Unidentified bright objects in neurofibromatosis type 1: conventional MRI in the follow-up and correlation of microstructural lesions on diffusion tensor images

Evaluating Focal Areas of Signal Intensity (FASI) in Children with Neurofibromatosis Type-1 (NF1) Treated with Selumetinib on Pediatric Brain Tumor Consortium (PBTC)-029B

Background: Understanding the effect of selumetinib on FASI may help elucidate the biology, proliferative potential, and role in neurocognitive changes for these NF1-associated lesions. Methods: Patients with NF1-associated LGG and FASI treated with selumetinib on PBTC-029B were age-matched to untreated patients with NF1-associated FASI at Cincinnati Children’s Hospital Medical Center. Paired bidirectional measurements were compared over time using nonparametric tests. Results: Sixteen age-matched pairs were assessed (age range: 2.8–16.9 years, 60% male). Initial FASI burden was not different between groups (median range 138.7 cm2 [88.4–182.0] for the treated subjects vs. 121.6 cm2 [79.6—181.9] for the untreated subjects; p = 0.98). Over a mean follow-up of 18.9 (±5.9) months, the LGG size consistently decreased with treatment while no consistent change among the treated or untreated FASI size was seen. At the paired time points, the median treated LGG decreased significantly more than the treated FASI (−41.3% (LGG) versus −10.7% (FASI), p = 0.006). However, there was no difference in the median size change in the treated versus untreated FASI (−10.7% (treated FASI) versus −17.9% (untreated FASI), p = 0.08). Among the treated subjects, there was no correlation between the change in LGG and FASI (r = −0.04, p = 0.88). Conclusions: Treatment with selumetinib did not affect the overall FASI size in children with NF1 treated for progressive low-grade glioma.

Neurofibromatosis Type 1: Pediatric Aspects and Review of Genotype-Phenotype Correlations

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition, with a birth incidence of approximately 1:2000-3000, caused by germline pathogenic variants in NF1, a tumor suppressor gene encoding neurofibromin, a negative regulator of the RAS/MAPK pathway. This explains why NF1 is included in the group of RASopathies and shares several clinical features with Noonan syndrome. Here, we describe the main clinical characteristics and complications associated with NF1, particularly those occurring in pediatric age. NF1 has complete penetrance and shows wide inter- and intrafamilial phenotypic variability and age-dependent appearance of manifestations. Clinical presentation and history of NF1 are multisystemic and highly unpredictable, especially in the first years of life when penetrance is still incomplete. In this scenario of extreme phenotypic variability, some genotype-phenotype associations need to be taken into consideration, as they strongly impact on genetic counseling and prognostication of the disease. We provide a synthetic review, based on the most recent literature data, of all known genotype-phenotype correlations from a genetic and clinical perspective. Molecular diagnosis is fundamental for the confirmation of doubtful clinical diagnoses, especially in the light of recently revised diagnostic criteria, and for the early identification of genotypes, albeit few, that correlate with specific phenotypes.

Presence of neurologic signs in children with neurofibromatosis type 1

BACKGROUND

Neurofibromatosis type 1 is a common neurogenetic disorder affecting nervous system, caused by germiline mutations of the NF1 gene. Although the clinical diagnosis of NF1 is defined by presence of cafe-au-laits spots, freckling and benign tumors (neurofibromatosis), neurocognitive impairment and neuropsychiatric disorders are reported in comorbidity. Children with NF1 show higher incidence of executive deficits, such attention, response inhibition, executive planning and problem solving, working memory, and learning impairment. In this study we examine the presence of neurological soft signs and planning function in subjects with NF1. The NSS are minor motor and sensory abnormalities without focal brain damage.

METHODS

Eleven drug naïve children between 7-15 years with clinical and molecular diagnosis of NF are matched to 11 healthy controls to ass the presence of neurological soft signs and planning executive functions. NSS were assessed using Physical and Neurological Examination for Subtle Signs and the Tower of London task is performance test to assess the capacity of planning, organization and execution of a work.

RESULTS

Our results revealed highest rate of NSS and planning deficit in children with NF1 compared to healthy controls.

CONCLUSIONS

The motor abnormalities and planning deficit are possible markers to confirm that NF1 could be considering a neurodevelopmental disorder.

Non-Oncological Neuroradiological Manifestations in NF1 and Their Clinical Implications

Simple Summary

Central nervous system involvement (CNS) is a common finding in Neurofibromatosis type 1 (NF1). Beside tumor-related manifestations, NF1 is also characterized by a wide spectrum of CNS alterations with variable impacts on functioning and life quality. Here, we propose an overview of non-oncological neuroradiological findings in NF1, with an insight on pathophysiological and embryological clues for a better understanding of the development of these specific alterations.

