White and Gray Matter Abnormalities After Cranial Radiation in Children and Mice

Multimodal imaging with magnetization transfer and diffusion tensor imaging reveals evidence of myelin damage in children and youth treated for a brain tumor

Background

The microstructural damage underlying compromise of white matter following treatment for pediatric brain tumors is unclear. We use multimodal imaging employing advanced diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI) MRI methods to examine chronic microstructural damage to white matter in children and adolescents treated for pediatric brain tumor. Notably, MTI may be more sensitive to macromolecular content, including myelin, than DTI.

Methods

Fifty patients treated for brain tumors (18 treated with surgery ± chemotherapy and 32 treated with surgery followed by cranial-spinal radiation; time from diagnosis to scan ~6 years) and 45 matched healthy children completed both MTI and DTI scans. Voxelwise and region-of-interest approaches were employed to compare white matter microstructure metrics (magnetization transfer ratio (MTR); DTI- fractional anisotropy [FA], radial diffusivity [RD], axial diffusivity [AD], mean diffusivity [MD]) between patients and healthy controls.

Results

MTR was decreased across multiple white matter tracts in patients when compared to healthy children, P < .001. These differences were observed for both patients treated with radiation and those treated with only surgery, P < .001. We also found that children and adolescents treated for brain tumors exhibit decreased FA and increased RD/AD/MD compared to their healthy counterparts in several white matter regions, Ps < .02. Finally, we observed that MTR and DTI metrics were related to multiple white matter tracts in patients, Ps < .01, but not healthy control children.

Conclusions

Our findings provide evidence that the white matter damage observed in patients years after treatment of pediatric posterior fossa tumors, likely reflects myelin disruption.

Total-Body Irradiation Alters White Matter Volume and Microstructural Integrity in Rhesus Macaques

PURPOSE

Long-term survivors of brain irradiation can experience irreversible injury and cognitive impairment. T1-weighted and diffusion tensor magnetic resonance imaging (MRI) are used to evaluate brain volume and white matter (WM) microstructure in neurodevelopmental and neurodegenerative conditions. The goal of this study was to evaluate the long-term effects of single-dose total-body irradiation (TBI) or TBI with 5% partial-body sparing on brain volumetrics and WM integrity in macaques.

METHODS AND MATERIALS

We used MRI scans from a cohort of male rhesus macaques (age range, 3.6-22.8 years) to compare global and regional brain volumes and WM diffusion in survivors of TBI (T1-weighted, n = 137; diffusion tensor imaging, n = 121; dose range, 3.5-10 Gy) with unirradiated controls (T1-weighted, n = 48; diffusion tensor imaging, n = 38).

RESULTS

In all regions of interest, radiation affected age-related changes in fractional anisotropy, which tended to increase across age in both groups but to a lesser extent in the irradiated group (interaction P < .01). Depending on the region of interest, mean diffusivity decreased or remained the same across age in unirradiated animals, whereas it increased or did not change in irradiated animals. The increases in mean diffusivity were driven by changes in radial diffusivity, which followed similar trends across age. Axial diffusivity did not differ by irradiation status. Age-related changes in relative volumes in controls reflected normal trends in humans, with increasing WM and decreasing gray matter until middle age. Cerebrospinal fluid (CSF) volume did not differ across age in controls. WM volume was lower and CSF volume was higher in young irradiated macaques. WM volume was similar between groups, and CSF volume lower in older irradiated macaques. Gray matter volume was unaffected by radiation.

CONCLUSIONS

TBI results in delayed WM expansion and long-term disruption of WM integrity. Diffusion changes suggest that myelin injury in WM is a hallmark of late-delayed radiation-induced brain injury.

Exercise promotes growth and rescues volume deficits in the hippocampus after cranial radiation in young mice

Human and animal studies suggest that exercise promotes healthy brain development and function, including promoting hippocampal growth. Childhood cancer survivors that have received cranial radiotherapy exhibit hippocampal volume deficits and are at risk of impaired cognitive function, thus they may benefit from regular exercise. While morphological changes induced by exercise have been characterized using magnetic resonance imaging (MRI) in humans and animal models, evaluation of changes across the brain through development and following cranial radiation is lacking. In this study, we used high-resolution longitudinal MRI through development to evaluate the effects of exercise in a pediatric mouse model of cranial radiation. Female mice received whole-brain radiation (7 Gy) or sham radiation (0 Gy) at an infant equivalent age (P16). One week after irradiation, mice were housed in either a regular cage or a cage equipped with a running wheel. In vivo MRI was performed prior to irradiation, and at three subsequent timepoints to evaluate the effects of radiation and exercise. We used a linear mixed-effects model to assess volumetric and cortical thickness changes. Exercise caused substantial increases in the volumes of certain brain regions, notably the hippocampus in both irradiated and nonirradiated mice. Volume increases exceeded the deficits induced by cranial irradiation. The effect of exercise and irradiation on subregional hippocampal volumes was also characterized. In addition, we characterized cortical thickness changes across development and found that it peaked between P23 and P43, depending on the region. Exercise also induced regional alterations in cortical thickness after 3 weeks of voluntary exercise, while irradiation did not substantially alter cortical thickness. Our results show that exercise has the potential to alter neuroanatomical outcomes in both irradiated and nonirradiated mice. This supports ongoing research exploring exercise as a strategy for improving neurocognitive development for children, particularly those treated with cranial radiotherapy.

Cognitive Sparing in Proton versus Photon Radiotherapy for Pediatric Brain Tumor Is Associated with White Matter Integrity: An Exploratory Study

Radiotherapy for pediatric brain tumors is associated with reduced white matter structural integrity and neurocognitive decline. Superior cognitive outcomes have been reported following proton radiotherapy (PRT) compared to photon radiotherapy (XRT), presumably due to improved sparing of normal brain tissue. This exploratory study examined the relationship between white matter change and late cognitive effects in pediatric brain tumor survivors treated with XRT versus PRT. Pediatric brain tumor survivors treated with XRT (n = 10) or PRT (n = 12) underwent neuropsychological testing and diffusion weighted imaging >7 years post-radiotherapy. A healthy comparison group (n = 23) was also recruited. Participants completed age-appropriate measures of intellectual functioning, visual-motor integration, and motor coordination. Tractography was conducted using automated fiber quantification (AFQ). Fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) were extracted from 12 tracts of interest. Overall, both white matter integrity (FA) and neuropsychological performance were lower in XRT patients while PRT patients were similar to healthy control participants with respect to both FA and cognitive functioning. These findings support improved long-term outcomes in PRT versus XRT. This exploratory study is the first to directly support for white matter integrity as a mechanism of cognitive sparing in PRT.

Insult to Short-Range White Matter Connectivity in Childhood Brain Tumor Survivors

PURPOSE

Children treated for brain tumors are at an increased risk for cognitive impairments due to the effect of radiation therapy on developing white matter (WM). Although damage to long-range WM is well documented in pediatric brain tumor survivors, the effect of radiation therapy on short-range WM remains unelucidated. We sought to clarify whether radiation treatment affects short-range WM by completing a virtual dissection of these connections and comparing their microstructural properties between brain tumor survivors and typically developing children.

METHODS AND MATERIALS

T1-weighted and diffusion-weighted magnetic resonance images were acquired for 26 brain tumor survivors and 26 typically developing children. Short-range WM was delineated using a novel, whole-brain approach. A random forest classifier was used to identify short-range connections with the largest differences in microstructure between patients and typically developing children.

RESULTS

The random forest classifier identified differences in short-range WM microstructure across the brain with an accuracy of 87.5%. Nine connections showed the largest differences in short-range WM between patients and typically developing children. For these connections, fractional anisotropy and axial diffusivity were significantly lower in patients. Short-range connections in the posterior fossa were disproportionately affected, suggesting that greater radiation exposure to the posterior fossa was more injurious to short-range WM. Lower craniospinal radiation dose did not predict reduced toxicity to short-range WM.

