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

Pediatric Hydrocephalus and the Primary Care Provider

Hydrocephalus is a pathologic condition that results in the disruption of normal cerebrospinal fluid flow dynamics often characterized by an increase in intracranial pressure resulting in an abnormal dilation of the ventricles. The goal of this article was to provide the necessary background information to understand the pathophysiology related to hydrocephalus, recognize the presenting signs and symptoms of hydrocephalus, identify when to initiate a workup with further studies, and understand the management of pediatric patients with a new and preexisting diagnosis of hydrocephalus.

Subarachnomegaly-venous congestion of infancy

PURPOSE

Multiple names within the literature refer to a clinical picture affecting infants and consisting of a large or fast growing head circumference with enlarged cortical subarachnoid spaces (CSAS) while cranial sutures are open. This myriad of terms demonstrates the confusion about the entity, that may even group together different etiological processes. In this review, we aim to shed light on this matter in an effort to restate the defining features of the clinical picture and sum the evidence and current understanding of its pathophysiology and related imaging findings.

METHODS

Extensive and updated review of the literature with special focus on defining features, clinical history with long term evaluation and pathophysiological process.

RESULTS

Functional and molecular CSF studies as well as clinical evidence challenges the common pathophysiological theory based on non-functional arachnoid villi. Conversely, there is increasing evidence supporting cerebro-venous system abnormalities as the main pathophysiological factor. Additionally, long term cohorts studies show that it may have subtle but irreversible neurodevelopmental consequences.

CONCLUSION

Subarachnomegaly is an age-related condition of the infancy with radiological enlargement of CSAS and often self limiting course. However, considering the evidence on pathophysiology as outlined herein and long term outcome reports, further research effort is needed to assess the consequences of venous outflow impairment and enlarged CSAS and how this relates to imaging findings and neurodevelopment test results later in life.

Examining perinatal subdural haematoma as an aetiology of extra-axial hygroma and chronic subdural haematoma

AIM

Benign external hydrocephalus (BEH), hygroma and chronic subdural haematoma are extra-axial fluid collections in infants. MRI studies have shown that almost half of all new-borns have perinatal subdural blood, generally referred to as subdural haematoma (SDH) or perinatal SDH. Epidemiologically there are striking similarities between chronic SDH and BEH in infants.

METHODS

Discussion of pathophysiological mechanisms for BEH and chronic SDH, based on existing literature.

RESULTS

Perinatal SDH is common, and we hypothesise that this condition in some infants develop into extra-axial fluid collections, known as hygroma, BEH or chronic subdural haematoma. The mechanism seems to be an intradural bleeding that creates an obstructive layer preventing normal CSF absorption. The site where the bleeding originates from and those areas enveloped in blood from the primary damaged area are prone to later rebleeds, seen as 'acute on chronic' haematomas. With steady production of CSF and the blockage, increased intracranial pressure drives the accelerated skull growth seen in many of these children.

CONCLUSION

Perinatal SDH hampers CSF absorption, possibly leading to BEH and chronic SDH, with a high risk of false accusations of abuse. Close monitoring of head circumference could prove vital in detecting children with this condition.

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.

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.

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.

Epidemiology of Benign External Hydrocephalus in Norway-A Population-Based Study

BACKGROUND

Benign external hydrocephalus is defined as a rapidly increasing head circumference (occipitofrontal circumference) with characteristic radiological findings of increased subarachnoid cerebrospinal fluid spaces on neuroimaging. The incidence of benign external hydrocephalus has not been previously reported, and there is no available information on the ratio of benign external hydrocephalus in the population of hydrocephalic children.

METHODS

This study is retrospective and population-based study, geographically covering two health regions in the southern half of Norway with a total mean population of 3.34 million in the ten-year study period, constituting approximately 75% of the Norwegian population. Children with a head circumference crossing two percentiles, or greater than the 97.5th percentile, and with typical imaging findings of enlarged frontal subarachnoid spaces with or without enlarged ventricles were included. Children were excluded if they had a history of head trauma, intracranial hemorrhage, central nervous system infection, other known causes of hydrocephalus, or were born preterm defined as birth before 37 weeks of gestation.

RESULTS

A total of 176 children fitting the criteria were identified, giving an incidence of 0.4 per 1000 live births. One hundred fifty-two (86.4%) of the patients were male, and mean age at referral was 7.3 months. Increasing head circumference was the main reason for referral in 158 (89.8%) patients and the only finding in 60 (34.1%) patients. Thirty-seven (21%) children had normal ventricles on imaging; the remainder had increased ventricular size. The incidence of pediatric hydrocephalus in Norway is reported to be 0.75 per 1000 live births, thus benign external hydrocephalus accounts for approximately 50% of hydrocephalic conditions in this population.

CONCLUSIONS

The incidence of benign external hydrocephalus was found to be 0.4 per 1000 live births in this population.

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.

Indications for the performance of neuroimaging in children

Pediatric neurology relies on ultrasound, computed tomography (CT), and magnetic resonance (MR) imaging. CT prevails in acute neurologic presentations, including traumatic brain injury (TBI), nontraumatic coma, stroke, and status epilepticus, because of easy availability, with images of diagnostic quality, e.g., to exclude hemorrhage, usually completed quickly enough to avoid sedation. Concerns over the risks of ionizing radiation mean re-imaging and higher-dose procedures, e.g., arteriography and venography, require justification. T1/T2-weighted imaging (T1/T2-WI) MR with additional sequences (arteriography, venography, T2*, spectroscopy, diffusion tensor, perfusion, diffusion- (DWI) and susceptibility-weighted imaging (SWI)) often clarifies the diagnosis, which may alter management in acute settings, as well as chronic conditions, e.g., epilepsy. Clinical acumen remains essential to avoid imaging, e.g., in genetic epilepsies or migrainous headaches responding to treatment, or to target sequences to specific diagnosis, e.g., T1/T2-WI for shunt dysfunction (with SWI for TBI); DWI, arteriography including neck vessels, and venography for acute hemiplegia or coma; coronal temporal cuts for partial epilepsy; or muscle imaging for motor delay. The risk of general anesthesia is low; "head-only" scanners may allow rapid MRI without sedation. Timely and accurate reporting, with discrepancy discussion between expert neuroradiologists, is important for management of the child and the family's expectations.

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.

Benign external hydrocephalus in infants. A single centre experience and literature review

External hydrocephalus (EH) is a benign clinical entity in which macrocephaly is associated with an increase in volume of the subarachnoid space, especially overlying both frontal lobes, and a normal or only slight increase in volume of the lateral ventricles. Several pathogenic hypotheses have been proposed but the most accredited theory seems to be delayed maturation of the arachnoid villi. There is a consensus that this is a benign entity, correlated to a familial predisposition and, in some cases, inheritance. CT and MRI are very important to make a diagnosis but also to establish the prognosis in patients who encounter the rare complications such as subdural haematomas. In conclusion, CT and MRI can provide a highly accurate diagnosis in these patients, allowing a preliminary assessment of the prognosis, particularly regarding the enlarged subarachnoid space limits and the "cortical vein" sign which can predict a further complication. These results are obtained with the same examination performed in a standard CT or MRI study of the brain and no injection of contrast medium is needed.

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.