Disrupted development and integrity of frontal white matter in patients treated for pediatric medulloblastoma

Using diffusion MRI to understand white matter damage and the link between brain microstructure and cognitive deficits in paediatric medulloblastoma patients

PURPOSE

Survivors of medulloblastoma face a range of challenges after treatment, involving behavioural, cognitive, language and motor skills. Post-treatment outcomes are associated with structural changes within the brain resulting from both the tumour and the treatment. Diffusion magnetic resonance imaging (MRI) has been used to investigate the microstructure of the brain. In this review, we aim to summarise the literature on diffusion MRI in patients treated for medulloblastoma and discuss future directions on how diffusion imaging can be used to improve patient quality.

METHOD

This review summarises the current literature on medulloblastoma in children, focusing on the impact of both the tumour and its treatment on brain microstructure. We review studies where diffusion MRI has been correlated with either treatment characteristics or cognitive outcomes. We discuss the role diffusion MRI has taken in understanding the relationship between microstructural damage and cognitive and behavioural deficits.

RESULTS

We identified 35 studies that analysed diffusion MRI changes in patients treated for medulloblastoma. The majority of these studies found significant group differences in measures of brain microstructure between patients and controls, and some of these studies showed associations between microstructure and neurocognitive outcomes, which could be influenced by patient characteristics (e.g. age), treatment, radiation dose and treatment type.

CONCLUSIONS

In future, studies would benefit from being able to separate microstructural white matter damage caused by the tumour, tumour-related complications and treatment. Additionally, advanced diffusion modelling methods can be explored to understand and describe microstructural changes to white matter.

Long term neuropsychological outcomes of a pediatric ETANTR brain tumor: A case study

Survivors of pediatric brain tumors are at high risk for long-term neuropsychological difficulties. In the current case study, we present longitudinal neuropsychological data spanning 10 years (from age 9 to 19 years) of a patient with a rare, very large, bifrontal, embryonal tumor with abundant neuropil and true rosettes (ETANTR), which is typically associated with poor survivorship and significant neurological impact. Results demonstrated that the patient had largely intact cognitive functioning with specific difficulties in executive functioning, fine motor skills, and adaptive functioning at her most recent neuropsychology 10-year follow-up. These results highlight outcomes for a patient with remarkable resiliency in the context of numerous risk factors (a very large tumor size, multi-modal treatment, and seizure history). Patient protective factors (a high level of cognitive reserve, family support, and appropriate comprehensive educational services) likely contributed to the patient's favorable neuropsychological outcome. The patient's age at brain tumor diagnosis (9 years) and associated treatment was at a critical period of development for emerging higher order cognitive functions which likely impacted acquisition of executive functioning skills and secondarily adaptive skill outcomes. Consequently, pediatric brain tumor survivors with ETANTR or other frontal tumors require targeted screening of executive functions and proactive interventions.

The long-term impact of irradiation on functional connectivity in brain circuits involved in memory processes after pediatric posterior fossa tumor

PURPOSE

Memory is one of the main specific cognitive domains impaired with attention and processing speed after a pediatric brain tumor. This work explored the long-term impact of radiotherapy in children with posterior fossa tumor (PFT) on brain connectivity in neural circuits involved in memory using resting-state functional magnetic resonance imaging (rs-fMRI).

METHODS

A total of 20 irradiated and 15 non-irradiated PFT survivors, and 21 healthy controls, prospectively included in the IMPALA study (NCT04324450), performed memory tests assessing episodic, procedural, and working memories and were subjected to an rs-fMRI. We manually contoured main structures involved in memory to explore connectivity at rest in a seed-to-voxel analysis. The groups were compared and differences in connectivity were correlated with behavioral scores and irradiation doses.

RESULTS

The performance of all mnesic tasks was lower in PFT survivors with a greater alteration in working and episodic memory in irradiated patients. Irradiated survivors had atypical connectivities in all memory circuits compared to controls and in cortico-caudate and cortico-cerebellar circuits compared to non-irradiated survivors. Non-irradiated survivors had only atypical connectivities in the cortico-cerebellar circuits compared to controls. In irradiated survivors, atypical connectivities in cortico-hippocampal circuits were linked with episodic memory scores and dose of irradiation to the left hippocampus and in cortico-striatal circuits with procedural memory scores and dose of irradiation to the striatum.