Abstract

Neurofibromatosis type 1 (NF1), the most frequent phakomatosis and one of the most common inherited tumor predisposition syndromes, is characterized by several manifestations that pervasively involve central and peripheral nervous system structures. The disorder is due to mutations in the NF1 gene, which encodes for the ubiquitous tumor suppressor protein neurofibromin; neurofibromin is highly expressed in neural crest derived tissues, where it plays a crucial role in regulating cell proliferation, differentiation, and structural organization. This review article aims to provide an overview on NF1 non-neoplastic manifestations of neuroradiological interest, involving both the central nervous system and spine. We also briefly review the most recent MRI functional findings in NF1.

Focal Areas of High Signal Intensity in Children with Neurofibromatosis Type 1: Expected Evolution on MRI

BACKGROUND AND PURPOSE

Focal areas of high signal intensity are T2WI/T2-FLAIR hyperintensities frequently found on MR imaging of children diagnosed with neurofibromatosis type 1, often thought to regress spontaneously during adolescence or puberty. Due to the risk of tumor in this population, some focal areas of high signal intensity may pose diagnostic problems. The objective of this study was to assess the characteristics and temporal evolution of focal areas of high signal intensity in children with neurofibromatosis type 1 using long-term follow-up with MR imaging.

MATERIALS AND METHODS

We retrospectively examined the MRIs of children diagnosed with neurofibromatosis type 1 using the National Institutes of Health Consensus Criteria (1987), with imaging follow-up of at least 4 years. We recorded the number, size, and surface area of focal areas of high signal intensity according to their anatomic distribution on T2WI/T2-FLAIR sequences. A generalized mixed model was used to analyze the evolution of focal areas of high signal intensity according to age, and separate analyses were performed for girls and boys.

RESULTS

Thirty-nine patients (ie, 285 MR images) with a median follow-up of 7 years were analyzed. Focal areas of high signal intensity were found in 100% of patients, preferentially in the infratentorial white matter (35% cerebellum, 30% brain stem) and in the capsular lenticular region (22%). They measured 15 mm in 95% of cases. They appeared from the age of 1 year; increased in number, size, and surface area to a peak at the age of 7; and then spontaneously regressed by 17 years of age, similarly in girls and boys.

CONCLUSIONS

Focal areas of high signal intensity are mostly small (<15 mm) abnormalities in the posterior fossa or capsular lenticular region. Our results suggest that the evolution of focal areas of high signal intensity is not related to puberty with a peak at the age of 7 years. Knowledge of the predictive evolution of focal areas of high signal intensity is essential in the follow-up of children with neurofibromatosis type 1.

Response assessment in paediatric low-grade glioma: recommendations from the Response Assessment in Pediatric Neuro-Oncology (RAPNO) working group

Paediatric low-grade gliomas (also known as pLGG) are the most common type of CNS tumours in children. In general, paediatric low-grade gliomas show clinical and biological features that are distinct from adult low-grade gliomas, and the developing paediatric brain is more susceptible to toxic late effects of the tumour and its treatment. Therefore, response assessment in children requires additional considerations compared with the adult Response Assessment in Neuro-Oncology criteria. There are no standardised response criteria in paediatric clinical trials, which makes it more difficult to compare responses across studies. The Response Assessment in Pediatric Neuro-Oncology working group, consisting of an international panel of paediatric and adult neuro-oncologists, clinicians, radiologists, radiation oncologists, and neurosurgeons, was established to address issues and unique challenges in assessing response in children with CNS tumours. We established a subcommittee to develop consensus recommendations for response assessment in paediatric low-grade gliomas. Final recommendations were based on literature review, current practice, and expert opinion of working group members. Consensus recommendations include imaging response assessments, with additional guidelines for visual functional outcomes in patients with optic pathway tumours. As with previous consensus recommendations, these recommendations will need to be validated in prospective clinical trials.

Effect of age and neurofibromatosis type 1 status on white matter integrity in the optic radiations

Background

Adults with neurofibromatosis type 1 (NF1) have decreased white matter integrity, but differences in children with NF1 have not been described. Defining normal values for diffusion tensor imaging (DTI) measures, especially in the optic radiations, is important to the development of DTI as a potential biomarker of visual acuity in children with optic pathway glioma. This study examines the effect of age and NF1 status on DTI measures in children.

Methods

In this retrospective study, MR imaging including DTI was conducted in 93 children (40 children with NF1 and 53 healthy controls) between 0 and 14 years of age. Regression models of age, sex, and NF1 status on DTI measures were evaluated, and tract-based spatial statistics (TBSS) compared DTI measures in age-matched NF1 to non-NF1 cohorts.