CONCLUSIONS

Our findings indicate that treatment for medulloblastoma resulted in changes in short-range WM in patients. Lower fractional anisotropy and axial diffusivity may reflect altered microstructural organization and coherence of these connections, especially in the posterior fossa. Short-range WM may be especially sensitive to the effect of craniospinal radiation therapy, resulting in compromise to these connections regardless of dose.

Volumetric changes in gray matter after radiotherapy detected with longitudinal magnetic resonance imaging in glioma patients

BACKGROUND AND PURPOSE

We evaluated volumetric changes in the gray matter (GM) after radiotherapy (RT) and identified factors that were strongly associated with GM volume reduction.

MATERIALS AND METHODS

A total of 461 magnetic resonance imagings (MRI) from 105 glioma patients treated with postoperative RT was retrospectively analyzed. Study patients' MRIs were collected at five time points: before RT and 1 month, 6 months, 1 year, and 2 years after RT. Using the 'FastSurfer' platform, a deep learning-based neuroimaging pipeline, 73 regions were automatically segmented from longitudinal MRIs and their volumetric changes were calculated. Regions were grouped into 10 functional fields. A multivariable linear mixed-effects model was established to identify the potential predictors of significant volume reduction.

RESULTS

The median age was 50 years (range, 16-86 years). Forty-seven (44.8 %) patients were female and 68 (64.8 %) had glioblastoma. Postoperative RT was delivered at 54-60 Gy with or without concurrent chemotherapy. At 2 years after RT, the median volumetric changes in the overall, ipsilateral, and contralateral GM were -3.5%, -4.5%, and -2.4%, respectively. The functional fields of cognition and execution of movement showed the greatest volume reductions. In the multivariable linear mixed model, female sex (normalized coefficient = -0.14, P < 0.001) and the interaction between age at RT and days after RT (normalized coefficient = -6.48e-6, P < 0.001) were significantly associated with GM reduction. The older patients received RT, the greater volume reduction was seen over time. However, in patients with relatively younger age (e.g., 45, 50, and 60 years for hippocampus, Broca area, and Wernicke area, respectively), the volume was not significantly reduced.

CONCLUSIONS

GM volume reduction was identified after RT that could lead to long-term treatment sequelae. Particularly for susceptible patients, individualized treatment and prevention strategies are needed.

Mini-Review: Aplastic Myelin Following Chemotherapy

The contribution of chemotherapy to improved outcomes for cancer patients is unquestionable. Yet as its applications broaden, so do the concerns for the long-term implications of chemotherapy on the health of cancer survivors, with chemotherapy-related cognitive impairment as a cause for particular urgency. In this mini review, we explore myelin aplasticity following chemotherapy, discussing the role of myelin plasticity in healthy cognition and failure of myelin plasticity chiefly due microenvironmental aberrations in chemotherapy-related cognitive impairment. Possible therapeutic strategies to mitigate chemotherapy-induced myelin dysfunction are also discussed.

Cross-translational models of late-onset cognitive sequelae and their treatment in pediatric brain tumor survivors

Pediatric brain tumor treatments have a high success rate, but survivors are at risk of cognitive sequelae that impact long-term quality of life. We summarize recent clinical and animal model research addressing pathogenesis or evaluating candidate interventions for treatment-induced cognitive sequelae. Assayed interventions encompass a broad range of approaches, including modifications to radiotherapy, modulation of immune response, prevention of treatment-induced cell loss or promotion of cell renewal, manipulation of neuronal signaling, and lifestyle/environmental adjustments. We further emphasize the potential of neuroimaging as a key component of cross-translation to contextualize laboratory research within broader clinical findings. This cross-translational approach has the potential to accelerate discovery to improve pediatric cancer survivors' long-term quality of life.

Abnormalities of Structural Brain Connectivity in Pediatric Brain Tumor Survivors

Background

Pediatric brain tumor survivors are at an increased risk for white matter (WM) injury. However, damage to whole-brain structural connectivity is unelucidated. The impact of treatment on WM connectivity was investigated.

Methods

Whole-brain WM networks were derived from diffusion tensor imaging data acquired for 28 irradiated patients (radiotherapy, RT) (mean age = 13.74 ± 3.32 years), 13 patients not irradiated (No RT) (mean age = 12.57 ± 2.87), and 41 typically developing children (TDC) (mean age = 13.32 ± 2.92 years). Differences in network properties were analyzed using robust regressions.

Results

Participation coefficient was lower in both patient groups (RT: adj. P = .015; No RT: adj. P = .042). Compared to TDC, RT had greater clustering (adj. P = .015), local efficiency (adj. P = .003), and modularity (adj. P = .000003). WM traced from hubs was damaged in patients: left hemisphere pericallosal sulcus (FA [F = 4.97; q < 0.01]; MD [F = 11.02; q < 0.0001]; AD [F = 10.00; q < 0.0001]; RD [F = 8.53; q < 0.0001]), right hemisphere pericallosal sulcus (FA [F = 8.87; q < 0.0001]; RD [F = 8.27; q < 0.001]), and right hemisphere parietooccipital sulcus (MD [F = 5.78; q < 0.05]; RD [F = 5.12; q < 0.05]).

Conclusions

Findings indicate greater segregation of WM networks after RT. Intermodular connectivity was lower after treatment with and without RT. No significant network differences were observed between patient groups. Our results are discussed in the context of a network approach that emphasizes interactions between brain regions.

High replication stress and limited Rad51-mediated DNA repair capacity, but not oxidative stress, underlie oligodendrocyte precursor cell radiosensitivity

Cranial irradiation is part of the standard of care for treating pediatric brain tumors. However, ionizing radiation can trigger serious long-term neurologic sequelae, including oligodendrocyte and brain white matter loss enabling neurocognitive decline in children surviving brain cancer. Oxidative stress-mediated oligodendrocyte precursor cell (OPC) radiosensitivity has been proposed as a possible explanation for this. Here, however, we demonstrate that antioxidants fail to improve OPC viability after irradiation, despite suppressing oxidative stress, suggesting an alternative etiology for OPC radiosensitivity. Using systematic approaches, we find that OPCs have higher irradiation-induced and endogenous γH2AX foci compared to neural stem cells, neurons, astrocytes and mature oligodendrocytes, and these correlate with replication-associated DNA double strand breakage. Furthermore, OPCs are reliant upon ATR kinase and Mre11 nuclease-dependent processes for viability, are more sensitive to drugs increasing replication fork collapse, and display synthetic lethality with PARP inhibitors after irradiation. This suggests an insufficiency for homology-mediated DNA repair in OPCs—a model that is supported by evidence of normal RPA but reduced RAD51 filament formation at resected lesions in irradiated OPCs. We therefore propose a DNA repair-centric mechanism of OPC radiosensitivity, involving chronically-elevated replication stress combined with ‘bottlenecks’ in RAD51-dependent DNA repair that together reduce radiation resilience.

Protection from radiation-induced neuroanatomical deficits by CCL2-deficiency is dependent on sex

PURPOSE

Cranial radiation therapy for the treatment of paediatric brain tumours results in changes to brain development that are detectable with magnetic resonance imaging (MRI). We have previously demonstrated similar structural changes in both humans and mice. The goal of the current study was to examine the role of inflammation in this response. Since neuroanatomical volume deficits in paediatric survivors are more pronounced in females, we also evaluated possible dependence on sex.

EXPERIMENTAL DESIGN

Male mice deficient in the C-C chemokine ligand 2 gene (Ccl2; previously Mcp-1) have been shown by others to have a muted neuroinflammatory response after irradiation. We irradiated Ccl2^-/- (HOM; females[f]=12, males[m]=13), Ccl2^+/- (HET; f=13, m=16), and Ccl2^+/+ (WT; f=11, m=13) mice with a whole brain dose of 7 Gy during infancy. Control mice (with approximately equal groups sizes) were anaesthetized but not irradiated. In vivo MR images were acquired at 4 time points up to 3 months following irradiation, and deformation-based morphometry was used to identify volume differences.