CONCLUSION

The results of this study highlight that irradiation has a long-term impact on brain connectivity in brain circuits involved in memory after pediatric PFT with a specific radiation-dose effect in supratentorial structures.

Neurocognitive Dysfunction After Treatment for Pediatric Brain Tumors: Subtype-Specific Findings and Proposal for Brain Network-Informed Evaluations

The increasing number of long-term survivors of pediatric brain tumors requires us to incorporate the most recent knowledge derived from cognitive neuroscience into their oncological treatment. As the lesion itself, as well as each treatment, can cause specific neural damage, the long-term neurocognitive outcomes are highly complex and challenging to assess. The number of neurocognitive studies in this population grows exponentially worldwide, motivating modern neuroscience to provide guidance in follow-up before, during and after treatment. In this review, we provide an overview of structural and functional brain connectomes and their role in the neuropsychological outcomes of specific brain tumor types. Based on this information, we propose a theoretical neuroscientific framework to apply appropriate neuropsychological and imaging follow-up for future clinical care and rehabilitation trials.

A high-dimensional mediation model for a neuroimaging mediator: Integrating clinical, neuroimaging, and neurocognitive data to mitigate late effects in pediatric cancer

Pediatric cancer treatment, especially for brain tumors, can have profound and complicated late effects. With the survival rates increasing because of improved detection and treatment, a more comprehensive understanding of the impact of current treatments on neurocognitive function and brain structure is critically needed. A frontline medulloblastoma clinical trial (SJMB03) has collected data, including treatment, clinical, neuroimaging, and cognitive variables. Advanced methods for modeling and integrating these data are critically needed to understand the mediation pathway from the treatment through brain structure to neurocognitive outcomes. We propose an integrative Bayesian mediation analysis approach to model jointly a treatment exposure, a high-dimensional structural neuroimaging mediator, and a neurocognitive outcome and to uncover the mediation pathway. The high-dimensional imaging-related coefficients are modeled via a binary Ising-Gaussian Markov random field prior (BI-GMRF), addressing the sparsity, spatial dependency, and smoothness and increasing the power to detect brain regions with mediation effects. Numerical simulations demonstrate the estimation accuracy, power, and robustness. For the SJMB03 study, the BI-GMRF method has identified white matter microstructure that is damaged by cancer-directed treatment and impacts late neurocognitive outcomes. The results provide guidance on improving treatment planning to minimize long-term cognitive sequela for pediatric brain tumor patients.

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.

White matter tract changes in pediatric posterior fossa brain tumor survivors after surgery and chemotherapy

BACKGROUND

Survivors of pediatric posterior fossa brain tumors are susceptible to the adverse effects of treatment as they grow into adulthood. While the exact neurobiological mechanisms of these outcomes are not yet understood, the effects of treatment on white matter (WM) tracts in the brain can be visualized using diffusion tensor (DT) imaging. We investigated these WM microstructural differences using the statistical method tract-specific analysis (TSA). We applied TSA to the DT images of 25 children with a history of posterior fossa tumor (15 treated with surgery, 10 treated with surgery and chemotherapy) along with 21 healthy controls. Between these 3 groups, we examined differences in the most used DTI metric, fractional anisotropy (FA), in 11 major brain WM tracts.

RESULTS

Lower FA was found in the splenium of the corpus callosum (CC), the bilateral corticospinal tract (CST), the right inferior frontal occipital fasciculus (IFOF) and the left uncinate fasciculus (UF) in children with brain tumors as compared to healthy controls. Lower FA, an indicator of microstructural damage to WM, was observed in 4 of the 11 WM tracts examined in both groups of children with a history of posterior fossa tumor, with an additional tract unique to children who received surgery and chemotherapy (left UF).

CONCLUSIONS

Our findings indicate that a history of tumor in the posterior fossa and surgical resection may have effects on the WM in other parts of the brain.

Toxicity and Clinical Results after Proton Therapy for Pediatric Medulloblastoma: A Multi-Centric Retrospective Study

Medulloblastoma is the most common malignant brain tumor in children. Even if current treatment dramatically improves the prognosis, survivors often develop long-term treatment-related sequelae. The current radiotherapy standard for medulloblastoma is craniospinal irradiation with a boost to the primary tumor site and to any metastatic sites. Proton therapy (PT) has similar efficacy compared to traditional photon-based radiotherapy but might achieve lower toxicity rates. We report on our multi-centric experience with 43 children with medulloblastoma (median age at diagnosis 8.7 years, IQR 6.6, M/F 23/20; 26 high-risk, 14 standard-risk, 3 ex-infant), who received active scanning PT between 2015 and 2021, with a focus on PT-related acute-subacute toxicity, as well as some preliminary data on late toxicity. Most acute toxicities were mild and manageable with supportive therapy. Hematological toxicity was limited, even among HR patients who underwent hematopoietic stem-cell transplantation before PT. Preliminary data on late sequelae were also encouraging, although a longer follow-up is needed.

