Longitudinal comparison of pre- and postoperative diffusion tensor imaging parameters in young children with hydrocephalus

Structural and functional connectivity in hydrocephalus: a scoping review

Optimizing the treatment of hydrocephalus remains a major challenge in adult and pediatric neurosurgery. Currently, clinical treatment relies heavily on anatomic imaging of ventricular size and clinical presentation. The emergence of functional and structural brain connectivity imaging has provided the basis for a new paradigm in the management of hydrocephalus. Here we review the pertinent advances in this field. Following PRISMA-ScR guidelines for scoping reviews, we searched PubMed for relevant literature from 1994 to April 2023 using hydrocephalus and MRI-related terms. Included articles reported original MRI data on human subjects with hydrocephalus, while excluding non-English or pre-1994 publications that didn't match the study framework. The review identified 44 studies that investigated functional and/or structural connectivity using various MRI techniques across different hydrocephalus populations. While there is significant heterogeneity in imaging technology and connectivity analysis, there is broad consensus in the literature that 1) hydrocephalus is associated with disruption of functional and structural connectivity, 2) this disruption in cerebral connectivity can be further associated with neurologic compromise 3) timely treatment of hydrocephalus restores both cerebral connectivity and neurologic compromise. The robustness and consistency of these findings vary as a function of patient age, hydrocephalus etiology, and the connectivity region of interest studied. Functional and structural brain connectivity imaging shows potential as an imaging biomarker that may facilitate optimization of hydrocephalus treatment. Future research should focus on standardizing regions of interest as well as identifying connectivity analysis most pertinent to clinical outcome.

Structural Alterations of the Corpus Callosum in Children With Infantile Hydrocephalus

This study investigates structural alterations of the corpus callosum in children diagnosed with infantile hydrocephalus. We aim to assess both macrostructural (volume) and microstructural (diffusion tensor imaging metrics) facets of the corpus callosum, providing insights into the nature and extent of alterations associated with this condition. Eighteen patients with infantile hydrocephalus (mean age = 9 years) and 18 age- and sex-matched typically developing healthy children participated in the study. Structural magnetic resonance imaging and diffusion tensor imaging were used to assess corpus callosum volume and microstructure, respectively. Our findings reveal significant alterations in corpus callosum volume, particularly in the posterior area, as well as distinct microstructural disparities, notably pronounced in these same segments. These results highlight the intricate interplay between macrostructural and microstructural aspects in understanding the impact of infantile hydrocephalus. Examining these structural alterations provides an understanding into the mechanisms underlying the effects of infantile hydrocephalus on corpus callosum integrity, given its pivotal role in interhemispheric communication. This knowledge offers a more nuanced perspective on neurologic disorders and underscores the significance of investigating the corpus callosum's health in such contexts.

Structural networking of the developing brain: from maturation to neurosurgical implications

Modern neuroscience agrees that neurological processing emerges from the multimodal interaction among multiple cortical and subcortical neuronal hubs, connected at short and long distance by white matter, to form a largely integrated and dynamic network, called the brain "connectome." The final architecture of these circuits results from a complex, continuous, and highly protracted development process of several axonal pathways that constitute the anatomical substrate of neuronal interactions. Awareness of the network organization of the central nervous system is crucial not only to understand the basis of children's neurological development, but also it may be of special interest to improve the quality of neurosurgical treatments of many pediatric diseases. Although there are a flourishing number of neuroimaging studies of the connectome, a comprehensive vision linking this research to neurosurgical practice is still lacking in the current pediatric literature. The goal of this review is to contribute to bridging this gap. In the first part, we summarize the main current knowledge concerning brain network maturation and its involvement in different aspects of normal neurocognitive development as well as in the pathophysiology of specific diseases. The final section is devoted to identifying possible implications of this knowledge in the neurosurgical field, especially in epilepsy and tumor surgery, and to discuss promising perspectives for future investigations.

Tumor region associated with specific processing speed outcomes

OBJECTIVE

Processing speed (PS) is a vulnerable cognitive skill in pediatric cancer survivors as a consequence of treatments and, less consistently, tumor region. Studies conventionally examine graphomotor PS; emerging research suggests other aspects of PS may be impacted. This study examined types of PS in pediatric brain tumor survivors to determine which aspects are impaired. Given discordance across studies, we additionally investigated the relationship between brain region and PS.

METHODS

The sample consisted of 167 pediatric brain tumor patients (100 supratentorial). PS (oral naming, semantic fluency, phonemic fluency, motor speed, graphomotor speed, visual scanning) was gathered via clinical neuropsychological assessment. To examine PS by region, infratentorial and supratentorial groups were matched on age at diagnosis and neuropsychological assessment, and time since diagnosis.

RESULTS

The whole sample performed below normative means on measures of oral naming (p < .001), phonemic fluency (p < .001), motor speed (p = .03), visual scanning (p < .001), and graphomotor speed (p < .001). Only oral naming differed by region (p = .03), with infratentorial tumors associated with slower performance. After controlling for known medical and demographic risk factors, brain region remained a significant predictor of performance (p = .04). Among the whole sample, greater than expected proportions of patients with impairment (i.e., >1 standard deviation below the normative mean) were seen across all PS measures. Infratentorial tumors had higher rates of impairments across all PS measures except phonemic fluency.

CONCLUSIONS

Results indicate pediatric brain tumor survivors demonstrate weaknesses in multiple aspects of PS, suggesting impairments are not secondary to peripheral motor slowing alone. Additionally, tumor region may predict some but not all neuropsychological outcomes in this population.

Brain Network Connectivity and Executive Function in Children with Previous Infantile Hydrocephalus

INTRODUCTION

Infantile hydrocephalus is a condition in which there is an abnormal build-up of cerebrospinal fluid in the ventricles within the first few months of life, which puts pressure on surrounding brain tissues. Compression of the developing brain increases the risk of secondary brain injury and cognitive disabilities.

METHODS

In this study, we used diffusion-weighted imaging and resting-state functional MRI to investigate the effects of ventricle dilatation on structural and functional brain networks in children with shunted infantile hydrocephalus and examined how these brain changes may impact executive function.

RESULTS

We found that children with hydrocephalus have altered structural and functional connectivity between and within large-scale networks. Moreover, hyperconnectivity between the ventral attention and default mode network in children with hydrocephalus correlated with reduced executive function scores. Compared to typically developing age-matched control participants, our patient population also had lower fractional anisotropy in posterior white matter.

DISCUSSION

Overall, these findings suggest that infantile hydrocephalus has long-term effects on brain network connectivity, white matter development, and executive function in children at school-age. Future work will examine the relationship between ventricular volumes prior to shunt placement in infancy and brain network development throughout childhood.

Diffusion tensor magnetic resonance imaging of the optic nerves in pediatric hydrocephalus

OBJECTIVE

While conventional imaging can readily identify ventricular enlargement in hydrocephalus, structural changes that underlie microscopic tissue injury might be more difficult to capture. MRI-based diffusion tensor imaging (DTI) uses properties of water motion to uncover changes in the tissue microenvironment. The authors hypothesized that DTI can identify alterations in optic nerve microstructure in children with hydrocephalus.