RESULTS

Irradiation of WT mice resulted in a deficit in neuroanatomical growth with limited sex dependence. HOM and HET males were significantly protected from this radiation-induced damage, while HOM and HET females were not. We conclude that interventions aimed at mitigating the effects of cranial radiation therapy in paediatric cancer survivors by modulating inflammatory response will need to consider patient sex.

Better detection of reduced motor functioning in brain tumor survivors based on objective motor assessments: an incentive for improved standardized follow-up

Long-term sequelae are well-known in childhood brain tumor survivors, but motor functioning remains poorly described. This cross-sectional study aimed to assess objective motor functioning, patient-specific risk factors, and parental perceptions. Fifty-two childhood brain tumor patients (pilocytic astrocytoma, medulloblastoma, and other types) who were at least 6 months out of treatment were evaluated. Mean age at testing was 11.7 years. Objective motor functioning was assessed with the Movement Assessment Battery for Children (MABC-2-NL) and/or Bruininks-Oseretsky test of motor proficiency (BOT-2). Functional walking capacity was assessed with the 6-min walk test (6MWT). Parent-reported motor functioning was addressed using the ABILHAND-Kids, ABILOCO-Kids questionnaires, and a standardized anamnesis. Patients showed impaired motor functioning in all domains (p < 0.001). Regarding risk factors, younger age at diagnosis (< 5 year) was significantly associated with lower scores on body coordination (p = 0.006). Adjuvant treatment resulted in lower scores for fine manual control of the BOT-2 (p = 0.024) and balance of MABC-2-NL (p = 0.036). Finally, questionnaires revealed an underestimation of motor problems as perceived by the parents. In conclusion, many children who are in follow-up for a brain tumor show impaired motor functioning on multiple aspects, with younger age at diagnosis and adjuvant treatment as specific risk factors. Based on the questionnaires and anamnesis, motor problems appear to be underestimated by the parents.  Conclusion: These findings point to the need for timely prospective screening of motor functioning. Based on a screening assessment, adequate rehabilitation programs can be applied in childhood brain tumor survivors, aiming to reduce the adverse impact on their daily lives, both for functional activities and cardiovascular fitness. What is Known: • A pediatric brain tumor and its treatment are associated with potential long-term motor sequelae. • Test assessments could enable us to objectify motor functioning of these patients. What is New: • Pediatric brain tumors survivors show lower motor performance compared to the norm, which is often underestimated by parents. • Younger age at diagnosis and adjuvant treatment could be specific risk factors.

Characterizing academic performance in pediatric acute lymphoblastic leukemia with population-based achievement tests

BACKGROUND

Recent shifts from radiation to chemotherapy-based treatment for acute lymphoblastic leukemia (ALL) have contributed to reduced long-term morbidity. Despite this, ALL survivors remain at increased risk for long-term cognitive impairments.

AIM

To identify demographic and treatment factors associated with school performance in pediatric survivors of ALL.

METHODS

We collected standardized test scores for reading, math, and science obtained in a school setting from grades 3-11 in 63 ALL survivors (46.0% boys). Most participants were assessed across multiple grades (median number of grades n = 5, range 1-7), and 269 observations were considered in the analyses. Treatment exposures were extracted from medical records. Socio-economic status was estimated using participation in free/reduced lunch programs at school. Mixed effects linear regression models were conducted to determine factors associated with school performance.

RESULTS

ALL survivors' scores were comparable to state norms on reading, math, and science performances. On multivariable analysis, participation in free/reduced lunch programs was significantly associated with lower reading scores (β = -12.52; 95% CI -22.26:-2.77, p = .01). Exposure to radiation during treatment was also associated with lower reading test scores (β = -30.81, 95% CI -52.00:-9.62, p = .01). No significant associations between demographics and treatment parameters were observed for math and science test scores.

CONCLUSIONS

We utilized population-based achievement tests conducted from grades 3-11 to characterize school performance in ALL survivors. Our results imply that survivors with low socio-economic status and those exposed to radiation during treatment could benefit from early monitoring and intervention to maximize academic success.

Metformin effects on brain development following cranial irradiation in a mouse model

BACKGROUND

Cranial radiation therapy (CRT) is a mainstay of treatment for malignant pediatric brain tumors and high-risk leukemia. Although CRT improves survival, it has been shown to disrupt normal brain development and result in cognitive impairments in cancer survivors. Animal studies suggest that there is potential to promote brain recovery after injury using metformin. Our aim was to evaluate whether metformin can restore brain volume outcomes in a mouse model of CRT.

METHODS

C57BL/6J mice were irradiated with a whole-brain radiation dose of 7 Gy during infancy. Two weeks of metformin treatment started either on the day of or 3 days after irradiation. In vivo magnetic resonance imaging was performed prior to irradiation and at 3 subsequent time points to evaluate the effects of radiation and metformin on brain development.

RESULTS

Widespread volume loss in the irradiated brain appeared within 1 week of irradiation with limited subsequent recovery in volume outcomes. In many structures, metformin administration starting on the day of irradiation exacerbated radiation-induced injury, particularly in male mice. Metformin treatment starting 3 days after irradiation improved brain volume outcomes in subcortical regions, the olfactory bulbs, and structures of the brainstem and cerebellum.

CONCLUSIONS

Our results show that metformin treatment has the potential to improve neuroanatomical outcomes after CRT. However, both timing of metformin administration and subject sex affect structure outcomes, and metformin may also be deleterious. Our results highlight important considerations in determining the potential benefits of metformin treatment after CRT and emphasize the need for caution in repurposing metformin in clinical studies.

Spatiotemporal Mapping of Early Volume Loss in the Mouse Brain after Cranial Irradiation

Sequelae after pediatric cranial radiotherapy (CRT) result in long-term changes in brain structure. While past evidence indicates regional differences in brain volume change, it remains unclear how these manifest in the time course of change after CRT. In this study, we spatiotemporally characterized volume losses induced by cranial irradiation in a mouse model, with a dense sampling of measurements over the first week postirradiation. Wild-type mice received whole-brain irradiation (7 Gy) or sham irradiation (0 Gy) at 16 days of age. In vivo magnetic resonance imaging was performed at one time point before, and 2-4 time points postirradiation in each mouse, with a particular focus on sampling during the first week after cranial irradiation. Volume changes across the brain were measured, and the degree and timing of volume loss were quantified across structures from a predefined atlas. Volume measurements across the brain after cranial irradiation revealed a ∼2-day delay in which volume is not significantly altered, after which time volume change proceeds over the course of four days. Volume losses were 3% larger and emerged 40% slower in white matter than in gray matter. Large volume loss was also observed in the ventricles. Differences in the timing and magnitude of volume change between gray and white matter after cranial irradiation were observed. These results suggest differences in the mechanism and/or kinetics underlying the associated radio-response, which may have implications in development.

Regional Responses in Radiation-Induced Normal Tissue Damage

Normal tissue side effects remain a major concern in radiotherapy. The improved precision of radiation dose delivery of recent technological developments in radiotherapy has the potential to reduce the radiation dose to organ regions that contribute the most to the development of side effects. This review discusses the contribution of regional variation in radiation responses in several organs. In the brain, various regions were found to contribute to radiation-induced neurocognitive dysfunction. In the parotid gland, the region containing the major ducts was found to be critical in hyposalivation. The heart and lung were each found to exhibit regional responses while also mutually affecting each other's response to radiation. Sub-structures critical for the development of side effects were identified in the pancreas and bladder. The presence of these regional responses is based on a non-uniform distribution of target cells or sub-structures critical for organ function. These characteristics are common to most organs in the body and we therefore hypothesize that regional responses in radiation-induced normal tissue damage may be a shared occurrence. Further investigations will offer new opportunities to reduce normal tissue side effects of radiotherapy using modern and high-precision technologies.