A review of long-term deficits in memory systems following radiotherapy for pediatric posterior fossa tumor

INTRODUCTION

In recent years, progress in pediatric posterior fossa tumor (PFT) treatments has improved survival rates. However, the majority of survivors present neurocognitive sequelae that impact academic achievement.

METHODS

This review examines the literature from 2000 to 2020 on long-term outcomes in different memory systems for survivors of pediatric PFT, considering the impact of radiotherapy which is a well-known prognostic factor for global neurocognitive function.

RESULTS

Of the 43 articles selected, 31 explored working memory, 19 episodic memory, 9 semantic memory and 2 procedural memory. Irradiated survivors had scores of < -2 standard deviation (SD) (n = 4 studies/25) or between -2SD and -1SD (n =7 studies/25) for working memory; < -1SD for anterograde memory (n = 11/13), with a progressive decline in these two memory systems; < -1SD (n = 4/7) in semantic memory, and a deficit in perceptual-motor procedural learning (n = 1/1). Reducing craniospinal irradiation dose, limiting tumor bed boosts, and using proton therapy seem to have had a beneficial effect with better preservation of the memory score and a reduction in the decline over time. Non-irradiated survivors had memory systems that were less affected, with preservation of anterograde memory and maintenance of long-term stability.

CONCLUSION

Memory deficits are a core feature in survivors of pediatric PFT, especially when treatment requires radiotherapy. To limit these effects, dose constraints for specific brain areas involved in memory should be defined. During long-term follow-up, specific attention is essential to identify these deficits in order to limit their impact on the quality of life.

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.

Diffusion tensor imaging indices as biomarkers for cognitive changes following paediatric radiotherapy: a systematic review and meta-analysis

Diffusion tensor imaging (DTI) can detect subtle manifestations of white matter (WM) injury following paediatric radiotherapy, which may be a potential biomarker for cognitive changes. This study aimed to synthesise the relationships between DTI indices and cognitive changes following paediatric radiotherapy through systematic review and meta-analysis. PubMed and Scopus electronic databases were used to identify eligible studies. Quality assessment was performed using the National Institute of Health (NIH) Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. Information on demographics, DTI changes, and associations to cognitive outcomes were extracted. Meta-analyses were performed on DTI changes in specific anatomical locations. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed in the preparation of this report. Eighteen studies were included (median study size: 21; range 18-146). 17/18 studies showed significant cognitive decline following irradiation. Meta-analyses found significant cognitive changes within patient's group of acute lymphoblastic leukaemia (ALL; standard mean differences [SMD] = -0.075, P = 0.01) and brain tumours (BT; SMD = -1.037, P ≤ 0.001) compared to control/baseline. Both groups also had significantly lower fractional anisotropy (FA) scores in the corpus callosum (ALL: SMD = -0.979, P = 0.002; BT: SMD = -1.025, P < 0.001). Decreased FA was consistently associated with cognitive decline. Correlation on WMFA integrity to cognitive domains was statistically significant (Z = 9.86, P < 0.001) with a large effect size (r = 0.52). White matter tract integrity of the corpus callosum measured with FA has the potential to be a biomarker for radiotherapy-related cognitive decline. Inclusion of DTI in follow-up imaging should be encouraged.

Association Between Brain Substructure Dose and Cognitive Outcomes in Children With Medulloblastoma Treated on SJMB03: A Step Toward Substructure-Informed Planning

PURPOSE

To characterize the association between neurocognitive outcomes (memory and processing speed) and radiation (RT) dose to the hippocampus, corpus callosum (CC), and frontal white matter (WM) in children with medulloblastoma treated on a prospective study, SJMB03.