METHODS

The authors retrospectively reviewed 21 children (< 18 years old) who underwent DTI before and after neurosurgical intervention for acute obstructive hydrocephalus from posterior fossa tumors. Their optic nerve quantitative DTI metrics of mean diffusivity (MD) and fractional anisotropy (FA) were compared to those of 21 age-matched healthy controls.

RESULTS

Patients with hydrocephalus had increased MD and decreased FA in bilateral optic nerves, compared to controls (p < 0.001). Normalization of bilateral optic nerve MD and FA on short-term follow-up (median 1 day) after neurosurgical intervention was observed, as was near-complete recovery of MD on long-term follow-up (median 1.8 years).

CONCLUSIONS

DTI was used to demonstrate reversible alterations of optic nerve microstructure in children presenting acutely with obstructive hydrocephalus. Alterations in optic nerve MD and FA returned to near-normal levels on short- and long-term follow-up, suggesting that surgical intervention can restore optic nerve tissue microstructure. This technique is a safe, noninvasive imaging tool that quantifies alterations of neural tissue, with a potential role for evaluation of pediatric hydrocephalus.

Abnormal anisotropic diffusion properties in pediatric myelomeningocele patients treated with fetal surgery: an initial DTI study

PURPOSE

To investigate white matter microstructural abnormality based on diffusion tensor imaging (DTI) in pediatric patients with fetal repair for myelomeningocele (MMC).

METHODS

This was a retrospective analysis of DTI data from 8 pediatric patients with prenatal MMC repair (age range 1.64-33.70 months; sex 3F/5M) and 8 age-matched controls (age 2.24-31.20 months; sex 5F/2M). All participants were scanned on 1.5T GE Signa MR scanner (GE Healthcare, Milwaukee, WI) with the same sequence specifications. Two DTI measures, including fractional anisotropy (FA) and mean diffusivity (MD), were calculated from the genu of corpus callosum (gCC) and the posterior limb of internal capsule (PLIC). DTI values and fronto-occipital horn ratio (FOHR) were tested for group difference based on two-tailed paired t test.

RESULTS

The ventricle size based on FOHR in patients with prenatal MMC repair was significantly larger than that in the age-matched control group (p < 0.001). Statistically significant group difference in DTI (lower FA and higher MD in patient group) was found in gCC (p = 0.007 and 0.003, respectively). A trend level increase in MD was also found (p = 0.065) in PLIC in patients when compared with the age-matched controls.

CONCLUSION

Our data showed white matter abnormality based on DTI in pediatric patient with fetal repair for MMC. The sensitivity of DTI in detecting white matter abnormality, as shown in the present study, may help to serve as an imaging biomarker for assessing hydrocephalus and improve and optimize decision making for the treatment of hydrocephalus in this patient population.

Long-Term Intellectual and Fine Motor Outcomes in Spina Bifida Are Related to Myelomeningocele Repair and Shunt Intervention History

OBJECTIVE

Lifespan outcomes of simultaneous versus sequential myelomeningocele repair and shunt placement or effects of repeated shunt revisions on specific domains of IQ or fine motor dexterity are largely unknown. The current study addressed these gaps in a large cohort of children and adults with spina bifida myelomeningocele (SBM).

METHODS

Participants between 7 and 44 years of age with SBM and shunted hydrocephalus were recruited from international clinics at two time points. Each participant completed a standardized neuropsychological evaluation that included estimates of IQ and fine motor dexterity. Simultaneous versus sequential surgical repair and number of shunt revisions were examined in relation to long-term IQ and fine motor scores.

RESULTS

Simultaneous myelomeningocele repair and shunting were associated with more frequent shunt revisions, as well as to lower Full Scale and verbal IQ scores, controlling for number of shunt revisions. More shunt revisions across study time points were associated with higher nonverbal IQ (NVIQ) scores. No effects were observed on fine motor dexterity.

CONCLUSIONS

Findings indicate generally greater influence of surgery type over shunt revision history on outcomes in well-managed hydrocephalus. Findings supported apparent, domain-specific benefits of sequential compared to simultaneous surgery across the lifespan in SBM. Higher NVIQ scores with greater number of additional shunt revisions across surgery type supported positive outcomes with effective surgical management for hydrocephalus.

Detection of differentiated changes in gray matter in children with progressive hydrocephalus and chronic compensated hydrocephalus using voxel-based morphometry and machine learning

Currently, no neuroimaging study has reported the detection of specific imaging biomarkers that distinguish the progressive hydrocephalus (PH) and chronic compensated hydrocephalus (CH). Our main focus is to evaluate the different structural changes in classifying the two types of hydrocephalus children. Twenty-two children with hydrocephalus (12 PHs and 10 CHs) and 30 age-matched healthy controls were enrolled and the T1-weighted imaging was collected in the study. A customized voxel-based morphometry (VBM) approach and support vector machine (SVM) were combined to investigate the structural changes and group classification. Comparing with the controls and CH, PH groups invariably showed a significant decrease of GM volume in the bilateral hippocampus/parahippocampus, insula, and motor-related areas. SVM applied to the GM volumes of bilateral hippocampus/parahippocampus, insula, and motor-related areas correctly identified hydrocephalus children from normal controls with a statistically significant accuracy of 88.46% (p ≤ .001). In addition, SVM applied to GM volumes of the same regions correctly identified PH from CH with a statistically significant accuracy of 77.27% (p ≤ .009). Using VBM analysis, we characterized and visualized the GM changes in children with hydrocephalus. Machine learning results further confirmed that a significant decrease of the bilateral hippocampus/parahippocampus, insula, and motor-related GM volume can serve as a specific neuroimaging index to distinguish the children with PH from the children with CH and controls at individual. The findings could help to aid the identification of individuals with PH in clinical practice.

