglia and thalamus abnormalities may represent a particularly salient contributor to cognitive dysfunction in adults with SCA.

Parent education and biologic factors influence on cognition in sickle cell anemia

Children with sickle cell anemia have a high prevalence of silent cerebral infarcts (SCIs) that are associated with decreased full-scale intelligence quotient (FSIQ). While the educational attainment of parents is a known strong predictor of the cognitive development of children in general, the role of parental education in sickle cell anemia along with other factors that adversely affect cognitive function (anemia, cerebral infarcts) is not known. We tested the hypothesis that both the presence of SCI and parental education would impact FSIQ in children with sickle cell anemia. A multicenter, cross-sectional study was conducted in 19 US sites of the Silent Infarct Transfusion Trial among children with sickle cell anemia, age 5-15 years. All were screened for SCIs. Participants with and without SCI were administered the Wechsler Abbreviated Scale of Intelligence. A total of 150 participants (107 with and 43 without SCIs) were included in the analysis. In a multivariable linear regression model for FSIQ, the absence of college education for the head of household was associated with a decrease of 6.2 points (P = 0.005); presence of SCI with a 5.2 point decrease (P = 0.017); each $1000 of family income per capita with a 0.33 point increase (P = 0.023); each increase of 1 year in age with a 0.96 point decrease (P = 0.023); and each 1% (absolute) decrease in hemoglobin oxygen saturation with 0.75 point decrease (P = 0.030). In conclusion, FSIQ in children with sickle cell anemia is best accounted for by a multivariate model that includes both biologic and socioenvironmental factors.

Silent cerebral infarcts: a review on a prevalent and progressive cause of neurologic injury in sickle cell anemia

Silent cerebral infarct (SCI) is the most common form of neurologic disease in children with sickle cell anemia (SCA). SCI is defined as abnormal magnetic resonance imaging (MRI) of the brain in the setting of a normal neurologic examination without a history or physical findings associated with an overt stroke. SCI occurs in 27% of this population before their sixth, and 37% by their 14th birthdays. In adults with SCA, the clinical history of SCI is poorly defined, although recent evidence suggests that they too may have ongoing risk of progressive injury. Risk factors for SCI include male sex, lower baseline hemoglobin concentration, higher baseline systolic blood pressure, and previous seizures. Specific morbidity associated with SCI includes a decrement in general intellectual abilities, poor academic achievement, progression to overt stroke, and progressive SCI. In addition, children with previous stroke continue to have both overt strokes and new SCI despite receiving regular blood transfusion therapy for secondary stroke prevention. Studies that only include overt stroke as a measure of CNS injury significantly underestimate the total cerebral injury burden in this population. In this review, we describe the epidemiology, natural history, morbidity, medical management, and potential therapeutic options for SCI in SCA.

Event-based prospective memory in children with sickle cell disease: effect of cue distinctiveness

Event-based prospective memory (EB-PM) is the formation of an intention and remembering to perform it in response to a specific event. Currently, EB-PM performance in children with sickle cell disease (SCD) is unknown. In this study, we designed a computer-based task of EB-PM; No-Stroke, Silent-Infarct, and Overt-Stroke groups performed significantly below the demographically similar control group without SCD. Cue distinctiveness was varied to determine if EB-PM could be improved. All groups, with the exception of the Overt-Stroke group, performed significantly better with a perceptually distinctive cue. Overall, these results suggest that EB-PM can be improved significantly in many children with SCD.

Neuropsychological assessment, neuroimaging, and neuropsychiatric evaluation in pediatric and adult patients with sickle cell disease (SCD)

Traditionally, neuropsychological deficits due to Sickle Cell Disease (SCD) have been understudied in adults. We have begun to suspect, however, that symptomatic and asymptomatic Cerebrovascular Events (CVE) may account for an alarming number of deficits in this population. In the current brief review, we critically evaluated the pediatric and adult literatures on the neurocognitive effects of SCD. We highlighted the studies that have been published on this topic and posit that early detection of CVE via neurocognitive testing, neuropsychiatric evaluations, and neuroimaging may significantly reduce adult cognitive and functional morbidities.