PATIENTS AND METHODS

Patients age 3-21 years with medulloblastoma were treated at a single institution on a phase III study. The craniospinal RT dose was 23.4 Gy for average-risk patients and 36-39.6 Gy for high-risk patients. The boost dose was 55.8 Gy to the tumor bed. Patients underwent cognitive testing at baseline and once yearly for 5 years. Performance on tests of memory (associative memory and working memory) and processing speed (composite processing speed and perceptual speed) was analyzed. Mixed-effects models were used to estimate longitudinal trends in neurocognitive outcomes. Reliable change index and logistic regression were used to define clinically meaningful neurocognitive decline and identify variables associated with decline.

RESULTS

One hundred and twenty-four patients were eligible for inclusion, with a median neurocognitive follow-up of 5 years. Mean right and left hippocampal doses were significantly associated with decline in associative memory in patients without posterior fossa syndrome (all P < .05). Mean CC and frontal WM doses were significantly associated with decline in both measures of processing speed (all P < .05). Median brain substructure dose-volume histograms were shifted to the right for patients with a decline in associative memory or processing speed. The odds of decline in associative memory and composite processing speed increased by 23%-26% and by 10%-15% for every 1-Gy increase in mean hippocampal dose and mean CC or frontal WM dose, respectively.

CONCLUSION

Increasing RT dose to the CC or frontal WM and hippocampus is associated with worse performance on tests of processing speed and associative memory, respectively. Brain substructure-informed RT planning may mitigate neurocognitive impairment.

Immunotherapy in Medulloblastoma: Current State of Research, Challenges, and Future Perspectives

Medulloblastoma (MB), a primary tumor of the central nervous system, is among the most prevalent pediatric neoplasms. The median age of diagnosis is six. Conventional therapies include surgical resection of the tumor with subsequent radiation and chemotherapy. However, these therapies often cause severe brain damage, and still, approximately 75% of pediatric patients relapse within a few years. Because the conventional therapies cause such severe damage, especially in the pediatric developing brain, there is an urgent need for better treatment strategies such as immunotherapy, which over the years has gained accumulating interest. Cancer immunotherapy aims to enhance the body's own immune response to tumors and is already widely used in the clinic, e.g., in the treatment of melanoma and lung cancer. However, little is known about the possible application of immunotherapy in brain cancer. In this review, we will provide an overview of the current consensus on MB classification and the state of in vitro, in vivo, and clinical research concerning immunotherapy in MB. Based on existing evidence, we will especially focus on immune checkpoint inhibition and CAR T-cell therapy. Additionally, we will discuss challenges associated with these immunotherapies and relevant strategies to overcome those.

White matter hyperintensity volumes are related to processing speed in long-term survivors of childhood cerebellar tumors

PURPOSE

Across several clinical populations, higher white matter hyperintensity (WMH) burden is consistently associated with decreases in cognitive performance, especially processing speed. Research of childhood cancer survivors has not utilized WMH quantification methodology to better understand the impact of WMH burden and its relationship with core cognitive skills. The present study aimed to quantify WMH volumes in a sample of long-term survivors of childhood cerebellar tumor and investigate the relationships with performance on a measure of oral processing speed. To further explore brain-behavior relationships, multivariate sparse canonical correlations was employed to identify WMH areas that predict processing speed performance.

METHODS

Thirty-five survivors and 56 healthy controls underwent neuroimaging and completed a measure of oral processing speed. The survivor group was further divided based on treatment (i.e., chemoradiation therapy (n = 20) vs. surgery only (n = 15)) to better understand the impact of treatment.

RESULTS

Survivors, and especially those treated with chemoradiation therapy, showed higher total WMH volumes and slower processing speed. Higher total WMH volumes were significantly associated with poorer processing speed (r = - 0.492, p = 0.003). Multivariate brain-behavior relationships revealed that periventricular WMHs were significantly associated with slower processing speed performance (p < 0.05).

CONCLUSION

Results exemplify that long-term survivors treated with and without chemoradiation therapy are at increased risk of developing higher WMH volumes compared to healthy peers. In addition, processing speed was robustly shown to be related to periventricular WMHs using an automated neuroimaging pipeline. This methodology to monitor WMH burden has the potential to be implemented efficiently with routine clinical neuroimaging of cancer survivors.

Assessing neuropsychological phenotypes of pediatric brain tumor survivors

INTRODUCTION

Pediatric brain tumor survivors (PBTS) are at risk for both neurocognitive impairments and psychological difficulties, yet these two domains have historically been discretely examined, with assessment of psychosocial outcomes rarely included in studies of cognitive outcomes. Taking a person-centered approach, the current study aimed to more comprehensively evaluate PBTS late effect profiles, including both neurocognitive and psychological sequelae, and predictors of these profiles.