Results

Fractional anisotropy, radial diffusivity, and mean diffusivity in white matter tracts of the optic radiations varied with age and were best modeled by a logarithmic function. Age-related DTI measure change was different in NF1 versus non-NF1 subjects. Normal values and 95% confidence intervals for age 0.5–12 years were derived for both groups. Differences in DTI measures between NF1 and non-NF1 groups at a range of ages were shown diffusely throughout the cerebral white matter using TBSS.

Conclusions

Children with NF1 demonstrate increased diffusion throughout the brain compared to children without NF1 suggesting a potentially altered developmental trajectory of optic radiation microstructure. Defining normal values for white matter integrity in children with NF1 may help target early intervention efforts in this vulnerable group.

Can the Cognitive Phenotype in Neurofibromatosis Type 1 (NF1) Be Explained by Neuroimaging? A Review

Neurofibromatosis type 1 (NF1) is one of the most frequent monogenetic disorders. It can be associated with cognitive dysfunctions in several domains such as executive functioning, language, visual perception, motor skills, social skills, memory and/or attention. Neuroimaging is becoming more and more important for a clearer understanding of the neural basis of these deficits. In recent years, several studies have used different imaging techniques to examine structural, morphological and functional alterations in NF1 disease. They have shown that NF1 patients have specific brain characteristics such as Unidentified Bright Objects (UBOs), macrocephaly, a higher volume of subcortical structures, microstructure integrity alterations, or connectivity alterations. In this review, which focuses on the studies published after the last 2 reviews of this topic (in 2010 and 2011), we report on recent structural, morphological and functional neuroimaging studies in NF1 subjects, with special focus on those that examine the neural basis of the NF1 cognitive phenotype. Although UBOs are one of the most obvious and visible elements in brain imaging, correlation studies have failed to establish a robust and reproducible link between major cognitive deficits in NF1 and their presence, number or localization. In the same vein, the results among structural studies are not consistent. Functional magnetic resonance imaging (fMRI) studies appear to be more sensitive, especially for understanding the executive function deficit that seems to be associated with a dysfunction in the right inferior frontal areas and the middle frontal areas. Similarly, fMRI studies have found that visuospatial deficits could be associated with a dysfunction in the visual cortex and especially in the magnocellular pathway involved in the processing of low spatial frequency and high temporal frequency. Connectivity studies have shown a reduction in anterior-posterior “long-range” connectivity and a deficit in deactivation in default mode network (DMN) during cognitive tasks. In conclusion, despite the contribution of new imaging techniques and despite relative advancement, the cognitive phenotype of NF1 patients is not totally understood.

Discriminating between neurofibromatosis-1 and typically developing children by means of multimodal MRI and multivariate analyses

Neurofibromatosis Type 1 leads to brain anomalies involving both gray and white matter. The extent and granularity of these anomalies, together with their possible impact on brain activity, is still unknown. In this multicentric cross-sectional study we submitted a sample of 42 typically developing and 38 neurofibromatosis-1 children to a multimodal MRI assessment including T1, diffusion weighted and resting state functional sequences. We used a pipeline involving several features selection steps coupled with multivariate statistical analysis (supporting vector machine) to discriminate between the two groups while having interpretable models. We used MRI indexes measuring macro (gray matter volume) and microstructural (fractional anisotropy, mean diffusivity) characteristics of the brain, as well as indexes of brain activity (fractional amplitude of low frequency fluctuations) and connectivity (local and global correlation) at rest. We found that structural indexes could discriminate between the two groups, with the mean diffusivity leading to performance as high as the combination of all structural indexes combined (accuracy = 0.86), while functional indexes had worse performances. The MRI signature of NF1 brain pathology is a combination of gray and white matter abnormalities, as measured with gray matter volume, fractional anisotropy, and mean diffusivity.

Cerebellar radiological abnormalities in children with neurofibromatosis type 1: part 1 - clinical and neuroimaging findings

Background

Many children with neurofibromatosis type 1 (NF1) have focal abnormal signal intensities (FASI) on brain MRI, whose full clinical impact and natural history have not been studied systematically. Our aims are to describe the clinical and neuroradiological features in children with NF1 and cerebellar FASI, and report on the natural history of FASI that display atypical features such as enhancement and mass effect.

Method

A retrospective review of the hospital charts and brain MRIs was performed on children from Manitoba diagnosed between 1999 and 2008 with NF1, who also had cerebellar FASI on MRI.