Diffusion tensor imaging and ventricle volume quantification in patients with chronic shunt-treated hydrocephalus: a matched case-control study

OBJECTIVEThe object of this study was to use diffusion tensor imaging (DTI) and tract-based spatial statistics (TBSS) to characterize the long-term effects of hydrocephalus and shunting on white matter integrity and to investigate the relationship of ventricular size and alterations in white matter integrity with headache and quality-of-life outcome measures.METHODSPatients with shunt-treated hydrocephalus and age- and sex-matched healthy controls were recruited into the study and underwent anatomical and DTI imaging on a 3-T MRI scanner. All patients were clinically stable, had undergone CSF shunt placement before 2 years of age, and had a documented history of complaints of headaches. Outcome was scored based on the Headache Disability Inventory and the Hydrocephalus Outcome Questionnaire. Fractional anisotropy (FA) and other DTI-based measures (axial, radial, and mean diffusivity; AD, RD, and MD, respectively) were extracted in the corpus callosum and internal capsule with manual region-of-interest delineation and in other regions with TBSS. Paired t-tests, corrected with a 5% false discovery rate, were used to identify regions with significant differences between patients and controls. Within the patient group, linear regression models were used to investigate the relationship between FA or ventricular volume and outcome, as well as the effect of shunt-related covariates.RESULTSTwenty-one hydrocephalus patients and 21 matched controls completed the study, and their data were used in the final analysis. The authors found significantly lower FA for patients than for controls in 20 of the 48 regions, mostly posterior white matter structures, in periventricular as well as more distal tracts. Of these 20 regions, 17 demonstrated increased RD, while only 5 showed increased MD and 3 showed decreased AD. No areas of increased FA were observed. Higher FA in specific periventricular white matter tracts, tending toward FA in controls, was associated with increased ventricular size, as well as improved clinical outcome.CONCLUSIONSThe study shows that TBSS-based DTI is a sensitive technique for elucidating changes in white matter structures due to hydrocephalus and chronic CSF shunting and provides preliminary evidence that DTI may be a valuable tool for tailoring shunt procedures to monitor ventricular size following shunting and achieve optimal outcome, as well as for guiding the development of alternate therapies for hydrocephalus.

Feasibility of fast brain diffusion MRI to quantify white matter injury in pediatric hydrocephalus

OBJECTIVE

Traditionally, diffusion MRI (dMRI) has been performed in parallel with high-resolution conventional MRI, which requires long scan times and may require sedation or general anesthesia in infants and young children. Conversely, fast brain MRI permits image acquisition without the need for sedation, although its short pulse sequences, susceptibility to motion artifact, and contrast resolution have limited its use to assessing ventricular size or major structural variations. Here, the authors demonstrate the feasibility of leveraging a 3-direction fast brain MRI protocol to obtain reliable dMRI measures.

METHODS

Fast brain MRI with 3-direction dMRI was performed in infants and children before and after hydrocephalus treatment. Regions of interest in the posterior limbs of the internal capsules (PLICs) and the genu of the corpus callosum (gCC) were drawn on diffusion-weighted images, and mean diffusivity (MD) data were extracted. Ventricular size was determined by the frontal occipital horn ratio (FOHR). Differences between and within groups pre- and posttreatment, and FOHR-MD correlations were assessed.

RESULTS

Of 40 patients who met inclusion criteria (median age 27.5 months), 15 (37.5%), 17 (42.5%), and 8 (20.0%) had posthemorrhagic hydrocephalus (PHH), congenital hydrocephalus (CH), or no intracranial abnormality (controls), respectively. A hydrocephalus group included both PHH and CH patients. Prior to treatment, the FOHR (p < 0.001) and PLIC MD (p = 0.027) were greater in the hydrocephalus group than in the controls. While the mean gCC MD in the hydrocephalus group (1.10 × 10-3 mm2/sec) was higher than that of the control group (0.98), the difference was not significant (p = 0.135). Following a median follow-up duration of 14 months, decreases in FOHR, PLIC MD, and gCC MD were observed in the hydrocephalus group and were similar to those in the control group (p = 0.107, p = 0.702, and p = 0.169, respectively). There were no correlations identified between FOHR and MDs at either time point.

CONCLUSIONS

The utility of fast brain MRI can be extended beyond anatomical assessments to obtain dMRI measures. A reduction in PLIC and gCC MD to levels similar to those of controls was observed within 14 months following shunt surgery for hydrocephalus in PHH and CH infants. Further studies are required to assess the role of fast brain dMRI for assessing clinical outcomes in pediatric hydrocephalus patients.

Preterm neuroimaging and neurodevelopmental outcome: a focus on intraventricular hemorrhage, post-hemorrhagic hydrocephalus, and associated brain injury

Intraventricular hemorrhage in the setting of prematurity remains the most common cause of acquired hydrocephalus. Neonates with progressive post-hemorrhagic hydrocephalus are at risk for adverse neurodevelopmental outcomes. The goal of this review is to describe the distinct and often overlapping types of brain injury in the preterm neonate, with a focus on neonatal hydrocephalus, and to connect injury on imaging to neurodevelopmental outcome risk. Head ultrasound and magnetic resonance imaging findings are described separately. The current state of the literature is imprecise and we end the review with recommendations for future radiologic and neurodevelopmental research.

Effects of Melatonin on the Cerebellum of Infant Rat Following Kaolin-Induced Hydrocephalus: a Histochemical and Immunohistochemical Study

Hydrocephalus is a developmental disorder causing abnormally collected cerebrospinal fluid within the cerebral ventricles. It leads to bigger skulls and many dysfunctions related to the nervous system. Here, we addressed whether exogenous melatonin administration could reverse the clinical features of kaolin-induced hydrocephalus in infantile rats. A controlled double-blinded study was conducted in 2-week-old 45 Wistar albino rats, which were divided into three groups: Group A, the control group, received intracisternal sham injection with solely the needle insertion; group B, the hydrocephalus group, was treated with isotonic NaCl after kaolin injection; and group C, the hydrocephalus + melatonin group, was given i.p. exogenous melatonin at a dose of 0.5 mg/100 g body weight after kaolin injection. Histological and immunohistochemical analyses were performed after the induction of hydrocephalus and melatonin administration. Glial fibrillary acidic protein was stained by immunohistochemical method. TUNEL method was used to define and quantitate apoptosis in the cerebellar tissues. Statistical analysis was performed by nonparametric Kruskal-Wallis H test, and once significance was determined among means, post hoc pairwise comparisons were carried out using Mann-Whitney U test. We found that melatonin administration significantly ameliorated ratio of substantia grisea area/substantia alba area in the cerebellum of infantile rats. Histologically, there was a significant reduction in the number of cerebellar apoptotic cells after the hydrocephalus induced by kaolin (P < 0.05). Our results clearly revealed that the histopathological changes in the cerebellum were reversed by systemic melatonin administration in infantile rats with kaolin-induced hydrocephalus. Nevertheless, further studies are needed to suggest melatonin as a candidate protective drug in children with hydrocephalus.

Are Shunt Revisions Associated with IQ in Congenital Hydrocephalus? A Meta -Analysis

Although it is generally acknowledged that shunt revisions are associated with reductions in cognitive functions in individuals with congenital hydrocephalus, the literature yields mixed results and is inconclusive. The current study used meta-analytic methods to empirically synthesize studies addressing the association of shunt revisions and IQ in individuals with congenital hydrocephalus. Six studies and three in-house datasets yielded 11 independent samples for meta-analysis. Groups representing lower and higher numbers of shunt revisions were coded to generate effect sizes for differences in IQ scores. Mean effect size across studies was statistically significant, but small (Hedges' g = 0.25, p < 0.001, 95 % CI [0.08, 0.43]) with more shunt revisions associated with lower IQ scores. Results show an association of lower IQ and more shunt revisions of about 3 IQ points, a small effect, but within the error of measurement associated with IQ tests. Although clinical significance of this effect is not clear, results suggest that repeated shunt revisions because of shunt failure is associated with a reduction in cognitive functions.