METHOD

PBTS (N = 89) were assessed in a pediatric neuropsychological clinic between May 2009 and May 2018, diagnosed at least 1 year prior, and off-treatment for at least 3 months (M_age  = 6.57 years, SD = 4.53; 46.1% female). Parent- and teacher-report of psychological symptoms, and performance-based measures of neurocognitive functioning were examined using latent profile analysis. The R3STEP procedure identified predictors of class membership.

RESULTS

The optimal model identified four classes characterized by: (1) average functioning across all measures ("Average," n = 47), (2) average psychosocial functioning and impaired neurocognitive functioning ("Cognitive Deficit," n = 25), (3) elevated social problems and significant neurocognitive impairments ("Social/Cognitive Deficit," n = 9), and (4) impaired visual planning and problem-solving and elevated parent-reported psychosocial problems, but average processing speed, working memory, and teacher-reported psychosocial outcomes ("Discrepant," n = 8). Ethnicity, race, radiation treatment, and diagnoses of neurofibromatosis 1, hydrocephalus, and cerebellar mutism syndrome were significant predictors of class membership (ps < 0.05).

CONCLUSION

The present study identified distinct phenotypes with unique patterns of relations among neurocognitive and psychological domains. These findings are a vital first step toward identifying those at highest risk for poor outcomes and informing interventions that effectively address interrelated treatment targets for specific groups.

Early neuropsychological profile of children diagnosed with a brain tumor predicts later academic difficulties at school age

PURPOSE

Children diagnosed with a brain tumor (BT) in the first years of their life are at high risk of cognitive and neuropsychological problems, more school difficulties, and an increased need for educational support. To improve this condition, it will be beneficial to be able to identify the neuropsychological variables that are early predictors of school competences at later ages.

METHODS

We longitudinally assessed 30 school-age BT children with a diagnosis before the age of 5 who were administered cognitive and neuropsychological evaluations before entering school or in the first 2 school years and who were followed up for academic performance at least one year after the first evaluation. A discriminant function analysis was conducted to detect the early neuropsychological profile that best predicted those children who turned out to need school support or not; we tested 5 block multiple regression models, one for each academic variable entering as predictors the neuropsychological variables that significantly discriminated the two groups.

RESULTS

A total of 93.3% of the cases were correctly classified according to the discriminant function in "with vs. without" educational support. Visual attention abilities were highly correlated with resulting school problems, both for reading (accuracy and speed) and math (operations) at school age.

CONCLUSIONS

Analysis provided evidence that the early neuropsychological profile may predict academic difficulties for both reading and math at school age and that visual attention seems to play an important role in both these academic abilities, allowing clinicians to identify children with major difficulties in/from early years and to intervene beforehand.

Diffusion Tensor Imaging-Based Analysis of Baseline Neurocognitive Function and Posttreatment White Matter Changes in Pediatric Patients With Craniopharyngioma Treated With Surgery and Proton Therapy

PURPOSE

To determine the preirradiation baseline association of white matter integrity with neurocognitive function and to assess posttreatment changes in pediatric patients with craniopharyngioma treated with proton therapy.

METHODS AND MATERIALS

Ninety children and adolescents (2-20 years old) with craniopharyngioma were treated with proton therapy (54 Gy[RBE]) in a prospective therapeutic trial. Neurocognitive performance at the postoperative baseline before proton therapy and diffusion tensor imaging (DTI) data acquired at baseline and at annual follow-up were analyzed. Tract-based spatial statistics and structural connectomics were used to derive global and local white matter features from DTI. Baseline DTI features were compared for patients with average and below-average neurocognitive performance. Longitudinal DTI data were analyzed to determine the proton dose effect on white matter structures in relation to the irradiated brain volume and baseline age.

RESULTS

Before proton therapy, patients with below-average working memory, processing speed, verbal fluency, verbal learning, or fine motor dexterity exhibited more globally degraded white matter structures compared with their counterparts with average performance, as indicated by lower mean fractional anisotropy, decreased global efficiency, or higher modularity. Surgery, obstructive hydrocephalus, and preoperative hypothalamic involvement appeared to be related to this degradation. In local analyses, tract-based spatial statistics revealed left-lateralized associations with verbal and motor functions, which supported surgical approaches to midline tumors via the right hemisphere. The mean fractional anisotropy of the brain and the global efficiency derived from DTI increased over the 5 years after proton therapy. The rate of increase was lower with larger irradiated brain volumes and in older children.