Neurocognitive sequelae of pediatric sickle cell disease: a review of the literature

This literature review summarizes all studies relating neuropsychological performance to neuroimaging findings in pediatric sickle cell disease (N=28; published 1991-2005). Although inconsistencies exist within and across domains, deficits in intelligence (IQ), attention and executive functions, memory, language, visuomotor abilities, and academic achievement have been identified. Overall neurocognitive compromise was revealed to be related to the level of neurological injury and the location of silent infarct. Attentional and executive dysfunction is prevalent and related to frontal lobe abnormalities.

Overt and Incomplete (Silent) Cerebral Infarction in Sickle Cell Anemia: Diagnosis and Management

Cerebral vasculopathy in sickle cell anemia (HbSS) is manifest clinically as cerebral infarction and intracranial hemorrhage. The type of stroke, ischemic or hemorrhagic, is age specific with distinct differences in outcomes. Cerebral infarction with or without clinical stroke begins during early childhood and rarely causes death immediately.

Physiological correlates of intellectual function in children with sickle cell disease: hypoxaemia, hyperaemia and brain infarction

Lowered intelligence relative to controls is evident by mid-childhood in children with sickle cell disease. There is consensus that brain infarct contributes to this deficit, but the subtle lowering of IQ in children with normal MRI scans might be accounted for by chronic systemic complications leading to insufficient oxygen delivery to the brain. We investigated the relationship between daytime oxyhaemoglobin saturation (SpO2), cerebral blood flow velocity (CBFV) and intellectual function (IQ) using path-analysis in 30 adolescents with sickle cell disease (mean age 17.4 years, SD 4.2). Initial analyses revealed that the association between SpO2 and Full Scale IQ (FSIQ) was fully mediated by increased CBFV, whereby SpO2 was negatively correlated with CBFV and CBFV was negatively correlated with FSIQ, i.e. decreases in oxygen saturation are associated with increases in velocity, and increased velocity is associated with lowered IQ scores. The mediated relationship suggests that lowered IQ may be a function of abnormal oxygen delivery to the brain. Further analyses showed that the association between CBFV and IQ was significant for verbal but not for performance IQ. The pathophysiology characteristic of SCD can interfere with brain function and constrain intellectual development, even in the absence of an infarct. This supports the hypothesis that lowered intellectual function is partly explained by chronic hypoxia, and has wider implications for our understanding of SCD pathophysiology.

Detecting white matter injury in sickle cell disease using voxel-based morphometry

OBJECTIVE

Sickle cell disease (SCD) is associated with cerebrovascular disease, cerebral infarction, and cognitive dysfunction. This study aimed to detect the presence and extent of white matter abnormalities in individuals with SCD using voxel-based morphometry (VBM).

METHODS

Thirty-six children and adolescents with SCD (age range, 9-24 years) and 31 controls (8-25 years) underwent magnetic resonance investigations using T1- and T2-weighted protocols. White and gray matter density maps were obtained from three-dimensional magnetic resonance imaging (MRI) data sets. Using VBM, we compared the maps between controls and SCD individuals with silent white matter infarct lesions (SCD+L; n = 16), and those without visible abnormality (SCD-L; n = 20).

RESULTS

In comparison with controls, intelligence quotients (IQs) were lower in both SCD groups irrespective of presence of visible lesions. VBM showed widespread bilateral white matter abnormalities in the SCD+L group, extending beyond the regions of focal infarction in the deep anterior and posterior white matter borderzones. Bilateral white matter abnormalities were also observed in the SCD-L group, in locations similar to those in the SCD+L group.

INTERPRETATION

VBM is sensitive to detection of widespread white matter injury in SCD patients in borderzones between arterial territories even in the absence of evidence of infarction. Those changes may contribute to cognitive deficits in this population.