Left hemisphere structural connectivity abnormality in pediatric hydrocephalus patients following surgery

Neuroimaging research in surgically treated pediatric hydrocephalus patients remains challenging due to the artifact caused by programmable shunt. Our previous study has demonstrated significant alterations in the whole brain white matter structural connectivity based on diffusion tensor imaging (DTI) and graph theoretical analysis in children with hydrocephalus prior to surgery or in surgically treated children without programmable shunts. This study seeks to investigate the impact of brain injury on the topological features in the left hemisphere, contratelateral to the shunt placement, which will avoid the influence of shunt artifacts and makes further group comparisons feasible for children with programmable shunt valves. Three groups of children (34 in the control group, 12 in the 3-month post-surgery group, and 24 in the 12-month post-surgery group, age between 1 and 18 years) were included in the study. The structural connectivity data processing and analysis were performed based on DTI and graph theoretical analysis. Specific procedures were revised to include only left brain imaging data in normalization, parcellation, and fiber counting from DTI tractography. Our results showed that, when compared to controls, children with hydrocephalus in both the 3-month and 12-month post-surgery groups had significantly lower normalized clustering coefficient, lower small-worldness, and higher global efficiency (all p < 0.05, corrected). At a regional level, both patient groups showed significant alteration in one or more regional connectivity measures in a series of brain regions in the left hemisphere (8 and 10 regions in the 3-month post-surgery and the 12-month post-surgery group, respectively, all p < 0.05, corrected). No significant correlation was found between any of the global or regional measures and the contemporaneous neuropsychological outcomes [the General Adaptive Composite (GAC) from the Adaptive Behavior Assessment System, Second Edition (ABAS-II)]. However, one global network measure (global efficiency) and two regional network measures in the insula (local efficiency and between centrality) tested at 3-month post-surgery were found to correlate with GAC score tested at 12-month post-surgery with statistical significance (all p < 0.05, corrected). Our data showed that the structural connectivity analysis based on DTI and graph theory was sensitive in detecting both global and regional network abnormality when the analysis was conducted in the left hemisphere only. This approach provides a new avenue enabling the application of advanced neuroimaging analysis methods in quantifying brain damage in children with hydrocephalus surgically treated with programmable shunts.

•

We studied the structural connectivity of left hemisphere brain network in children with hydrocephalus post-surgery

•

Children with hydrocephalus post-surgery had significantly abnormal structural connectivity in the left hemisphere based on graph analysis

•

Significant correlation was found between graph measures at 3-months post-surgery and developmental outcome at 12-month post-surgery

Diffusion tensor imaging study of pediatric patients with congenital hydrocephalus: 1-year postsurgical outcomes

OBJECTIVE The purpose of this study was to investigate white matter (WM) structural abnormalities using diffusion tensor imaging (DTI) in children with hydrocephalus before CSF diversionary surgery (including ventriculoperitoneal shunt insertion and endoscopic third ventriculostomy) and during the course of recovery after surgery in association with neuropsychological and behavioral outcome. METHODS This prospective study included 54 pediatric patients with congenital hydrocephalus (21 female, 33 male; age range 0.03-194.5 months) who underwent surgery and 64 normal controls (30 female, 34 male; age range 0.30-197.75 months). DTI and neurodevelopmental outcome data were collected once in the control group and 3 times (preoperatively and at 3 and 12 months postoperatively) in the patients with hydrocephalus. DTI measures, including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) values were extracted from the genu of the corpus callosum (gCC) and the posterior limb of internal capsule (PLIC). Group analysis was performed first cross-sectionally to quantify DTI abnormalities at 3 time points by comparing the data obtained in the hydrocephalus group for each of the 3 time points to data obtained in the controls. Longitudinal comparisons were conducted pairwise between different time points in patients whose data were acquired at multiple time points. Neurodevelopmental data were collected and analyzed using the Adaptive Behavior Assessment System, Second Edition, and the Bayley Scales of Infant Development, Third Edition. Correlation analyses were performed between DTI and behavioral measures. RESULTS Significant DTI abnormalities were found in the hydrocephalus patients in both the gCC (lower FA and higher MD, AD, and RD) and the PLIC (higher FA, lower AD and RD) before surgery. The DTI measures in the gCC remained mostly abnormal at 3 and 12 months after surgery. The DTI abnormalities in the PLIC were significant in FA and AD at 3 months after surgery but did not persist when tested at 12 months after surgery. Significant longitudinal DTI changes in the patients with hydrocephalus were found in the gCC when findings at 3 and 12 months after surgery were compared. In the PLIC, trend-level longitudinal changes were observed between preoperative findings and 3-month postoperative findings, as well as between 3- and 12-month postoperative findings. Significant correlation between DTI and developmental outcome was found at all 3 time points. Notably, a significant correlation was found between DTI in the PLIC at 3 months after surgery and developmental outcome at 12 months after surgery. CONCLUSIONS The data showed significant WM abnormality based on DTI in both the gCC and the PLIC in patients with congenital hydrocephalus before surgery, and the abnormalities persisted in both the gCC and the PLIC at 3 months after surgery. The DTI values remained significantly abnormal in the gCC at 12 months after surgery. Longitudinal analysis showed signs of recovery in both WM structures between different time points. Combined with the significant correlation found between DTI and neuropsychological measures, the findings of this study suggest that DTI can serve as a sensitive imaging biomarker for underlying neuroanatomical changes and postsurgical developmental outcome and even as a predictor for future outcomes.

Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease?

INTRODUCTION

Since its description five decades ago, the pathophysiology of idiopathic chronic adult hydrocephalus (iCAH) has been traditionally related to the effect that ventricular dilatation exerts on the structures surrounding the ventricular system. However, altered cerebral blood flow, especially a reduction in the CSF turnover rate, are starting to be considered the main pathophysiological elements of this disease.

DEVELOPMENT

Compression of the pyramidal tract, the frontostriatal and frontoreticular circuits, and the paraventricular fibres of the superior longitudinal fasciculus have all been reported in iCAH. At the level of the corpus callosum, gliosis replaces a number of commissural tracts. Cerebral blood flow is also altered, showing a periventricular watershed region limited by the subependymal arteries and the perforating branches of the major arteries of the anterior cerebral circulation. The CSF turnover rate is decreased by 75%, leading to the reduced clearance of neurotoxins and the interruption of neuroendocrine and paracrine signalling in the CSF.

CONCLUSIONS

iCAH presents as a complex nosological entity, in which the effects of subcortical microangiopathy and reduced CSF turnover play a key role. According to its pathophysiology, it is simpler to think of iCAH more as a neurodegenerative disease, such as Alzheimer disease or Binswanger disease than as the classical concept of hydrocephalus.