CONCLUSIONS

Below-average baseline neurocognitive performance in patients with craniopharyngioma before proton therapy appeared to be related to structural degradation of white matter tracts. Posttherapy longitudinal DTI showed improving trends in global integrity and efficiency measures, particularly in children in whom a smaller brain volume was irradiated.

Cerebellar-Subcortical-Cortical Systems as Modulators of Cognitive Functions

Over the past few decades, research has established that the cerebellum is involved in executive functions; however, its specific role remains unclear. There are numerous theories of cerebellar function and numerous cognitive processes falling under the umbrella of executive function, making investigations of the cerebellum's role in executive functioning challenging. In this review, we explored the role of the cerebellum in executive functioning through clinical and cognitive neuroscience frameworks. We reviewed the neuroanatomical systems and theoretical models of cerebellar functions and the multifaceted nature of executive functions. Using attention deficit hyperactivity disorder and cerebellar tumor as clinical developmental models of cerebellar dysfunction, and the functional magnetic resonance imaging literature, we reviewed evidence for cerebellar involvement in specific components of executive function in childhood, adolescence, and adulthood. There is evidence for posterior cerebellar contributions to working memory, planning, inhibition, and flexibility, but the heterogeneous literature that largely was not designed to study the cerebellum makes it difficult to determine specific functions of the cerebellum or cerebellar regions. In addition, while it is clear that cerebellar insult in childhood affects executive function performance later in life, more work is needed to elucidate the mechanisms by which executive dysfunction occurs and its developmental course. The limitations of the current literature are discussed and potential directions for future research are provided.

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.

Neuropsychological functioning in survivors of childhood medulloblastoma/CNS-PNET: The role of secondary medical complications

OBJECTIVE

To investigate the long-term cognitive consequences of malignant pediatric brain tumor and its treatment, and factors explaining variability in cognitive functioning among survivors. Method: A geographical cohort of survivors of pediatric medulloblastoma (MB) and supratentorial primitive neuroectodermal tumor (CNS-PNET), treated between 1974 and 2013, was invited to participate. Of the 63 surviving patients, 50 (79%) consented to participation. The participants were tested with a battery of neuropsychological tests covering a wide age range. Verbal cognition, nonverbal cognition, processing speed, attention, memory, executive functioning, and manual dexterity were assessed. The participants were between 5:5 and 51:11 years of age at time of assessment. Assessments took place on average 19 years after primary tumor resective surgery. Results: One participant had a severe intellectual disability. For the rest, IQ varied from 52 to 125, with a mean score of 88.0 (SD 19.7). Twenty-eight (56%) of the participants had full-scale IQ scores in the age-average range or above. Gender, age at operation, time since operation, the presence of secondary medical complications, and treatment variables explained 46% of the variability in IQ scores, F(4,44) =  9.5, p<.001. The presence of endocrine insufficiency in combination with either epilepsy and/or hydrocephalus was associated with lowered IQ, lowered processing speed, and memory impairments. Conclusion: Patients treated for childhood MB and CNS-PNET have a lifelong risk of medical sequelae, including impaired cognitive functioning. This study adds to the literature by demonstrating the importance of following neuropsychological functioning closely, especially processing speed, learning, and memory, in survivors who have multiple secondary medical complications.

Late effects of pediatric brain tumors

PURPOSE OF REVIEW

Adverse late effects of pediatric brain tumors can be numerous and complex and potentially alter the life trajectories of survivors in a multitude of ways. We review these inter-related late effects that compromise neurocognitive function, general health, social and psychological adjustment, and overall adaptive and vocational outcomes, and threaten to undermine the ability of survivors to transition independently into adulthood and effectively manage their care. Intervention/prevention strategies and advances in treatment that may reduce such late effects are discussed.

RECENT FINDINGS

Studies of neuropsychological late effects have revealed specific deficits in core cognitive functions of attention, working memory and processing speed, with many survivors demonstrating decline in working memory and processing speed over time, irrespective of tumor type or treatment. This in turn affects the ongoing development of higher order neurocognitive skills. Research also highlights the increasing burden of health-related, neuropsychological and psychosocial late effects into adulthood and impact across life outcomes.

SUMMARY

Pediatric brain tumor survivors require coordinated interdisciplinary care, ongoing evaluation and management of late effects, and timely interventions focused on mitigating the impact of late effects. The transition to adulthood can be especially vulnerable and addressing barriers to care is of paramount importance.