Neuroimaging Biomarkers and Neurocognitive Outcomes in Pediatric Medulloblastoma Patients: a Systematic Review

Medulloblastoma is a malign posterior fossa brain tumor, mostly occurring in childhood. The CNS-directed chemoradiotherapy treatment can be very harmful to the developing brain and functional outcomes of these patients. However, what the underlying neurotoxic mechanisms are remain inconclusive. Hence, this review summarizes the existing literature on the association between advanced neuroimaging and neurocognitive changes in patients that were treated for pediatric medulloblastoma. The PubMed/Medline database was extensively screened for studies investigating the link between cognitive outcomes and multimodal magnetic resonance (MR) imaging in childhood medulloblastoma survivors. A behavioral meta-analysis was performed on the available IQ scores. A total of 649 studies were screened, of which 22 studies were included. Based on this literature review, we conclude medulloblastoma patients to be at risk for white matter volume loss, more frequent white matter lesions, and changes in white matter microstructure. Such microstructural alterations were associated with lower IQ, which reached the clinical cut-off in survivors across studies. Using functional MR scans, changes in activity were observed in cerebellar areas, associated with working memory and processing speed. Finally, cerebral microbleeds were encountered more often, but these were not associated with cognitive outcomes. Regarding intervention studies, computerized cognitive training was associated with changes in prefrontal and cerebellar activation and physical training might result in microstructural and cortical alterations. Hence, to better define the neural targets for interventions in pediatric medulloblastoma patients, this review suggests working towards neuroimaging-based predictions of cognitive outcomes. To reach this goal, large multimodal prospective imaging studies are highly recommended.

Exercise interventions preserve hippocampal volume: A meta-analysis

Hippocampal volume is a marker of brain health and is reduced with aging and neurological disease. Exercise may be effective at increasing and preserving hippocampal volume, potentially serving as a treatment for conditions associated with hippocampal atrophy (e.g., dementia). This meta-analysis aimed to identify whether exercise training has a positive effect on hippocampal volume and how population characteristics and exercise parameters moderate this effect. Studies met the following criteria: (a) controlled trials; (b) interventions of physical exercise; (c) included at least one time-point of hippocampal volume data before the intervention and one after; (d) assessed hippocampal volume using either manual or automated segmentation algorithms. Animal studies, voxel-based morphometry analyses, and multi-modal interventions (e.g., cognitive training or meditation) were excluded. The primary analysis in n = 23 interventions from 22 published studies revealed a significant positive effect of exercise on total hippocampal volume. The overall effect was significant in older samples (65 years of age or older) and in interventions that lasted over 24 weeks and had less than 150 min per week of exercise. These findings suggest that moderate amounts of exercise for interventions greater than 6 months have a positive effect on hippocampal volume including in older populations vulnerable to hippocampal atrophy.

Quantitative MRI outcomes in child and adolescent leukemia survivors: Evidence for global alterations in gray and white matter

•

Studies of cognition in ALL survivors consistently show evidence of mild neurocognitive difficulties.

•

Structural MRI showed widespread differences between survivors and controls.

•

Gray and white matter volumes were respectively 5 and 6% smaller in survivors.

•

Survivors also exhibited altered white matter diffusion overall.

Introduction

Cure rates for pediatric acute lymphoblastic leukemia (ALL) have reached an all-time high (>90%); however, neurocognitive difficulties continue to affect quality of life in at least a subset of survivors. There are relatively few quantitative neuroimaging studies in child and adolescent ALL survivors treated with chemotherapy only. Use of different outcome measures or limited sample sizes restrict our ability to make inferences about patterns of brain development following chemotherapy treatment. In this study, we used magnetic resonance imaging (MRI) to evaluate brain outcomes in ALL survivors, comparing against a group of typically developing, cancer free peers.

Materials and methods

Participants included 71 ALL survivors, on average 8 years after diagnosis and 8–18 years of age, and 83 typically developing controls. Anatomical MRI was performed to evaluate brain structure; diffusion and magnetization transfer MRI were used to examine brain tissue microstructure.

Results

Successful MRI scans were acquired in 67 survivors (94%) and 82 controls (99%). Structurally, ALL survivors exhibited widespread reductions in brain volume, with 6% less white matter and 5% less gray matter than controls (p = 0.003 and 0.0006 respectively). Much of the brain appeared affected – 71 of 90 evaluated structures showed smaller volume – with the most notable exception being the occipital lobe, where no significant differences were observed. Average full-scale IQ in the survivor and control groups were 95 (CI 92–99) and 110 (CI 107–113), respectively. Using data from the NIH Pediatric MRI Data Repository, we evaluated the extent to which elevated IQ in the control group might affect the structural differences observed. We estimated that two thirds of the observed brain differences were attributable to ALL and its treatment. In addition to the structural changes, survivors showed, on average, globally lower white matter fractional anisotropy (-3%) and higher radial diffusivity (+5%) (p < 10⁻⁶), but no differences in magnetization transfer ratio.

Conclusions

Neuroanatomical alterations in late childhood and adolescent ALL survivors treated with chemotherapy-only protocols are widespread, with white matter being somewhat more affected than gray matter. These MRI results indicate brain development is altered in ALL survivors and highlight the need to examine how these alterations emerge.

Slit-like hypertensive hydrocephalus: Report of a late, complex, and multifactorial complication in an oncologic patient

Background:

Several sophisticated techniques and many chemotherapy drugs have improved life expectancy of oncologic patients allowing us to observe late complications which present many years after the initial treatment.

Case Description:

We present a unique case of a patient affected by acute lymphoblastic leukemia at the age of 6 years, treated with whole brain radiotherapy and intrathecal chemotherapy, developing meningiomatosis and leptomeningeal alterations as late complications and the interaction of these two entities caused a peculiar form of hydrocephalus without ventricular dilation. The diagnosis of pseudotumor cerebri was excluded due the postradio/chemotherapy development of meningiomatosis, not present in a previously head magnetic resonance imaging, that exerted compression to the Sylvian aqueduct causing intracranial hypertension with papillary stasis without ventricles enlargement due to brain stiffness. Moreover, a peculiar intraoperative rubbery consistency of brain parenchyma was detected strengthening this complex diagnosis.

Conclusion:

At the best of our knowledge, this is the first report of obstructive hydrocephalus without ventricles dilation caused by brain stiffness related to late alterations of oncologic treatments. This report could be a guide for further complex patients diagnoses and for improving treatments efficacy.

Delayed effects of a single-dose whole-brain radiation therapy on glucose metabolism and myelin density: a longitudinal PET study

PURPOSE

Radiotherapy is an important treatment option for brain tumors, but the unavoidable irradiation of normal brain tissue can lead to delayed cognitive impairment. The mechanisms involved are still not well explained and, therefore, new tools to investigate the processes leading to the delayed symptoms of brain irradiation are warranted. In this study, positron emission tomography (PET) is used to explore delayed functional changes induced by brain irradiation.

MATERIALS AND METHODS

Male Wistar rats were subjected to a single 25-Gy dose of whole brain X-ray irradiation, or sham-irradiation. To investigate delayed effects of radiation on cerebral glucose metabolism and myelin density, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET scans were performed at baseline and on day 64 and 94, whereas N-¹¹C-methyl-4,4'-diaminostilbene (¹¹C-MeDAS) PET scans were performed at baseline and on day 60 and 90 post-irradiation. In addition, the open field test (OFT) and novel spatial recognition (NSR) test were performed at baseline and on days 59 and 89 to investigate whether whole brain irradiation induces behavioral changes.

RESULTS

Whole-brain irradiation caused loss of bodyweight and delayed cerebral hypometabolism, with ¹⁸F-FDG uptake in all brain regions being significantly decreased in irradiated rat on day 64 while it remained unchanged in control animals. Only amygdala and cortical brain regions of irradiated rats still showed reduced ¹⁸F-FDG uptake on day 94. ¹¹C-MeDAS uptake in control animals was significantly lower on days 60 and 90 than at the baseline, suggesting a reduction in myelin density in young adults. In irradiated animals, ¹¹C-MeDAS uptake was similarly reduced on day 60, but on day 90 tracer uptake was somewhat increased and not significantly different from baseline anymore. Behavioral tests showed a similar pattern in control and irradiated animals. In both groups, the OFT showed significantly reduced mobility on days 59 and 89, whereas the NSR did not reveal any significant changes in spatial memory over time. Interestingly, a positive correlation between the NSR and ¹¹C-MeDAS uptake was observed in irradiated rats.