Decreased corpus callosum size in sickle cell disease: relationship with cerebral infarcts and cognitive functioning

We assessed midsagittal corpus callosum size in sickle cell disease (SCD) and its relationship to lesion volume, lesion location, and cognitive functioning. Twenty-eight children with SCD and 16 demographic controls completed magnetic resonance imaging (MRI) and neuropsychological testing. Corpus callosum (CC) size was smaller for children with silent infarcts (n = 8) or overt stroke (n = 8) than for those without visible infarcts (n = 12) or control participants. Lesion volume was a robust predictor of IQ and other cognitive scores; total CC size did not typically add explanatory power for these measures. The size of the rostral body of the CC, however, independently predicted measures of distractibility, speeded production, and working memory. Posterior CC size was also decreased among many of the children with SCD, even in the absence of visible infarcts in this region. Brain morphology appears to provide additional information about SCD-related effects on the brain above and beyond visible infarcts.

Overt and Incomplete (Silent) Cerebral Infarction in Sickle Cell Anemia: Diagnosis and Management

Regional complete infarctions in children with sickle cell anemia (HbSS) are often associated with stenosis of the large intracranial arteries and result in lifetime disability. Incomplete infarction occurs more frequently than previously recognized and has far-reaching effects on neurocognitive development and the risk for overt secondary strokes into adulthood. Clinical and neuroimaging modalities have been highlighted in an algorithmic approach, with the studies giving the highest yield in results and most likely to be available listed in sequential order. The recognition of an emerging "second peak" incidence in the third decade of life is worrisome and warrants more intense scrutiny and diagnosis of subtle findings of stroke in this young adult population.

Defining stroke risk in children with sickle cell anaemia

Sickle cell anaemia (SCA) is the most common cause of childhood stroke, occurring with the highest frequency before the age of 6 years. Despite the relative frequency of stroke in SCA, few predictors of risk exist. Anaemia, leucocytosis, hypertension, silent infarction, and history of acute chest syndrome are well-documented risk factors for ischaemic stroke in SCA. Recent data suggest that other environmental and genetic factors, many unrelated to SCA, influence the development of cerebrovascular disease. Non-invasive assessment of individual stroke risk using transcranial Doppler ultrasonography has provided a means of selecting and prophylactically treating SCA children at highest risk. With the ultimate goal of preventing stroke, the information gained from the studies reviewed here may lead to improved prediction of stroke so that clinical trials to assess risk-based therapy may be carried out on selected children with SCA.

Direct comparison of two methods to measure T1: in vitro and in vivo values by echo-planar imaging and by segmented k-space imaging

We test a hypothesis that proton T(1) is accurately measured independent of the physics inherent to the method. We used two well-validated but quite different imaging methods to measure T(1) in phantoms and in humans; an echo-planar imaging T-one measurement (EPITOME) method, and a segmented k-space acquisition precise and accurate inversion recovery (TurboPAIR) method. Agreement between the methods was generally excellent; the square of the correlation coefficient (r(2)) in phantoms was 0.9996. The r(2) in brain tissue of volunteers was 0.79 overall, and 0.85 if cortical gray matter and corpus callosum were excluded. Nevertheless, small but significant differences were observed between methods in vivo and T(1) measurements were sensitive to tissue type, although measurements could be made comparable. The major difference between the methods is that EPITOME takes 97 s to image 15 slices at low resolution, while TurboPAIR takes 240 s to image one slice at high resolution.

Brain T1 in young children with sickle cell disease: evidence of early abnormalities in brain development

Measurement of tissue spin lattice relaxation time (T(1)) has been used to characterize brain development in healthy children. Here we report the first study of brain T(1) in young children with sickle cell disease (SCD). The T(1) in 10 tissue samples was measured by established techniques; 46 SCD patients under the age of 4 years were compared to 267 controls, including 55 well children under the age of 4 years. A model was developed to predict the relationship between age and brain T(1) in controls, then we compared patient T(1) to healthy normal T(1). Most white matter and gray matter tissues in infant patients (<2 years old), had T(1) values significantly higher than normal. For example, 15.0% of patient caudate T(1) values were above the upper bound of the 95% confidence interval for controls, but only 2.5% of normal values are expected to be this high (p = 0.0003). Among infant patients, brain T(1) was significantly higher than normal in every tissue (p < 0.01) except cortical gray matter. However, patient T(1) values declined rapidly to values lower than normal by about age 4. Our findings imply that patients follow an abnormal developmental trajectory beginning early in infancy.