A comprehensive preclinical assessment of late-term imaging markers of radiation-induced brain injury

Background

Cranial radiotherapy (CRT) is an important part of brain tumor treatment, and although highly effective, survivors suffer from long-term cognitive side effects. In this study we aim to establish late-term imaging markers of CRT-induced brain injury and identify functional markers indicative of cognitive performance. Specifically, we aim to identify changes in executive function, brain metabolism, and neuronal organization.

Methods

Male Sprague Dawley rats were fractionally irradiated at 28 days of age to a total dose of 30 Gy to establish a radiation-induced brain injury model. Animals were trained at 3 months after CRT using the 5-choice serial reaction time task. At 12 months after CRT, animals were evaluated for cognitive and imaging changes, which included positron emission tomography (PET) and magnetic resonance imaging (MRI).

Results

Cognitive deficit with signs of neuroinflammation were found at 12 months after CRT in irradiated animals. CRT resulted in significant volumetric changes in 38% of brain regions as well as overall decrease in brain volume and reduced gray matter volume. PET imaging showed higher brain glucose uptake in CRT animals. Using MRI, irradiated brains had an overall decrease in fractional anisotropy, lower global efficiency, increased transitivity, and altered regional connectivity. Cognitive measurements were found to be significantly correlated with six image features that included myelin integrity and local organization of the neural network.

Conclusions

These results demonstrate that CRT leads to late-term morphological changes, reorganization of neural connections, and metabolic dysfunction. The correlation between imaging markers and cognitive deficits can be used to assess late-term side effects of brain tumor treatment and evaluate efficacy of new interventions.

Neuroimaging of the component white matter connections and structures within the cerebellar-frontal pathway in posterior fossa tumor survivors

Introduction

In posterior fossa tumor survivors, lower white matter integrity (WMI) in the right cerebellar-left frontal pathway has been well documented and appears to be related to proximity to the cerebellum, radiation treatment, as well as time since treatment in both cranial radiation and surgery-only treatment groups. The current study investigated theories of transneural degeneration following cerebellar tumor resection that may underlie or relate to reductions in WMI and regional brain volumes using correlations. We hypothesized a positive relationship between the volume of the right cerebellum and known white matter output pathways, as well as with the volume of structures that receive cerebellar projections along the pathway.

Methods

Adult survivors of childhood brain tumors were recruited (n = 29; age, M = 22 years, SD = 5; 45% female). Age- and gender-matched controls were also included (n = 29). Participants completed 3 T diffusion-weighted and T1 MPRAGE MRI scans. Brain structure volume relative to intracranial vault served as regional volumetric measures. Fractional anisotropy (FA) and radial diffusivity (RD) served as WMI measures. In the survivor group, partial correlations between WMI and regional volume included controlling for disease severity.

Results

In posterior fossa tumor survivors, the volumes of the cerebellum, thalamus, and frontal lobe were correlated with WMI of the thalamic-frontal segment of the cerebellar-frontal pathway (r = 0.41–0.49, p < .05). Cerebellar atrophy was correlated with reduced WMI in the cerebellar-rubral segment (FA, r = −0.32 p > .05; RD, r = 0.53, p < .01). In the no-radiation survivor group, the regional volume of each structure along the pathway was associated with WMI in the cerebellar-rubral segment. In the radiation survivor group, significant correlations were found between the regional brain volume of each structure and the thalamic-frontal segment of the pathway.

Discussion

The results of this multimodal neuroimaging study provide correlational evidence that the mechanism of injury subsequent to brain tumor treatment may be different depending on type of treatment(s). Without radiation, the primary mechanism of injury is cerebellar tumor growth, resection, and hydrocephalus. Therefore, the most proximal connection to that injury (cerebellar-rubral pathway) was correlated with reductions in volume along the pathway. In contrast, the survivor group treated with radiation may have had possible radiation-induced demyelination of the thalamic-frontal portion of the pathway, based on a strong correlation with volume loss in the cerebellum, red nucleus, thalamus, and frontal lobe.

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Cerebellar atrophy predicted lower white matter integrity (WMI) in the cerebellar-rubral segment.

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The no-radiation group showed a correlational pattern that is consistent with possible transneural degeneration.

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The radiation group showed a correlational pattern consistent with theories of neurodevelopmental vulnerability to radiation-induced demyelination.

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.

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