CONCLUSIONS

Whole-brain irradiation causes delayed brain hypometabolism, which is not accompanied by white matter loss. Irradiated animals showed similar behavioral changes over time as control animals and, therefore, cerebral hypometabolism could not be linked to behavioral abnormalities. However, spatial memory seems to be associated with myelin density in irradiated rats.

Neuropsychological outcomes on Head Start III: a prospective, multi-institutional clinical trial for young children diagnosed with malignant brain tumors

BACKGROUND

Current pediatric brain tumor treatment focuses on titrating toxicity based on risk factors while simultaneously improving survivorship. The Head Start (HS) protocols I to IV (1991-present) use high-dose chemotherapy (HDCTx) with an aim of reducing or eliminating cranial irradiation in very young children, the most vulnerable to its effects.

METHODS

We examined estimated Full Scale IQ, overall Adaptive Functioning, Working Memory, Processing Speed, and Verbal and Nonverbal Memory outcome data for 43 HS III patients diagnosed between ages 2 months and 7 years from 15 institutions in the United States and Canada.

RESULTS

At a mean of 5.12 years postdiagnosis, the HS III patients performed within the average to low-average ranges across these variables; however, individual variability was noted with scores ranging from superior to impaired, and the sample as a whole performed lower than age expectations. Performance did not significantly differ by sex or ethnicity, diagnosis, or for those treated with an intravenous methotrexate dose of 400 mg/kg vs 270 mg/kg. Additionally, performance did not significantly differ by age at diagnosis or length of follow-up.

CONCLUSIONS

The results, indicating overall average to low-average neurocognitive functioning, are encouraging, though significant individual variability was noted. Those who were younger at diagnosis, received more intensive methotrexate, and were further out from treatment were not at significantly increased risk of cognitive decline within our sample, suggesting a strategy of using HDCTx and autologous hematopoietic progenitor cell rescue to reduce or eliminate irradiation may allow for continued CNS development in young children treated for a brain tumor.

Emerging mechanistic underpinnings and therapeutic targets for chemotherapy-related cognitive impairment

PURPOSE OF REVIEW

Modern innovations in cancer therapy have dramatically increased the number of cancer survivors. An unfortunately frequent side-effect of cancer treatment is enduring neurological impairment. Persistent deficits in attention, concentration, memory, and speed of information processing afflict a substantial fraction of cancer survivors following completion of these life-saving therapies. Here, we highlight chemotherapy-related cognitive impairment (CRCI) and discuss the current understanding of mechanisms underlying CRCI.

RECENT FINDINGS

New studies emphasize the deleterious impact of chemotherapeutic agents on glial-glial and neuron-glial interactions that shape the form, function and plasticity of the central nervous system. An emerging theme in cancer therapy-related cognitive impairment is therapy-induced microglial activation and consequent dysfunction of both neural precursor cells and mature neural cell types. Recent work has highlighted the complexity of dysregulated intercellular interactions involving oligodendrocyte lineage cells, microglia, astrocytes, and neurons following exposure to traditional cancer therapies such as methotrexate. This new understanding of the mechanistic underpinnings of CRCI has elucidated potential therapeutic interventions, including colony-stimulating factor 1 receptor inhibition, TrkB agonism, and aerobic exercise.

SUMMARY

Traditional cancer therapies induce lasting alterations to multiple neural cell types. Therapy-induced microglial activation is a critical component of the cause of CRCI, contributing to dysregulation of numerous processes of neural plasticity. Therapeutic targeting of microglial activation or the consequent dysregulation of neural plasticity mechanisms are emerging.

Predictors of neuropsychological late effects and white matter correlates in children treated for a brain tumor without radiation therapy

BACKGROUND

Little is known about cognition and predictors of neuropsychological outcomes in pediatric low-grade glioma (PLGG) survivors treated without radiation therapy. This research expands upon our previous work by further identifying the cognitive profile of PLGG patients treated without radiation therapy, investigating the specific medical and demographic variables that predict functioning, and examining white matter structure and its relationship to neuropsychological performance.

PROCEDURE

Nineteen PLGG patients (11-19 years) were administered the Wechsler Intelligence Scale for Children/Wechsler Adult Intelligence Scale, and subtests from the Woodcock-Johnson Tests of Cognition (visual matching, rapid picture naming, and pair cancellation) and Cambridge Neuropsychological Test Automated Battery (pattern recognition memory, delayed matching to sample, intra-extra dimensional set shift, motor screening task, rapid visual information processing, and spatial span).

RESULTS

The sample had normative weaknesses in verbal working memory, brief attention/vigilance, psychomotor speeded output, visual perception and matching, overall cognition, working memory, and processing speed. Increased surgeries or subtotal resections, hydrocephalus, shunting procedures, chemotherapy, NF1, and supratentorial location were predictive of cognitive deficits. Broad white matter involvement of the frontal, temporal, parietal, and occipital lobes as well as the cerebellum, as inferred from diffusion tensor imaging indices of decreased fiber orientation and increased water diffusion, was related to many cognitive difficulties.

CONCLUSIONS

This study comprehensively examines cognitive functioning in PLGG patients treated without radiation therapy, predictors of cognition, and its relation to white matter structure. Our findings indicate that medical and demographic variables other than radiation therapy can lead to cognitive late effects with diffuse white matter involvement.

Changes in cortical thickness and volume after cranial radiation treatment: A systematic review

Cognitive decline has a clear impact on quality of life in patients who have received cranial radiation treatment. The pathophysiological process is most likely multifactorial, with a possible role for decreased cortical thickness and volume. As radiotherapy treatment systems are becoming more sophisticated, precise sparing of vulnerable regions and tissue is possible. This allows radiation oncologists to make treatment more patient-tailored. A systematic search was performed to collect and review all available evidence regarding the effect of cranial radiation treatment on cortical thickness and volume. We searched the Pubmed, Embase and Cochrane databases, with an additional reference check in the Scopus database. Studies that examined cortical changes on MRI within patients as well as between treated and non-treated patients were included. The quality of the studies was assessed with a checklist specially designed for this review. No meta-analysis was performed due to the lack of randomised trials. Out of 1915 publications twenty-one papers were selected, of which fifteen observed cortical changes after radiation therapy. Two papers reported radiation-dependent decrease in cortical thickness within patients one year after radiation treatment, suggesting a clear relation between the two. However, study quality was considered mostly suboptimal, and there was great inhomogeneity between the included studies. This means that, although there has been increasing interest in the effects of radiation treatment on cortex morphology, no reliable conclusion can be drawn based on the currently available evidence. This calls for more research, preferably with a sufficiently large patient population, and adequate methodology.

Medulloblastoma

Medulloblastoma (MB) comprises a biologically heterogeneous group of embryonal tumours of the cerebellum. Four subgroups of MB have been described (WNT, sonic hedgehog (SHH), Group 3 and Group 4), each of which is associated with different genetic alterations, age at onset and prognosis. These subgroups have broadly been incorporated into the WHO classification of central nervous system tumours but still need to be accounted for to appropriately tailor disease risk to therapy intensity and to target therapy to disease biology. In this Primer, the epidemiology (including MB predisposition), molecular pathogenesis and integrative diagnosis taking histomorphology, molecular genetics and imaging into account are reviewed. In addition, management strategies, which encompass surgical resection of the tumour, cranio-spinal irradiation and chemotherapy, are discussed, together with the possibility of focusing more on disease biology and robust molecularly driven patient stratification in future clinical trials.