Transcranial Doppler ultrasonography and neurocognitive functioning in children with sickle cell disease

OBJECTIVE

We examined the relationship between cerebral blood flow velocity, measured by transcranial Doppler (TCD) ultrasonography, and neurocognitive functioning.

METHODS

Participants were 60 children who had sickle cell disease (HbSS) and had no documented history of stroke. Children were classified according to Stroke Prevention Trial in Sickle Cell Anemia criteria (normal, conditional, and abnormal), and their performance was compared on measures of intellectual abilities, academic achievement, sustained attention/concentration, executive function, and parent and teacher ratings of executive function.

RESULTS

Children with abnormal TCD values performed more poorly than children with conditional TCD values on measures of verbal intelligence and executive function. Children with conditional TCD values performed more poorly than children with normal TCD values on measures of sustained attention/concentration and executive function. TCD values also were a significant predictor of auditory working memory in exploratory analyses.

CONCLUSIONS

Our findings support the hypothesis that neurocognitive functions subserved by the frontal systems (eg, sustained attention/concentration and executive function) seem to be the most useful indices of progressive cerebrovasculopathy in children with HbSS disease.

Brain imaging findings in pediatric patients with sickle cell disease

PURPOSE

To determine prevalence of imaging abnormalities in the brain of children with sickle cell disease (SCD) and to identify clinical and methodological factors that influence prevalence estimate.

MATERIALS AND METHODS

Magnetic resonance (MR) imaging and MR angiographic findings for 185 patients with SCD examined at St Jude Children's Research Hospital since 1993 were reviewed. At least two readers independently reviewed images. Standard MR imaging criteria were used to identify lacunae, loss of white matter volume, encephalomalacia, or leukoencephalopathy. Patients were assigned grades to indicate limited or extensive abnormalities. Standard MR angiographic criteria were used to identify arterial tortuosity (limited vasculopathy) and stenosis or occlusion (extensive vasculopathy). Findings were evaluated as a function of patient clinical status (including stroke) and diagnosis. Recent methods (T1- and T2-weighted MR imaging plus fluid-attenuated inversion recovery [FLAIR] at 3-mm section thickness) were compared with older methods (T1- and T2-weighted MR imaging without FLAIR at 5-mm section thickness).

RESULTS

At mean age of 10 years, overall prevalence of infarction, ischemia, or atrophy in patients with SCD was 44% (82 of 185), and prevalence of vasculopathy was 55% (102 of 185), without evidence of a significant referral bias. Twenty-six of 27 patients with clinical stroke had abnormal findings at imaging, but even if patients with stroke were excluded, 35% (56 of 158) had a "silent infarction" (MR imaging-visible injury without clinical stroke), and 49% (78 of 158) had abnormal findings at MR angiography. Patients with clinically severe disease had more abnormalities at MR imaging (P <.001) and MR angiography (P <.004) than did patients with milder disease. Severe vasculopathy was more prevalent in patients with hemoglobin SS than in those with hemoglobin SC (P <.001). Recent imaging methods showed more abnormalities than did older methods (P <.01). With newer methods, 43% (29 of 67) of patients had extensive abnormalities, whereas with older methods, 28% (33 of 116) had extensive abnormalities.

CONCLUSION

Prevalence of ischemic brain injury in pediatric patients with SCD is substantially higher than was previously reported, in part because of improvements in imaging methods.

Sickle cell disease and stroke in a pediatric population

Cerebrovascular complications are common in SCD and constitute a major source of concern to the pediatric hematologist. These complications can be either clinically overt or covert. The authors' review of the diagnostic tests does not offer absolute indications for neuroimaging because most of the evidence is based on studies that are not randomized controlled trials. Imaging guidelines for children have emerged based on the available level 2 and 3 literature, however, CT and MR imaging remain the initial tests of choice for stroke assessment, and TCD is the imaging tool of choice for stroke prevention. Based on guidelines handed down from the NIH, TCD has become a part of routine continuing care of children with SCD.