Results

Fifty patients (mean age: 16.1y, minimum-maximum: 6.4 - 30y, 27 M) were identified. Mean duration of follow up was 10.1y. Developmental delay, learning disabilities, tumors, and visual signs occurred commonly. Cerebellar signs were not reported. Mean age of the patients at baseline MRI was 7.8 (SD: 4.5) years. FASI occurred in several brain locations and were rarely confined to the cerebellum. FASI displayed mass effect and enhancement infrequently but were associated with malignancy only once. The number of FASI at baseline MRI was significantly less in patients with attention deficient hyperactivity disorder and more if a first degree relative had NF1 or if they had decreased visual acuity.

Discussion

Patients with NF1 and cerebellar FASI do not have motor or consistent non-motor (e.g. developmental delay or learning disabilities) cerebellar features. The number of FASI may correlate with some clinical features. FASI may display enhancement and mass effect but they rarely become malignant.

Cerebellar radiological abnormalities in children with neurofibromatosis type 1: part 2 - a neuroimaging natural history study with clinical correlations

Background

Focal abnormal signal intensities (FASI) on brain MRI occur commonly in patients with neurofibromatosis type 1 (NF1). The natural history of cerebellar FASI and their correlation with clinical features have not been studied comprehensively. Our aims are to describe the natural history of cerebellar FASI on repeat MRI scans and correlate the findings with the clinical features in children with NF1 and cerebellar FASI.

Method

A retrospective review of 226 brain MRI scans and hospital charts was performed in 50 patients with cerebellar FASI, who were diagnosed with NF1 during their childhood between 1999 and 2008.

Results

Mean age at the end of the study period was 16.1 years. There were 27 males. Mean duration of clinical follow up was 10.1 years. Mean duration between the first and the last MRI was 6.6 years (n = 36, SD: 2.8 years). FASI were rarely confined to the cerebellum. The number of FASI was highest in early childhood and decreased significantly on subsequent MRI scans in most brain regions with the exception of the cerebrum, where a fewer number of patients with a smaller number of FASI were seen. Four patterns of change in FASI size over time were determined, none correlated with the clinical features.

Conclusions

In patients with NF1, the natural history of FASI including their number, age at onset, rate of size changes, and resolution if any, varies by brain region. FASI patterns of change over time showed no clinical correlate.

A porcine model of neurofibromatosis type 1 that mimics the human disease

Loss of the NF1 tumor suppressor gene causes the autosomal dominant condition, neurofibromatosis type 1 (NF1). Children and adults with NF1 suffer from pathologies including benign and malignant tumors to cognitive deficits, seizures, growth abnormalities, and peripheral neuropathies. NF1 encodes neurofibromin, a Ras-GTPase activating protein, and NF1 mutations result in hyperactivated Ras signaling in patients. Existing NF1 mutant mice mimic individual aspects of NF1, but none comprehensively models the disease. We describe a potentially novel Yucatan miniswine model bearing a heterozygotic mutation in NF1 (exon 42 deletion) orthologous to a mutation found in NF1 patients. NF1+/ex42del miniswine phenocopy the wide range of manifestations seen in NF1 patients, including café au lait spots, neurofibromas, axillary freckling, and neurological defects in learning and memory. Molecular analyses verified reduced neurofibromin expression in swine NF1+/ex42del fibroblasts, as well as hyperactivation of Ras, as measured by increased expression of its downstream effectors, phosphorylated ERK1/2, SIAH, and the checkpoint regulators p53 and p21. Consistent with altered pain signaling in NF1, dysregulation of calcium and sodium channels was observed in dorsal root ganglia expressing mutant NF1. Thus, these NF1+/ex42del miniswine recapitulate the disease and provide a unique, much-needed tool to advance the study and treatment of NF1.

Serial MRIs provide novel insight into natural history of optic pathway gliomas in patients with neurofibromatosis 1

BACKGROUND

Optic pathway gliomas (OPGs) are present in 20% of children with neurofibromatosis 1 (NF1) but are less frequently observed in adults. Our goal was to determine the natural history of OPGs in children and adults with NF1.

RESULTS

We analyzed the features of OPGs and other intracranial lesions on 1775 head MRI scans of 562 unselected adults and children with NF1 collected between 2003 and 2015. 52 (9.3%) of 562 patients in this study had an OPG diagnosed on their MRI. The median age at first scan with an OPG present was 12.7 years. Of the 52 OPG patients, the intraorbital optic nerves were affected in 29 patients (56%), the prechiasmatic optic nerves were affected in 32 patients (62%), the optic chiasm was affected in 17 patients (33%) and the optic radiations were affected in 19 patients (37%). 29 patients had two or more areas affected. One patient had a newly-appearing OPG, and 1 patient showed progression. The rate of progression over 5 years was 2.4% (95% CI: 0.4% to 16%). Four patients showed partial regression of their OPGs, but we observed no case of complete regression during this study. The rate of regression over 5 years was 8.9% (95% confidence intervals: 2.8% to 26%). We found the presence of UBOs and the presence of OPGs in individual patients to be highly associated (p = 0.0061).