The influence of surgical correction on white matter microstructural integrity in rabbits with familial coronal suture craniosynostosis

OBJECT Craniosynostosis is a condition in which one or more of the calvarial sutures fuses prematurely. In addition to the cosmetic ramifications attributable to premature suture fusion, aberrations in neurophysiological parameters are seen, which may result in more significant damage. This work examines the microstructural integrity of white matter, using diffusion tensor imaging (DTI) in a homogeneous strain of rabbits with simple, familial coronal suture synostosis before and after surgical correction. METHODS After diagnosis, rabbits were assigned to different groups: wild-type (WT), rabbits with early-onset complete fusion of the coronal suture (BC), and rabbits that had undergone surgical correction with suturectomy (BC-SU) at 10 days of age. Fixed rabbit heads were imaged at 12, 25, or 42 days of life using a 4.7-T, 40-cm bore Avance scanner with a 7.2-cm radiofrequency coil. For DTI, a 3D spin echo sequence was used with a diffusion gradient (b = 2000 sec/mm(2)) applied in 6 directions. RESULTS As age increased from 12 to 42 days, the DTI differences between WT and BC groups became more pronounced (p < 0.05, 1-way ANOVA), especially in the corpus callosum, cingulum, and fimbriae. Suturectomy resulted in rabbits with no significant differences compared with WT animals, as assessed by DTI of white matter tracts. Also, it was possible to predict to which group an animal belonged (WT, BC, and BC-SU) with high accuracy based on imaging data alone using a linear support vector machine classifier. The ability to predict to which group the animal belonged improved as the age of the animal increased (71% accurate at 12 days and 100% accurate at 42 days). CONCLUSIONS Craniosynostosis results in characteristic changes of major white matter tracts, with differences becoming more apparent as the age of the rabbits increases. Early suturectomy (at 10 days of life) appears to mitigate these differences.

Longitudinal Changes in the Brain Following Third Ventriculostomy in a Child With Hydrocephalus: A Case Report

The goal of this study was to detect the long-term effect of shunting on the integrity of white matter in young children with hydrocephalus.The authors reported the case of a 6-month-old boy with hydrocephalus who was evaluated by diffusion tensor imaging (DTI) before and after a shunt operation.When compared with normal children, the structures of the corpus callosum, internal capsule, and corona radiata in the patient showed a decrease in fractional anisotropy and an increase in radial diffusivity values before the shunt operation. Following successful cerebrospinal fluid shunting, long-term follow-up DTI demonstrated a trend toward normalization of the fractional anisotropy and radial diffusivity values.Shunt treatment can prevent further damage to the brain and grossly reconstitute the distorted anatomy. DTI could be a useful tool in detecting longitudinal changes after a shunt operation. Further studies involving larger case numbers are needed to detect the long-term effect of shunting on the brains of children with hydrocephalus.

Clinical benefits of diffusion tensor imaging in hydrocephalus

OBJECT The object of this study was to use diffusion tensor imaging (DTI) to evaluate and characterize white matter changes in hydrocephalus. METHODS The authors performed a retrospective analysis of DTI in a cohort of patients with hydrocephalus (n = 35), 19 of whom had both pre- and postsurgical imaging studies. These patient's DTI values were compared with values extracted from age-dependent trend lines computed from a healthy subject group (n = 70, age span 14 months-14 years). Several DTI parameters in different regions of interest (ROIs) were evaluated to find the most sensitive parameters for clinical decision making in hydrocephalus. RESULTS Compared with healthy controls, patients with active hydrocephalus had a statistically significant change in all DTI parameters. The most sensitive and specific DTI parameter for predicting hydrocephalus was axial diffusivity (λ1) measured at the level of the corona radiata. Diffusion tensor imaging parameters correlated with several conventional radiological parameters in the assessment of hydrocephalus but were not superior to them. There was no convincing correlation between clinical disease severity and DTI parameters. When examining the pre- and postsurgical effect, it was found that DTI may be a sensitive tool for estimating tissue improvement. CONCLUSIONS This large-cohort study with a multidisciplinary approach combining clinical, neurological, radiological, and multiple DTI parameters revealed the most sensitive DTI parameters for identifying hydrocephalus and suggested that they may serve as an important tool for the disorder's quantitative radiological assessment.

Abnormal structural connectivity in the brain networks of children with hydrocephalus

Increased intracranial pressure and ventriculomegaly in children with hydrocephalus are known to have adverse effects on white matter structure. This study seeks to investigate the impact of hydrocephalus on topological features of brain networks in children. The goal was to investigate structural network connectivity, at both global and regional levels, in the brains in children with hydrocephalus using graph theory analysis and diffusion tensor tractography. Three groups of children were included in the study (29 normally developing controls, 9 preoperative hydrocephalus patients, and 17 postoperative hydrocephalus patients). Graph theory analysis was applied to calculate the global network measures including small-worldness, normalized clustering coefficients, normalized characteristic path length, global efficiency, and modularity. Abnormalities in regional network parameters, including nodal degree, local efficiency, clustering coefficient, and betweenness centrality, were also compared between the two patients groups (separately) and the controls using two tailed t-test at significance level of p < 0.05 (corrected for multiple comparison). Children with hydrocephalus in both the preoperative and postoperative groups were found to have significantly lower small-worldness and lower normalized clustering coefficient than controls. Children with hydrocephalus in the postoperative group were also found to have significantly lower normalized characteristic path length and lower modularity. At regional level, significant group differences (or differences at trend level) in regional network measures were found between hydrocephalus patients and the controls in a series of brain regions including the medial occipital gyrus, medial frontal gyrus, thalamus, cingulate gyrus, lingual gyrus, rectal gyrus, caudate, cuneus, and insular. Our data showed that structural connectivity analysis using graph theory and diffusion tensor tractography is sensitive to detect abnormalities of brain network connectivity associated with hydrocephalus at both global and regional levels, thus providing a new avenue for potential diagnosis and prognosis tool for children with hydrocephalus.

Postshunt lateral ventricular volume, white matter integrity, and intellectual outcomes in spina bifida and hydrocephalus

OBJECT

No previous reports exist that have evaluated the relationships of white matter (WM) integrity with the number of shunt revisions, ventricular volume after shunting, and cognition in medically stable children who have spina bifida and hydrocephalus (SBH). The authors hypothesized that enlarged ventricles and a greater number of shunt revisions decrease WM integrity in children.

METHODS

In total, 80 children (mean age 13.7 years) who had SBH underwent MRI and IQ testing. Probabilistic diffusion tractography was performed to determine mean diffusion tensor imaging (DTI) metrics along the frontal and parietal tectocortical pathways. The DTI metrics were evaluated for significant correlation with a composite IQ measure and with the total number of shunt revisions and the total lateral ventricular volume obtained through semiautomated parcellation of T1-weighted MRI scans.