Age-related changes in the pediatric brain: proton T1 in healthy children and in children with sickle cell disease

The goal of this study was to characterize the expected range of variation in T1 (spin-lattice relaxation time) of brain tissue in vivo, as a function of age, and to use these maturational norms to study children with sickle cell disease (SCD). A well-validated method (TurboPAIR) was used to measure T1 in 10 tissues in a study group of 200 healthy subjects (ages 4.5 to 79.3; 101 male and 99 female), in a transverse slice at the level of the basal ganglia. Brain T1 was significantly related to age in every tissue characterized (p < 0.001), including the splenium (p < 0.01). Quantitative MRI suggests that brain T1 continues to change throughout the lifespan of healthy subjects free of neurologic complaints. Age-related changes follow a different schedule in each tissue, and age is a stronger determinant of T1 in gray matter than in white matter. Analysis of 141 patients with SCD shows that patients have lower T1 than normal, in both the caudate and the cortex (p < 0.001).

Sickle cell and the brain

Sickle cell disease affects many organ systems, but one of the major morbidities is brain disease, especially stroke. In this paper, the etiology, diagnosis, treatment, and prevention of clinical stroke, as well as so-called "silent stroke," are examined. Risk factors, diagnostic tools, and data from prevention and treatment studies as well as issues pertaining to neuropsychological function, especially in younger patients, are discussed and current best options for treatment considered.

Sickle cell disease: the neurological complications

The genetic cause of sickle cell disease has been known for decades, yet the reasons for its clinical variability are not fully understood. The neurological complications result from one point mutation that causes vasculopathy of both large and small vessels. Anemia and the resultant cerebral hyperemia produce conditions of hemodynamic insufficiency. Sickled cells adhere to the endothelium, contributing to a cascade of activated inflammatory cells and clotting factors, which result in a nidus for thrombus formation. Because the cerebrovascular reserve becomes exhausted, the capacity for compensatory cerebral mechanisms is severely limited. There is evidence of small-vessel sludging, and a relative deficiency of nitric oxide in these vessels further reduces compensatory vasodilatation. Both clinical strokes and silent infarcts occur, affecting motor and cognitive function. New data suggest that, in addition to sickle cell disease, other factors, both environmental (eg, hypoxia and inflammation) and genetic (eg, mutations resulting in thrombogenesis), may contribute to a patient's stroke risk. The stroke risk is polygenic, and sickle cell disease can be considered a model for all cerebrovascular disease. This complex disease underscores the potential intellectual and practical distance between the determination of molecular genetics and effective clinical application and therapeutics.

Magnetic resonance imaging in pediatric stroke

Pediatric stroke is a term that can be used to encompass everything from hypoxic-ischemic injury to the fetal central nervous system, and especially the premature neonate, to bland versus hemorrhagic infarction from arterial or venous causes in the infant and older child. Pediatric stroke is a chronically underrecognized and therefore underdiagnosed problem that may have significant economic implications. The risk factors for stroke in children are numerous and differ from those in adults. However, with adequate workup, the etiology can be identified in about 75% of cases. Cardiac disorders and hemoglobinopathy are the most common causes of ischemic infarction in children, whereas various congenital anomalies of the blood vessels or defects in coagulation or platelet function often are found in children with parenchymal hemorrhage. Magnetic resonance imaging provides a noninvasive method of investigating childhood stroke, aiding in both better diagnosis and management of this problem.

Neuropsychological aspects of pediatric sickle cell disease

Sickle cell disease (SCD), a class of genetic disorders characterized by abnormal, sickled red blood cells, is a chronic illness that results in progressive cerebrovascular disease. Neurocognitive sequelae of clinically apparent cerebrovascular accidents in children with SCD are characterized by pervasive impairments, including decrements in general intellectual functioning, language and verbal abilities, visual-motor and visual-spatial processing, memory, academic achievement, and processing of subtle prosodic information. In contrast, subtle neurocognitive deficits in the areas of attention and concentration, executive function, and visual-motor speed and coordination appear to be associated with silent infarcts that are not necessarily detected on physical examination. Investigation of the disease course and associated neurocognitive sequelae suggest a disease-specific model of neuropsychological impairment. Recommendations are made for clinical and research efforts in the field of pediatric neuropsychology.