Altered brain morphology after focal radiation reveals impact of off-target effects: implications for white matter development and neurogenesis

Background

Children with brain tumors treated with cranial radiation therapy (RT) often exhibit cognitive late effects, commonly associated with reduced white matter (WM) volume and decreased neurogenesis. The impact of radiation damage in particular regions or tissues on brain development as a whole has not been elucidated.

Methods

We delivered whole-brain or focal radiation (8 Gy single dose) to infant mice. Focal treatments targeted white matter (anterior commissure), neuronal (olfactory bulbs), or neurogenic (subventricular zone) regions. High-resolution ex vivo MRI was used to assess radiation-induced volume differences. Immunohistochemistry for myelin basic protein and doublecortin was performed to assess associated cellular changes within white matter and related to neurogenesis, respectively.

Results

Both whole-brain and focal RT in infancy resulted in volume deficits in young adulthood, with whole-brain RT resulting in the largest deficits. RT of the anterior commissure, surprisingly, showed no impact on its volume or on brain development as a whole. In contrast, RT of the olfactory bulbs resulted in off-target volume reduction in the anterior commissure and decreased subventricular zone neurogenesis. RT of the subventricular zone likewise produced volume deficits in both the olfactory bulbs and the anterior commissure. Similar off-target effects were found in the corpus callosum and parietal cortex.

Conclusions

Our results demonstrate that radiation damage locally can have important off-target consequences for brain development. These data suggest that WM may be less radiosensitive than volume change alone would indicate and have implications for region-sparing radiation treatments aimed at reducing cognitive late effects.

Brain Development and Heart Function after Systemic Single-Agent Chemotherapy in a Mouse Model of Childhood Leukemia Treatment

PURPOSE

Chemotherapy for childhood acute lymphoblastic leukemia (ALL) can cause late-appearing side effects in survivors that affect multiple organs, including the heart and brain. However, the complex ALL treatment regimen makes it difficult to isolate the causes of these side effects and impossible to separate the contributions of individual chemotherapy agents by clinical observation. Using a mouse model, we therefore assessed each of eight representative, systemically-administered ALL chemotherapy agents for their impact on postnatal brain development and heart function.

EXPERIMENTAL DESIGN

Mice were treated systemically with a single chemotherapy agent at an infant equivalent age, then allowed to age to early adulthood (9 weeks). Cardiac structure and function were assessed using in vivo high-frequency ultrasound, and brain anatomy was assessed using high-resolution volumetric ex vivo MRI. In addition, longitudinal in vivo MRI was used to determine the time course of developmental change after vincristine treatment.

RESULTS

Vincristine, doxorubicin, and methotrexate were observed to produce the greatest deficiencies in brain development as determined by volumes measured on MRI, whereas doxorubicin, methotrexate, and l-asparaginase altered heart structure or function. Longitudinal studies of vincristine revealed widespread volume loss immediately following treatment and impaired growth over time in several brain regions.

CONCLUSIONS

Multiple ALL chemotherapy agents can affect postnatal brain development or heart function. This study provides a ranking of agents based on potential toxicity, and thus highlights a subset likely to cause side effects in early adulthood for further study.

p53 Loss Mitigates Early Volume Deficits in the Brains of Irradiated Young Mice

PURPOSE

Pediatric cranial radiation therapy results in lasting changes in brain structure. Though different facets of radiation response have been characterized, the relative contributions of each to altered development is unclear. We sought to determine the role of radiation-induced programmed cell death, as mediated by the Trp53 (p53) gene, on neuroanatomic development.

METHODS AND MATERIALS

Mice having a conditional knockout of p53 (p53KO) or wildtype p53 (WT) were irradiated with a whole-brain dose of 7 Gy (IR; n = 30) or 0 Gy (sham; n = 28) at 16 days of age. In vivo magnetic resonance imaging was performed before irradiation and at 4 time points after irradiation, until 3 months posttreatment, followed by ex vivo magnetic resonance imaging and immunohistochemistry. The role of p53 in development was assessed at 6 weeks of age in another group of untreated mice (n = 37).

RESULTS

Neuroanatomic development in p53KO mice was normal. After cranial irradiation, alterations in neuroanatomy were detectable in WT mice and emerged through 2 stages: an early volume loss within 1 week and decreased growth through development. In many structures, the early volume loss was partially mitigated by p53KO. However, p53KO had a neutral or negative impact on growth; thus, p53KO did not widely improve volume at endpoint. Partial volume recovery was observed in the dentate gyrus and olfactory bulbs of p53KO-IR mice, with corresponding increases in neurogenesis compared with WT-IR mice.

CONCLUSIONS

Although p53 is known to play an important role in mediating radiation-induced apoptosis, this is the first study to look at the cumulative effect of p53KO through development after cranial irradiation across the entire brain. It is clear that apoptosis plays an important role in volume loss early after radiation therapy. This early preservation alone was insufficient to normalize brain development on the whole, but regions reliant on neurogenesis exhibited a significant benefit.

Early changes in white matter predict intellectual outcome in children treated for posterior fossa tumors

Purpose

Prospective and longitudinal neuroimaging studies of posterior fossa tumors are scarce. Here we evaluate the early changes in white matter and intellectual outcome up to 3 years after diagnosis.

Patients and methods

Twenty-two children with posterior fossa tumors and 24 similarly-aged healthy children participated. Patients included: (a) 12 individuals who received surgery, cranial-spinal radiation (CSR), and focal radiation to the tumor bed (CSR group) and (b) 10 individuals who received local therapy, either surgery only or surgery and focal radiation to the tumor bed (Local group). Diffusion tensor imaging (DTI) and intelligence measures were obtained an average of 3 months after diagnosis and then at 12, 24, and 36 months later. DTI tractography and voxel-wise approaches were employed. The Neurological Predictor Scale was used to summarize the type and amount of treatment for PF tumor patients. Linear mixed modelling was used to evaluate group differences at baseline and changes over time in DTI metrics for both the specific white matter tracts and voxel-wise, as well as for intelligence measures.

Results

Based on tractography, patients treated with CSR had significantly higher Axial and Mean diffusivity in the cortical-spinal tracts (CST) 3 month after diagnosis – particularly on the right side, p < .003, compared to healthy children. Mean diffusivity in right CST decreased over time in this group of patients, p = .001. No differences compared to controls were evident in specific tracts for the Local group, p > .10. Voxel-wise analyses revealed multiple areas of white matter compromise in both patients groups. Notably, both patient groups had lower scores on intelligence measures compared to the Control group: The CSR group displayed lower performance 3 months following diagnosis, ps < 0.001, and their performance remained stable over time ps > 0.10, whereas the Local group displayed no differences at 3 months, ps> 0.10, but their performance declined over time, ps < 0.01. At baseline, higher MD in right CST predicted lower Perceptual Reasoning scores across all participants, p = .001. Furthermore, lower FA in left IFOF at baseline predicted decline in Processing Speed over time, p = .001. In patients, more aggressive treatment protocols and presence of mutism were related to lower performance on intelligence measures at baseline, ps < 0.04.

Conclusions

Children treated with CSR displayed diffuse white matter compromise and poor intellectual outcome shortly after radiation treatment. There was evidence of subsequent growth of white matter structure, but stable intellectual insult. Conversely, in children treated with either surgery only or surgery and focal radiation to the tumor bed we observed less compromise of white matter early following treatment and no intellectual insult compared to healthy children. However, declines in intellectual function were evident for these children, though their performance remained within the average normative range. Overall, results suggest that early intervention is necessary to circumvent these deficits.