RESULTS

An enlargement in total lateral ventricle volume and an increase in the number of shunt revisions were both associated with higher fractional anisotropy (FA) and with lower radial diffusivity (RD) along both frontal and parietal tectocortical pathways. Children who had not undergone a shunt revision had on average a greater lateral ventricle volume and higher FA and lower RD along frontal and parietal pathways than those who had undergone multiple shunt revisions. The mean DTI metrics along parietal pathways predicted IQ scores, but intellectual ability was not significantly correlated with ventricular volume or with the number of lifetime shunt revisions.

CONCLUSIONS

Significant changes in DTI metrics were observed as a function of ventricular volume. An increased lateral ventricle volume was associated with elevated FA and decreased RD. Given that the participants were medically stable at the time of the MRI examination, the results suggested that those who have enlarged ventricles show a DTI pattern consistent with axonal compression due to increased intracranial pressure (ICP) in attenuated hydrocephalus. Although limited by a cross-sectional design, the study's findings suggest that DTI metrics may serve as sensitive indicators for chronic, mild hydrocephalus in the absence of overt clinical symptoms due to increased ICP. Having enlarged ventricles and undergoing multiple shunt revisions did not affect intellectual ability in children with SBH.

Differential vulnerability of white matter structures to experimental infantile hydrocephalus detected by diffusion tensor imaging

PURPOSE

The differential vulnerability of white matter (WM) to acute and chronic infantile hydrocephalus and the related effects of early and late reservoir treatment are unknown, but diffusion tensor imaging (DTI) could provide this information. Thus, we characterized WM integrity using DTI in a clinically relevant model.

METHODS

Obstructive hydrocephalus was induced in 2-week-old felines by intracisternal kaolin injection. Ventricular reservoirs were placed 1 (early) or 2 (late) weeks post-kaolin and tapped frequently based solely on neurological deficit. Hydrocephalic and age-matched control animals were sacrificed 12 weeks postreservoir. WM integrity was evaluated in the optic system, corpus callosum, and internal capsule prereservoir and every 3 weeks using DTI. Analyses were grouped as acute (<6 weeks) or chronic (≥6 weeks).

RESULTS

In the corpus callosum during acute stages, fractional anisotropy (FA) decreased significantly with early and late reservoir placement (p = 0.0008 and 0.0008, respectively), and diffusivity increased significantly in early (axial, radial, and mean diffusivity, p = 0.0026, 0.0012, and 0.0002, respectively) and late (radial and mean diffusivity, p = 0.01 and 0.0038, respectively) groups. Chronically, the corpus callosum was thinned and not detectable by DTI. FA was significantly lower in the optic chiasm and tracts (p = 0.0496 and 0.0052, respectively) with late but not early reservoir placement. In the internal capsule, FA in both reservoir groups increased significantly with age (p < 0.05) but diffusivity remained unchanged.

CONCLUSIONS

All hydrocephalic animals treated with intermittent ventricular reservoir tapping demonstrated progressive ventriculomegaly. Both reservoir groups demonstrated WM integrity loss, with the CC the most vulnerable and the optic system the most resilient.

Structural brain alterations in children an average of 5 years after surgery and chemotherapy for brain tumors

Young children with brain tumors are often treated with high-dose chemotherapy after surgery to avoid brain tissue injury associated with irradiation. The effects of systemic chemotherapy on healthy brain tissue in this population, however, are unclear. Our objective was to compare gray and white matter integrity using MRI procedures in children with brain tumors (n = 7, mean age 8.3 years), treated with surgery and high-dose chemotherapy followed by autologous hematopoietic cell rescue (AuHCR) an average of 5.4 years earlier, to age- and gender-matched healthy controls (n = 9, mean age 9.3 years). Diffusion tensor imaging data were collected to evaluate tissue integrity throughout the brain, as measured by mean diffusivity (MD), a marker of glial, neuronal, and axonal status, and fractional anisotropy (FA), an index of axonal health. Individual MD and FA maps were calculated, normalized, smoothed, and compared between groups using analysis of covariance, with age and sex as covariates. Higher MD values, indicative of injury, emerged in patients compared with controls (p < .05, corrected for multiple comparisons), and were especially apparent in the central thalamus, external capsule, putamen, globus pallidus and pons. Reduced FA values in some regions did not reach significance after correction for multiple comparisons. Children treated with surgery and high-dose chemotherapy with AuHCR for brain tumors an average of 5.4 years earlier show alterations in white and gray matter in multiple brain areas distant from the tumor site, raising the possibility for long-term consequences of the tumor or treatment.

Kaolin-induced ventriculomegaly at weaning produces long-term learning, memory, and motor deficits in rats

Ventriculomegaly occurs when there is imbalance between creation and absorption of cerebrospinal fluid (CSF); even when treated, long-term behavioral changes occur. Kaolin injection in the cisterna magna of rats produces an obstruction of CSF outflow and models one type of hydrocephalus. Previous research with this model shows that neonatal onset has mixed effects on Morris water maze (MWM) and motoric performance; we hypothesized that this might be because the severity of ventricular enlargement was not taken into consideration. In the present experiment, rats were injected with kaolin or saline on postnatal day (P)21 and analyzed in subgroups based on Evan's ratios (ERs) of the severity of ventricular enlargement at the end of testing to create 4 subgroups from least to most severe: ER0.4-0.5, ER0.51-0.6, ER0.61-0.7, and ER0.71-0.82, respectively. Locomotor activity (dry land and swimming), acoustic startle with prepulse inhibition (PPI), and MWM performance were tested starting on P28 (122cm maze) and again on P42 (244cm maze). Kaolin-treated animals weighed significantly less than controls at all times. Differences in locomotor activity were seen at P42 but not P28. On P28 there was an increase in PPI for all but the least severe kaolin-treated group, but no difference at P42 compared with controls. In the MWM at P28, all kaolin-treated groups had longer path lengths than controls, but comparable swim speeds. With the exception of the least severe group, probe trial performance was worse in the kaolin-treated animals. On P42, only the most severely affected kaolin-treated group showed deficits compared with control animals. This group showed no MWM learning and no memory for the platform position during probe trial testing. Swim speed was unaffected, indicating motor deficits were not responsible for impaired learning and memory. These findings indicate that kaolin-induced ventriculomegaly in rats interferes with cognition regardless of the final enlargement of the cerebral ventricles, but final size critically determines whether lasting locomotor, learning, and memory impairments occur.

Diffusion tensor imaging properties and neurobehavioral outcomes in children with hydrocephalus

BACKGROUND AND PURPOSE

White matter structural alterations and the correlation with neuropsychological deficits in children with hydrocephalus have not been well investigated. In this prospective study, the objectives were the following: 1) to apply DTI to detect in vivo white matter alterations based on diffusion properties in children with acute hydrocephalus, 2) to quantify early neuropsychological deficits, and 3) to explore the correlation between potential neuropsychological deficits and abnormalities in functionally related white matter.

MATERIALS AND METHODS

A total of 44 children, 24 with hydrocephalus and 20 controls, were enrolled in the study. DTI indices, FA, MD, AD, and RD, were evaluated in the gCC, sCC, PLIC, and ALIC. The ABAS-II was used as a broad screener of development, including conceptual, social, practical, and motor skills. The correlation between the Motor Scale and DTI indices in the PLIC was analyzed.