Effect of therapeutic ionizing radiation on the human brain

We test a hypothesis that fractionated radiation therapy within a therapeutic dose range is associated with a dose-related change in normal brain, detectable by quantitative magnetic resonance imaging. A total of 33 patients were examined by quantitative magnetic resonance imaging to measure brain tissue spin-lattice relaxation time (T1) before treatment, and at various times during and after radiation therapy. A T1 map was generated at each time point, and radiation therapy isodose contours were superimposed on the corresponding segmented T1 map. Changes in white matter and gray matter T1 were analyzed as a function of radiation therapy dose and time since treatment, controlling for patient age and tumor site. In white matter, a dose level of more than 20 Gy was associated with a dose-dependent decrease in T1 over time, which became significant 6 months after treatment. There was no significant change in T1 of gray matter over time, at radiation therapy doses of less than 60 Gy. However, GM in close proximity to the tumor had a lower T1 before therapy. Our results represent the first radiation dose-response data derived from pediatric brain in vivo. These findings confirm that white matter is more vulnerable to radiation-induced change than is gray matter, and suggest that T1 mapping is sensitive to radiation-related changes over a broad dose range (20 to 60 Gy). Human white matter T1 is not sensitive to radiation therapy of less than 20 Gy, and gray matter T1 is unchanged over the dose range used to treat human brain tumor. The reduction of gray matter T1 near the tumor could result from compression of cortical parenchyma near the growing tumor mass, or from tumor cell invasion directly into the parenchyma. If brain T1 is a surrogate for radiation effect, reducing the volume of normal white matter receiving more than 20 Gy could be an important treatment planning goal.

Sickle cell anemia

Sickle cell anemia (SCA) is a disease caused by production of abnormal hemoglobin, which binds with other abnormal hemoglobin molecules within the red blood cell to cause rigid deformation of the cell. This deformation impairs the ability of the cell to pass through small vascular channels; sludging and congestion of vascular beds may result, followed by tissue ischemia and infarction. Infarction is common throughout the body in the patient with SCA, and it is responsible for the earliest clinical manifestation, the acute pain crisis, which is thought to result from marrow infarction. Over time, such insults result in medullary bone infarcts and epiphyseal osteonecrosis. In the brain, white matter and gray matter infarcts are seen, causing cognitive impairment and functional neurologic deficits. The lungs are also commonly affected, with infarcts, emboli (from marrow infarcts and fat necrosis), and a markedly increased propensity for pneumonia. The liver, spleen, and kidney may experience infarction as well. An unusual but life-threatening complication of SCA is sequestration syndrome, wherein a considerable amount of the intravascular volume is sequestered in an organ (usually the spleen), causing vascular collapse; its pathogenesis is unknown. Finally, because the red blood cells are abnormal, they are removed from the circulation, resulting in a hemolytic anemia. For the patient with SCA, however, the ischemic complications of the disease far outweigh the anemia in clinical importance.

Effect of increased repetition time TR on precision of inversion-recovery T 1 measurements

The effect of increased repetition time, TR, on the precision of inversion-recovery measurements of the spin-lattice relaxation time, T(1), was calculated theoretically, simulated numerically, and measured experimentally. All three methods yielded similar results. With constant inversion times, the T(1) precision was independent of TR. Therefore, 1) multiple-slice inversion-recovery fast-spin-echo T(1) maps should be made one slice at a time, not with interleaved acquisition, and 2) once the longest inversion time t(i) has been set, TR should be set just enough longer than the longest t(i) to allow data acquisition.

Effect of ionizing radiation on the human brain: white matter and gray matter T1 in pediatric brain tumor patients treated with conformal radiation therapy

OBJECTIVE

To test a hypothesis that fractionated radiation therapy (RT) to less than 60 Gy is associated with a dose-related change in the spin-lattice relaxation time (T1) of normal brain tissue, and that such changes are detectable by quantitative MRI (qMRI).