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There are early deficits to intellect and white matter shortly after treatment

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Early deficits were observed only after cranial-spinal radiation

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Intellectual deficits are generally stable over time

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White matter indices, mutism, and treatment predicted intellectual outcome

Impaired Recent, but Preserved Remote, Autobiographical Memory in Pediatric Brain Tumor Patients

Medulloblastomas, the most common malignant brain tumor in children, are typically treated with radiotherapy. Refinement of this treatment has greatly improved survival rates in this patient population. However, radiotherapy also profoundly affects the developing brain and is associated with reduced hippocampal volume and blunted hippocampal neurogenesis. Such hippocampal (as well as extrahippocampal) abnormalities likely contribute to cognitive impairments in this population. While several aspects of memory have been examined in this population, the impact of radiotherapy on autobiographical memory has not previously been evaluated. Here we evaluated autobiographical memory in male and female patients who received radiotherapy for posterior fossa tumors (PFTs), including medulloblastoma, during childhood. Using the Children's Autobiographical Interview, we retrospectively assessed episodic and nonepisodic details for events that either preceded (i.e., remote) or followed (i.e., recent) treatment. For post-treatment events, PFT patients reported fewer episodic details compared with control subjects. For pretreatment events, PFT patients reported equivalent episodic details compared with control subjects. In a range of conditions associated with reduced hippocampal volume (including medial temporal lobe amnesia, mild cognitive impairment, Alzheimer's disease, temporal lobe epilepsy, transient epileptic amnesia, frontal temporal dementia, traumatic brain injury, encephalitis, and aging), loss of episodic details (even in remote memories) accompanies hippocampal volume loss. It is therefore surprising that pretreatment episodic memories in PFT patients with reduced hippocampal volume are retained. We discuss these findings in light of the anterograde and retrograde impact on memory of experimentally suppressing hippocampal neurogenesis in rodents.SIGNIFICANCE STATEMENT Pediatric medulloblastoma survivors develop cognitive dysfunction following cranial radiotherapy treatment. We report that radiotherapy treatment impairs the ability to form new autobiographical memories, but spares preoperatively acquired autobiographical memories. Reductions in hippocampal volume and cortical volume in regions of the recollection network appear to contribute to this pattern of preserved preoperative, but impaired postoperative, memory. These findings have significant implications for understanding disrupted mnemonic processing in the medial temporal lobe memory system and in the broader recollection network, which are inadvertently affected by standard treatment methods for medulloblastoma tumors in children.

Association of Neuronal Injury in the Genu and Body of Corpus Callosum After Cranial Irradiation in Children With Impaired Cognitive Control: A Prospective Study

PURPOSE

Brain radiation is associated with functional deficits in children. The purpose of this study was to examine white matter integrity as measured by diffusion tensor imaging and associations with region-specific radiation dose and neuropsychological functioning in children treated with cranial irradiation.

METHODS AND MATERIALS

A total of 20 patients and 55 age- and sex-matched controls were included in the present study. Diffusion tensor imaging and neuropsychological assessments were conducted at baseline and 6, 15, and 27 months after treatment. The neuropsychological assessment included motor dexterity, working memory, and processing speed. White matter regions were contoured, and the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were recorded for each participant. Linear mixed effects regression models were used to prospectively compare the associations among ADC, FA, radiation dose to contoured structures, and performance on the neuropsychological assessments over time.

RESULTS

The mean prescription dose was 44 Gy (range 12-54). Across visits, compared with the controls, the patients showed a significantly increased ADC across all selected regions and alterations in FA in the dorsal midbrain and corpus callosum (genu, splenium, body). An increased radiation dose to the genu and body of the corpus callosum was associated with alterations in ADC and FA and reduced neuropsychological performance, most notably motor speed and processing.

CONCLUSIONS

These prospective data suggest that subcortical white matter, especially the genu and body of the corpus callosum, could be regions with increased susceptibility to radiation-induced injury, with implications for cognitive function.

MRI to Assess Neurological Function

This article describes a detailed set of protocols for mouse brain imaging using MRI. We focus primarily on measuring changes in neuroanatomy, and provide both instructions for mouse preparation and details on image acquisition, image processing, and statistics. Practical details as well as theoretical considerations are provided. © 2018 by John Wiley & Sons, Inc.

Longitudinal changes in gray matter regions after cranial radiation and comparative analysis with whole body radiation: a DTI study

PURPOSE

Radiation-induced white matter changes are well known and vastly studied. However, radiation-induced gray matter alterations are still a research question. In the present study, these changes were assessed in a longitudinal manner using Diffusion Tensor Imaging (DTI) and further compared for cranial and whole body radiation exposure.

MATERIALS AND METHODS

Male mice (C57BL/6) were irradiated with cranial or whole body radiation followed by DTI study at 7T animal MRI system during predose, subacute and early delayed phases of radiation sickness. Fractional anisotropy (FA) and mean diffusivity (MD) values were obtained from brain's gray matter regions.

RESULTS

Decreased FA with increased MD was observed prominently in animals exposed to cranial radiation showing most changes at 8 months post irradiation. However, whole body radiation induced FA changes were mostly observed at 1 month post irradiation as compared to controls.

CONCLUSIONS

The differential response after whole body and cranial irradiation observed in the study depicts that radiation exposure of 5 Gy could induce permanent alterations in gray matter regions prominently as observed in Caudoputamen region at all the time points. Thus, our study has bolstered the role of DTI to probe microstructural changes in gray matter regions of brain after radiation exposure.

Repairing the brain with physical exercise: Cortical thickness and brain volume increases in long-term pediatric brain tumor survivors in response to a structured exercise intervention

There is growing evidence that exercise induced experience dependent plasticity may foster structural and functional recovery following brain injury. We examined the efficacy of exercise training for neural and cognitive recovery in long-term pediatric brain tumor survivors treated with radiation.

We conducted a controlled clinical trial with crossover of exercise training (vs. no training) in a volunteer sample of 28 children treated with cranial radiation for brain tumors (mean age = 11.5 yrs.; mean time since diagnosis = 5.7 yrs). The endpoints were anatomical T1 MRI data and multiple behavioral outcomes presenting a broader analysis of structural MRI data across the entire brain. This included an analysis of changes in cortical thickness and brain volume using automated, user unbiased approaches. A series of general linear mixed effects models evaluating the effects of exercise training on cortical thickness were performed in a voxel and vertex-wise manner, as well as for specific regions of interest. In exploratory analyses, we evaluated the relationship between changes in cortical thickness after exercise with multiple behavioral outcomes, as well as the relation of these measures at baseline.

Exercise was associated with increases in cortical thickness within the right pre and postcentral gyri. Other notable areas of increased thickness related to training were present in the left pre and postcentral gyri, left temporal pole, left superior temporal gyrus, and left parahippocampal gyrus. Further, we observed that compared to a separate cohort of healthy children, participants displayed multiple areas with a significantly thinner cortex prior to training and fewer differences following training, indicating amelioration of anatomical deficits. Partial least squares analysis (PLS) revealed specific patterns of relations between cortical thickness and various behavioral outcomes both after training and at baseline.

Overall, our results indicate that exercise training in pediatric brain tumor patients treated with radiation has a beneficial impact on brain structure. We argue that exercise training should be incorporated into the development of neuro-rehabilitative treatments for long-term pediatric brain tumor survivors and other populations with acquired brain injury. (ClinicalTrials.gov, NCT01944761)

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Exercise training in pediatric brain tumor patients treated with radiation results in changes in brain structure

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Exercise was associated with increased cortical thickness in several areas including motor and somatosensory cortex

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Fewer differences between patients and healthy controls in cortical thickness were seen following exercise training

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Specific patterns of relations between cortical thickness and behavior at a baseline and after exercise training were seen

Developmental trajectories of macroanatomical structures in common marmoset brain

Morphometry studies of human brain development have revealed characteristics of some growth patterns, such as gray matter (GM) and white matter (WM), but the features that make human neurodevelopment distinct from that in other species remain unclear. Studies of the common marmoset (Callithrix jacchus), a small New World primate, can provide insights into unique features such as cooperative behaviors complementary to those from comparative analyses using mouse and rhesus monkey. In the present study, we analyzed developmental patterns of GM, WM, and cortical regions with volume measurements using longitudinal sample (23 marmosets; 11 male, 12 female) between the ages of one and 30months. Regional analysis using a total of 164 magnetic resonance imaging datasets revealed that GM volume increased before puberty (5.4months), but subsequently declined until adulthood, whereas WM volume increased rapidly before stabilizing around puberty (9.9months). Cortical regions showed similar patterns of increase and decrease, patterns with global GM but differed in the timing of volume peak and degree of decline across regions. The progressive-regressive pattern detected in both global and cortical GM was well correlated to phases of synaptogenesis and synaptic pruning reported in previous marmoset studies. A rapid increase in WM in early development may represent a distinctive aspect of human neurodevelopment. These findings suggest that studies of marmoset brain development can provide valuable comparative information that will facilitate a deeper understanding of human brain growth and neurodevelopmental disorders.