RESULTS

DTI analyses showed that the gCC and sCC in children with hydrocephalus had lower FA and higher MD, driven by the increased RD with statistical significance (P < .05) or trend-level significance (P = .06). The PLIC and ALIC had significantly higher AD in children with hydrocephalus (P < .05). On the ABAS-II, parent ratings of general adaptive skills, conceptual skills, and motor skills were significantly lower in children with hydrocephalus (all at P < .05). The MD and RD values in the PLIC were found to have trend-level or significant correlation with the Motor Scale (P = .057, .041, respectively).

CONCLUSIONS

DTI reveals alterations in the white matter structure in children with hydrocephalus with preliminary findings suggesting correlation with clinical motor deficits.

DTI values in key white matter tracts from infancy through adolescence

BACKGROUND AND PURPOSE

DTI is an advanced neuroimaging technique that allows in vivo quantification of water diffusion properties as surrogate markers of the integrity of WM microstructure. In our study, we investigated normative data from a large number of pediatric and adolescent participants to examine the developmental trends in DTI during this conspicuous WM maturation period.

MATERIALS AND METHODS

DTI data in 202 healthy pediatric and adolescent participants were analyzed retrospectively. Fractional anisotropy and mean diffusivity values in the corpus callosum and internal capsule were fitted to an exponential regression model to delineate age-dependent maturational changes across the WM structures.

RESULTS

The DTI metrics demonstrated characteristic exponential patterns of progression during development and conspicuous age-dependent changes in the first 36 months, with rostral WM tracts experiencing the highest slope of the exponential function. In contrast, the highest final FA and lowest MD values were detected in the splenium of the corpus callosum and the posterior limb of the internal capsule.

CONCLUSIONS

Our analysis shows that the more caudal portions of the corpus callosum and internal capsule begin the maturation process earlier than the rostral regions, but the rostral regions develop at a more accelerated pace, which may suggest that rostral regions rely on development of more caudal brain regions to instigate their development. Our normative DTI can be used as a reference to study normal spatiotemporal developmental profiles in the WM and help identify abnormal WM structures in patient populations.

Diffusion tensor imaging in hydrocephalus--findings before and after shunt surgery

BACKGROUND

To evaluate changes in diffusion tensor imaging (DTI)-derived parameters in patients with hydrocephalus (HC) before and several weeks after shunt surgery.

METHODS

Thirteen HC patients were examined with DTI before and after shunt surgery. In a combined region of interest and whole brain voxel-based analysis, different DTI parameters were compared with an age-matched control group.

RESULTS

Alteration of DTI parameters in HC patients and changes after shunt surgery are regionally different. HC patients show an increase in fractional anisotropy values based on increases in parallel diffusivity in the corticospinal tract. On the other hand, reduced fractional anisotropy values are found in the corpus callosum of HC patients. Following shunt surgery, all DTI parameters showed a trend towards normalization, yet differences to healthy control subjects remained.

CONCLUSION

Our results show that DTI parameter changes are regionally dependent and need a careful interpretation of the underlying diffusivities to serve as a diagnostic or follow-up measure in patients with hydrocephalus.

Longitudinal comparison of diffusion tensor imaging parameters and neuropsychological measures following endoscopic third ventriculostomy for hydrocephalus

The authors report the case of a 25-month-old boy who underwent endoscopic third ventriculostomy (ETV) for hydrocephalus resulting from aqueductal stenosis. The patient's recovery was monitored longitudinally and prospectively using MR diffusion tensor imaging (DTI) and formal neuropsychological testing. Despite minimal change in ventricle size, improvement in the DTI characteristics and neurodevelopmental trajectory was observed following ETV. These data support the use of DTI as a biomarker to assess therapeutic response in children undergoing surgical treatment for hydrocephalus. In the patient featured in this report, DTI appeared to provide more information regarding postoperative neurodevelopmental outcome than ventricle size alone.

Diffusion tensor imaging findings in young children with benign external hydrocephalus differ from the normal population

PURPOSE

To compare a pediatric population diagnosed with benign external hydrocephalus (BEH) to normal age-matched controls using diffusion tensor imaging (DTI) techniques.

METHODS

We retrospectively identified 17 BEH patients by specific clinical and neuroimaging criteria. Fractional anisotropy (FA) and mean diffusivity (MD) values obtained from DTI scans were compared to a population of age-matched controls and group differences were examined by mixed model analysis. A longitudinal comparison was completed on a subset that underwent multiple scans (n = 8).

RESULTS

In the genu of the corpus callosum (gCC), six of 15 BEH children had an FA value above the upper limit of 95% prediction interval, nine of 15 BEH children had MD values below the lower limit of 95% prediction interval. A similar trend applied to the other regions of interest (ROIs): splenium of the corpus callosum (sCC), ALIC, and PLIC. Statistical analysis demonstrated significant differences in FA within the gCC, sCC, and PLIC and in MD within the sCC between BEH patients and controls given (P = 0.05). No statistical differences were identified at any ROIs at the later scans.

CONCLUSIONS

We found a significant increase in FA and decrease in MD in children with BEH compared with normal children in specific white matter (WM) ROIs, notably in the gCC and sCC; furthermore, in longitudinal comparison, DTI parameters normalized over time. The current study further demonstrates the ability of DTI to distinguish between subtle diffusion changes in periventricular white matter and establishes preliminary objective radiographic parameters for watchful observation of patients with BEH.

Diffusion tensor imaging of white matter injury in a rat model of infantile hydrocephalus

OBJECTIVE

Diffusion tensor imaging (DTI) is a non-invasive MRI technique that has been used to quantify white matter (WM) abnormality in both clinical and experimental hydrocephalus (HCP). However, no DTI study has been conducted to characterize anisotropic diffusion properties in an animal model of infantile HCP. This DTI study was designed to investigate a rat model of HCP induced at postnatal day 21, a time developmentally equivalent to the human infancy.

METHODS

DTI data were acquired at approximately 4 weeks after the induction of HCP with kaolin injection. Using a 7 Tesla small animal MRI scanner we performed high-resolution DTI on 12 rats with HCP and 6 saline controls. Regions of interest (ROI) examined with quantitative comparisons include the genu, body, and splenium of the corpus callosum (gCC, bCC, and sCC, respectively), anterior, middle, and posterior external capsule (aEC, mEC, and pEC, respectively), internal capsule (IC), and fornix (FX). For each ROI, DTI metrics including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (Dax), and radial diffusivity (Drad) were calculated.

RESULTS

We found that the anisotropic diffusion properties were abnormal across multiple WM regions in the brains of the HCP rats. Statistically significant differences included: (1) decreased FA and increased MD and Drad values in the gCC and bCC; (2) increased Dax in the sCC; (3) increased FA and Dax in the aEC; (4) increased FA in the mEC; (5) increased MD and Drad in the pEC; (6) increased FA and Dax in IC; (7) increased FA in FX.