METHODS

Each of 21 patients received a qMRI examination before treatment, and at several time points during and after RT. A map of brain T1 was calculated and segmented into white matter and gray matter at each time point. The RT isodose contours were then superimposed upon the T1 map, and changes in brain tissue T1 were analyzed as a function of radiation dose and time following treatment. We used a mixed-model analysis to analyze the longitudinal trend in brain T1 from the start of RT to 1 year later. Predictive factors evaluated included patient age and clinical variables, such as RT dose, time since treatment, and the use of an imaging contrast agent.

RESULTS

In white matter (WM), a dose level of greater than 20 Gy was associated with a dose-dependent decrease in T1 over time, which became significant about 3 months following treatment. In gray matter (GM), there was no significant change in T1 over time, as a function of RT doses < 60 Gy. However, GM in close proximity to the tumor had an inherently lower T1 before therapy. Neither use of a contrast agent nor a combination of chemotherapy plus steroids had a significant effect on brain T1.

CONCLUSION

Results suggest that T1 mapping may be sensitive to radiation-related changes in human brain tissue T1. WM T1 appears to be unaffected by RT at doses less than approximately 20 Gy; GM T1 does not change at doses less than 60 Gy. However, tumor appears to have an effect upon adjacent GM, even before treatment. Conformal RT may offer a substantial benefit to the patient, by minimizing the volume of normal brain exposed to greater than 20 Gy.

More than meets the eye: significant regional heterogeneity in human cortical T1

Segmented k-space acquisition of data was used to decrease the acquisition time and to increase the imaging resolution of the precise and accurate inversion recovery (PAIR) method of measuring T(1). We validated the new TurboPAIR method by measuring T(1) in 158 regions of interest in 12 volunteers, using both PAIR and TurboPAIR. We found a 3% difference between methods, which could be corrected by linear regression. After validation, the TurboPAIR method was used to test a hypothesis that there is significant regional heterogeneity in cortical T(1). We measured cortical gray matter T(1) in 11 right-handed volunteers, in 48 regions of interest scattered over frontal and parietal cortex, and in 46 ROIs along the central sulcus (CS). We found that T(1) in the CS is less than T(1) elsewhere in the cortex (p<0.001), and that there is considerable hemispheric asymmetry in T(1) in gray matter, but not in white matter. In central gray structures (caudate, thalamus, nucleus pulvinarus), and in the posterior CS (sensory cortex), right hemisphere T(1) was significantly greater than left hemisphere T(1) (p< or =0.004). In cortical gray matter of the frontal lobe and anterior CS (motor cortex), left hemisphere T(1) was significantly greater than right hemisphere T(1) (p< or =0.003). These findings demonstrate that there is considerable regional heterogeneity in human cortical T(1) that is unexplained by differences in tissue iron content, but may be evidence of an inherent anatomic asymmetry of the brain.

Diffuse T1 reduction in gray matter of sickle cell disease patients: evidence of selective vulnerability to damage?

The objective of our study was to test the hypothesis that subtle brain abnormality can be present in pediatric sickle cell disease (SCD) patients normal by conventional MR imaging (cMRI). We examined 50 SCD patients to identify those patients who were normal by cMRI. Quantitative MR imaging (qMRI) was then used to map spin-lattice relaxation time (T1) in a single slice in brain tissue of all 50 patients and in 52 healthy age-similar controls. We also used a radiofrequency (RF) pulse to saturate blood spins flowing into the T1 map slice, to characterize the effect of blood flow on brain T1. Abnormalities were noted by cMRI in 42% (21/50) of patients, with lacunae in 32%, and encephalo malacia in 20%. Brain T1 in patients normal by cMRI was significantly lower than controls, in caudate, thalamus, and cortex (p < or =0.007), and regression showed that gray matter T1 abnormality was present in caudate and cortex by age 4 (p < or =0.002). In patients abnormal by cMRI, T1 reductions in gray matter were larger and more significant. White matter T1 was not significantly increased except in patients abnormal by cMRI. RF saturation in a slab below the T1 map produced no significant change in T1, compared to RF saturation in a slab above the T1 map, suggesting that inflow of untipped spins in blood does not cause an artifactual shortening of T1. Gray matter T1 abnormality was present in patients normal by cMRI, while white matter T1 abnormality was present only in patients also abnormal by cMRI. These findings suggest that gray matter is selectively vulnerable to damage in pediatric SCD patients and that white matter damage occurs later in the disease process. Our inability to find an effect from saturation of inflowing blood implies that rapid perfusion cannot account for T1 reduction in gray matter.