Brain Perfusion and Diffusion Abnormalities in Children Treated for Posterior Fossa Brain Tumors

OBJECTIVE

To compare cerebral perfusion and diffusion in survivors of childhood posterior fossa brain tumor with neurologically normal controls and correlate differences with cognitive dysfunction.

STUDY DESIGN

We analyzed retrospectively arterial spin-labeled cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) in 21 patients with medulloblastoma (MB), 18 patients with pilocytic astrocytoma (PA), and 64 neurologically normal children. We generated ANCOVA models to evaluate treatment effects on the cerebral cortex, thalamus, caudate, putamen, globus pallidus, hippocampus, amygdala, nucleus accumbens, and cerebral white matter at time points an average of 5.7 years after original diagnosis. A retrospective review of patient charts identified 12 patients with neurocognitive data and in whom the relationship between IQ and magnetic resonance imaging variables was assessed for each brain structure.

RESULTS

Patients with MB (all treated with surgery, chemotherapy, and radiation) had significantly lower global CBF relative to controls (10%-23% lower, varying by anatomic region, all adjusted P?<?.05), whereas patients with PA (all treated with surgery alone) had normal CBF. ADC was decreased specifically in the hippocampus and amygdala of patients with MB and within the amygdala of patients with PA but otherwise remained normal after therapy. In the patients with tumor previously evaluated for IQ, regional ADC, but not CBF, correlated with IQ (R²?=?0.33-0.75).

CONCLUSIONS

The treatment for MB, but not PA, was associated with globally reduced CBF. Treatment in both tumor types was associated with diffusion abnormalities of the mesial temporal lobe structures. Despite significant perfusion abnormalities in patients with MB, diffusion, but not perfusion, correlated with cognitive outcomes.

Radiation-induced abnormal cortical thickness in patients with nasopharyngeal carcinoma after radiotherapy

Conventional MRI studies showed that radiation-induced brain necrosis in patients with nasopharyngeal carcinoma (NPC) in years after radiotherapy (RT) could involve brain gray matter (GM) and impair brain function. However, it is still unclear the radiation-induced brain morphological changes in NPC patients with normal-appearing GM in the early period after RT. In this study, we acquired high-resolution brain structural MRI data from three groups of patients, 22 before radiotherapy (pre-RT) NPC patients with newly diagnosed but not yet medically treated, 22 NPC patients in the early-delayed stage after radiotherapy (post-RT-ED), and 20 NPC patients in the late-delayed stage after radiotherapy (post-RT-LD), and then analyzed the radiation-induced cortical thickness alteration in NPC patients after RT. Using a vertex-wise surface-based morphometry (SBM) approach, we detected significantly decreased cortical thickness in the precentral gyrus (PreCG) in the post-RT-ED group compared to the pre-RT group. And the post-RT-LD group showed significantly increased cortical thickness in widespread brain regions, including the bilateral inferior parietal, left isthmus of the cingulate, left bank of the superior temporal sulcus and left lateral occipital regions, compared to the pre-RT group, and in the bilateral PreCG compared to the post-RT-ED group. Similar analysis with ROI-wise SBM method also found the consistent results. These results indicated that radiation-induced brain injury mainly occurred in the post-RT-LD group and the cortical thickness alterations after RT were dynamic in different periods. Our findings may reflect the pathogenesis of radiation-induced brain injury in NPC patients with normal-appearing GM and an early intervention is necessary for protecting GM during RT.

Brain structure, working memory and response inhibition in childhood leukemia survivors

INTRODUCTION

Survival rates for children with acute lymphoblastic leukemia (ALL) approach 95%. At the same time, there is growing concern that chemotherapy causes alterations in brain development and cognitive abilities. We performed MRI measurements of white and gray matter volume to explore how variation in brain structure may be related to cognitive abilities in ALL survivors and healthy controls.

METHODS

The sample included 24 male ALL survivors who had completed contemporary treatment 3-11 years prior, and 21 age- and sex-matched controls. Participants were between 8 and 18 years old. Working memory and motor response inhibition were measured with the N-Back and Stop Signal Tasks (SST), respectively. Participants underwent 3T structural MRI to assess white and gray matter volumes overall, lobe-wise, and in cortical and atlas-identified subcortical structures. Mental health was assessed with the Child Behavioral Checklist.

RESULTS

ALL survivors performed more poorly on measures of working memory and response inhibition than controls. Frontal and parietal white matter, temporal and occipital gray matter volume, and volumes of subcortical white and gray matter structures were significantly reduced in ALL survivors compared with controls. Significant structure-function correlations were observed between working memory performance and volume of the amygdala, thalamus, striatum, and corpus callosum. Response inhibition was correlated with frontal white matter volume. No differences were found in psychopathology.

CONCLUSIONS

Compared with controls, a reduction in volume across brain regions and tissue types, was detectable in ALL survivors years after completion of therapy. These structural alterations were correlated with neurocognitive performance, particularly in working memory. Confirming these observations in a larger, more representative sample of the population is necessary. Additionally, establishing the time course of these changes-and the treatment, genetic, and environmental factors that influence them-may provide opportunities to identify at-risk patients, inform the design of treatment modifications, and minimize adverse cognitive outcomes.

Age- and Brain Region-Specific Changes of Glucose Metabolic Disorder, Learning, and Memory Dysfunction in Early Alzheimer's Disease Assessed in APP/PS1 Transgenic Mice Using 18F-FDG-PET

Alzheimer’s disease (AD) is a leading cause of dementia worldwide, associated with cognitive deficits and brain glucose metabolic alteration. However, the associations of glucose metabolic changes with cognitive dysfunction are less detailed. Here, we examined the brains of APP/presenilin 1 (PS1) transgenic (Tg) mice aged 2, 3.5, 5 and 8 months using ¹⁸F-labed fluorodeoxyglucose (¹⁸F-FDG) microPET to assess age- and brain region-specific changes of glucose metabolism. FDG uptake was calculated as a relative standardized uptake value (SUVr). Morris water maze (MWM) was used to evaluate learning and memory dysfunction. We showed a glucose utilization increase in multiple brain regions of Tg mice at 2 and 3.5 months but not at 5 and 8 months. Comparisons of SUVrs within brains showed higher glucose utilization than controls in the entorhinal cortex, hippocampus, and frontal cortex of Tg mice at 2 and 3.5 months but in the thalamus and striatum at 3.5, 5 and 8 months. By comparing SUVrs in the entorhinal cortex and hippocampus, Tg mice were distinguished from controls at 2 and 3.5 months. In MWM, Tg mice aged 2 months shared a similar performance to the controls (prodromal-AD). By contrast, Tg mice failed training tests at 3.5 months but failed all MWM tests at 5 and 8 months, suggestive of partial or complete cognitive deficits (symptomatic-AD). Correlation analyses showed that hippocampal SUVrs were significantly correlated with MWM parameters in the symptomatic-AD stage. These data suggest that glucose metabolic disorder occurs before onset of AD signs in APP/PS1 mice with the entorhinal cortex and hippocampus affected first, and that regional FDG uptake increase can be an early biomarker for AD. Furthermore, hippocampal FDG uptake is a possible indicator for progression of Alzheimer’s cognition after cognitive decline, at least in animals.