CONCLUSIONS

These preliminary results provide the first evidence of WM injury quantified by DTI in a rat model of infantile HCP. Our data showed that DTI is a sensitive tool to characterize patterns of WM abnormalities and support the notion that WM impairment is region specific in response to HCP.

Diffusion tensor imaging reveals supplementary lesions to frontal white matter in idiopathic normal pressure hydrocephalus

BACKGROUND

Idiopathic normal-pressure hydrocephalus (INPH) is associated with white matter lesions, but the extent and severity of the lesions do not cohere with symptoms or improvement after shunting, implying the presence of further, yet undisclosed, injuries to white matter in INPH.

OBJECTIVE

To apply diffusion tensor imaging (DTI) to explore white matter lesions in patients with INPH before and after drainage of cerebrospinal fluid (CSF).

METHODS

Eighteen patients and 10 controls were included. DTI was performed in a 1.5T MRI scanner before and after 3-day drainage of 400 mL of CSF. Regions of interest included corpus callosum, capsula interna, frontal and lateral periventricular white matter, and centrum semiovale. White matter integrity was quantified by assessing fractional anisotropies (FA) and apparent diffusion coefficients (ADC), comparing them between patients and controls and between patients before and after drainage. The significance level corresponded to .05 (Bonferroni corrected).

RESULTS

Decreased FA in patients was found in 3 regions (P<.002, P<.001, and P<.001) in anterior frontal white matter, whereas elevated ADC was found in genu corpus callosum (P<.001) and areas of centrum semiovale associated with the precentral gyri (P<.002). Diffusion patterns in these areas did not change after drainage.

CONCLUSION

DTI reveals subtle injuries-interpreted as axonal loss and gliosis-to anterior frontal white matter where high-order motor systems between frontal cortex and basal ganglia travel, further supporting the notion that motor symptoms in INPH are caused by a chronic ischemia to the neuronal systems involved in the planning processes of movements.

Diffusion tensor imaging evaluation of white matter in adolescents with myelomeningocele and Chiari II malformation

BACKGROUND

Macrostructural abnormalities in cerebral white matter in patients with myelomeningocele are well known, but microstructural abnormalities are not as well studied.

OBJECTIVE

The aim of this study was to evaluate cerebral white matter in adolescents with myelomeningocele using diffusion tensor imaging (DTI), and to investigate the effects of ventricular dilation and CSF shunt presence on white matter microstructure in these patients.

MATERIALS AND METHODS

DTI and T1-weighted 3-D (T1-3-D) MRI were performed on nine adolescents with myelomeningocele and Chiari II malformation and nine age-matched controls. The fractional anisotropy (FA) and mean diffusivity (MD) values were measured and compared.

RESULTS

Significantly decreased FA and increased MD values were observed in most white matter regions and fibers in adolescents with myelomeningocele compared to controls. Further analysis in patients revealed significant changes in DTI parameters in hemispheres with enlarged lateral ventricles compared to those with normal ventricle size. In addition, a significant difference in FA values in the posterior limb of the internal capsule was found in the comparison of hemispheres in patients with or without CSF shunt catheters.

CONCLUSION

This study revealed widespread microstructural abnormalities in white matter in adolescents with myelomeningocele and Chiari II malformation. Ventricular dilation may have additional effects on white matter microstructure in this patient population. CSF shunt diversion effects on white matter may be multifactorial and need further investigation.

Negative-pressure and low-pressure hydrocephalus: the role of cerebrospinal fluid leaks resulting from surgical approaches to the cranial base

OBJECT

Negative-pressure and low-pressure hydrocephalus are rare clinical entities that are frequently misdiagnosed. They are characterized by recurrent episodes of shunt failure because the intracranial pressure is lower than the opening pressure of the valve. In this report the authors discuss iatrogenic CSF leaks as a cause of low- or negative-pressure hydrocephalus after approaches to the cranial base.

METHODS

The authors retrospectively reviewed cases of low-pressure or negative-pressure hydrocephalus presenting after cranial approaches complicated with a CSF leak at their institution.

RESULTS

Three patients were identified. Symptoms of high intracranial pressure and ventriculomegaly were present, although the measured pressures were low or negative. A blocked communication between the ventricles and the subarachnoid space was documented in 2 of the cases and presumed in the third. Shunt revisions failed repeatedly. In all cases, temporary clinical and radiographic improvement resulted from external ventricular drainage at subatmospheric pressures. The CSF leaks were sealed and CSF communication was reestablished operatively. In 1 case, neck wrapping was used with temporary success.

CONCLUSIONS

Negative-pressure or low-pressure hydrocephalus associated with CSF leaks, especially after cranial base approaches, is difficult to treat. The solution often requires the utilization of subatmospheric external ventricular drains to establish a lower ventricular drainage pressure than the drainage pressure created in the subarachnoid space, where the pressure is artificially lowered by the CSF leak. Treatment involves correction of the CSF leak, neck wrapping to increase brain turgor and allow the pressure in the ventricles to rise to the level of the opening pressure of the valve, and reestablishing the CSF route.

Diffusion tensor imaging correlates with cytopathology in a rat model of neonatal hydrocephalus

Background

Diffusion tensor imaging (DTI) is a non-invasive MRI technique that has been used to quantify CNS abnormalities in various pathologic conditions. This study was designed to quantify the anisotropic diffusion properties in the brain of neonatal rats with hydrocephalus (HCP) and to investigate association between DTI measurements and cytopathology.

Methods

DTI data were acquired between postnatal day 7 (P7) and P12 in 12 rats with HCP induced at P2 and in 15 age-matched controls. Animals were euthanized at P11 or P22/P23 and brains were processed with immunohistochemistry for glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule (Iba-1), and luxol fast blue (LFB) to assess astrocytosis, microglial reactivity and degree of myelination, respectively.

Results

Hydrocephalic rats were consistently found to have an abnormally low (at corrected p-level of <0.05) fractional anisotropy (FA) value and an abnormally high mean diffusivity (MD) value in the cerebral cortex (CX), the corpus callosum (CC), and the internal capsule (IC). Immunohistochemical analysis demonstrated trends of increasing astrocyte and microglial reactivity in HCP rats at P11 that reached statistical significance at P22/P23. A trend toward reduced myelination in the HCP rats was also found at P22/P23. Correlation analysis at P11 for the CC demonstrated statistically significant correlations (or trends) between the DTI measurement (the decreased FA and increased MD values) and the GFAP or Iba-1 rankings. The immunohistochemical rankings in the IC at P22/P23 were also significantly correlated or demonstrated a trend with both FA and MD values.

Conclusions

This study demonstrates the feasibility of employing DTI on the brain in experimental hydrocephalus in neonatal rats and reveals impairments in multiple regions of interest in both grey and white matter. A strong correlation was found between the immunohistochemical results and the changes in anisotropic diffusion properties.