Subtle brain abnormalities in children with sickle cell disease: relationship to blood hematocrit

Our objective was to test a hypothesis that subtle brain abnormality can be present in pediatric sickle cell disease (SCD) patients who are clinically free of stroke. We prospectively compared 50 patients with 52 healthy age-similar controls, using quantitative magnetic resonance imaging. A previously validated precise and accurate inversion-recovery method was used to measure T1 in a slice at the basal ganglia. We also used the Wechsler test to measure intelligence quotient (IQ) in a randomly selected subset of 27 patients. Brain T1 was significantly lower in patients in every gray matter structure evaluated but in none of the white matter structures. Regression suggests that T1 in caudate, nucleus pulvinares, and cerebral cortex was abnormal by age 4 years. Psychometric testing showed that 33% of patients were functioning in the range of mild mental deficiency (IQ, 50-70), compared with a published prevalence of 1.45% in inner-city black children. Thus, in our patients, SCD was associated with a 23-fold increase in the risk of mild mental deficiency. Full-scale IQ of SCD patients was a function of hematocrit (Hct), and when Hct was used to stratify patients, those with an Hct of less than 27% had significantly lower psychometric test scores, and significantly lower gray matter T1, than those with an Hct of 27 or more. Both cognitive deficits and subtle T1 abnormalities were associated with a low Hct, and both could be present when conventional magnetic resonance imaging findings were normal. Our findings suggest that chronic hypoxia of brain tissue can occur in SCD patients free of clinical stroke.

Effect of a gadodiamide contrast agent on the reliability of brain tissue T1 measurements

To determine whether brain spin-lattice relaxation time (T1) can routinely be measured after contrast-agent injection, we measured T1 by a precise and accurate inversion-recovery (PAIR) method in five brain tumor patients, before and again after contrast-agent injection. The T1 in at least 20 regions of interest (ROIs) was measured in each patient, avoiding areas of contrast enhancement visible by conventional MR imaging. Contrast-agent injection reduced T1 in 51 regions of interest in white matter by less than 1% (not significant), and in 50 regions of interest in gray matter by less than 2% (p = 0.001). Pixel-by-pixel plots demonstrate that T1 is reduced substantially in extra-parenchymal tissues, but not in brain tissues. Therefore, T1 mapping with the precise and accurate inversion-recovery method can routinely be done after contrast injection. Our results suggest that the precise and accurate inversion-recovery method is not sensitive to the T1 of blood in the presence of an intact blood-brain barrier, although a substantial T1 reduction does occur in the absence of a blood-brain barrier.

Correction of errors caused by imperfect inversion pulses in MR imaging measurement of T1 relaxation times

Spin-lattice (T1) relaxation times were measured by an inversion-recovery magnetic resonance imaging method with a slice-selective inversion pulse (SIP), a non-selective rectangular inversion pulse (RIP), or a B1-insensitive adiabatic inversion pulse (AIP). Data analysis either assumed perfect inversion (two-parameter fit) or allowed for imperfect inversion (three-parameter fit). Imperfect inversion pulses caused low T1 values in phantoms with a two-parameter fit, while three-parameter T1 estimates were accurate over the range 430-2670 ms. A difference of approximately 10% between two-parameter and three-parameter T1 values in normal human brain tissue was attributed to B1 inhomogeneity with the slice-selective inversion pulse and rectangular inversion pulse, to the slice profile with the slice-selective inversion pulse, and to T2 effects for the adiabatic inversion pulse. Any T1 method that relies on accurate flip angles may have a significant systematic error in vivo. Phantom accuracy does not ensure accuracy in vivo, because phantoms may have a more homogeneous B1 field and a longer T2 than do biological samples.