CONCLUSION

OPGs are more common in older adults with NF1 than previously thought. The occurrences of unidentified bright objects (UBOs) and asymptomatic OPGs are associated with each other. This suggests the possibility that OPGs that remain asymptomatic may differ pathogenically from those that become symptomatic.

Cancer and Central Nervous System Tumor Surveillance in Pediatric Neurofibromatosis 1

Although the neurofibromatoses consist of at least three autosomal dominantly inherited disorders, neurofibromatosis 1 (NF1), neurofibromatosis 2 (NF2), and schwannomatosis, NF1 represents a multisystem pleiotropic condition very different from the other two. NF1 is a genetic syndrome first manifesting in childhood; affecting multiple organs, childhood development, and neurocognitive status; and presenting the clinician with often complex management decisions that require a multidisciplinary approach. Molecular genetic testing (see article for detailed discussion) is recommended to confirm NF1, particularly in children fulfilling only pigmentary features of the diagnostic criteria. Although cancer risk is not the major issue facing an individual with NF1 during childhood, the condition causes significantly increased malignancy risks compared with the general population. Specifically, NF1 is associated with highly elevated risks of juvenile myelomonocytic leukemia, rhabdomyosarcoma, and malignant peripheral nerve sheath tumor as well as substantial risks of noninvasive pilocytic astrocytoma, particularly optic pathway glioma (OPG), which represent a major management issue. Until 8 years of age, clinical assessment for OPG is advised every 6 to 12 months, but routine MRI assessment is not currently advised in asymptomatic individuals with NF1 and no signs of clinical visual pathway disturbance. Routine surveillance for other malignancies is not recommended, but clinicians and parents should be aware of the small risks (<1%) of certain specific individual malignancies (e.g., rhabdomyosarcoma). Tumors do contribute to both morbidity and mortality, especially later in life. A single whole-body MRI should be considered at transition to adulthood to assist in determining approaches to long-term follow-up. Clin Cancer Res; 23(12); e46-e53. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

Unidentified Bright Objects on Brain Magnetic Resonance Imaging Affect Vestibular Neuritis

Objectives

The aim of this study was to investigate the differences in clinical manifestations of in two groups of vestibular neuritis (VN) patients with or without unidentified bright objects (UBOs).

Methods

A prospective, observational study with 46 patients diagnosed with VN between May 2013 and November 2013 was executed. A caloric test, a cervical vestibular-evoked myogenic potentials (cVEMPs) test, brain magnetic resonance imaging (MRI), spontaneous nystagmus test, head impulse test, and head-shaking nystagmus test were performed.

Results

Of the patients, 56.5% (n=26) were classified as UBO-positive by MRI. These showed lower caloric weakness and more prominent cVEMP asymmetry compared with the UBO-negative group (P<0.05). Total VN (TVN) was the most common in the UBO-positive group (45.0%), followed by superior VN (SVN, 30.0%), and inferior VN (IVN, 25.0%). However, in the UBO-negative group, SVN (75.0%) was the most common, followed by TVN and IVN (P<0.05). The recovery rate was not influenced by UBOs (P>0.05).

Conclusion

UBOs on T2-weighted or fluid attenuated inversion recovery MRI may affect the patterns of the vestibular nerve in patients with VN.

Functional Connectivity Changes and Executive and Social Problems in Neurofibromatosis Type I

Neurofibromatosis type 1 (NF1) has regularly been associated with cognitive, social, and behavioral problems. The fact that many different cognitive and behavioral impairments have been observed in NF1 suggests that networks of brain regions are involved rather than specific brain regions. Here, we examined whether functional connectivity was different in NF1 and, if so, whether associations were present with cognitive, social, and behavioral outcomes. Fourteen NF1 patients (8 male, age: M=12.49, SD=2.65) and 30 healthy controls (HC; 23 male, age: M=12.30, SD=2.94; p=0.835) were included. Functional connectivity was assessed using functional resting-state scanning. We analyzed brain regions that have been associated with cognitive and social functions: the bilateral ventral anterior cingulate cortex (vACC), the bilateral amygdala, the bilateral orbitofrontal cortex (OFC), and the posterior cingulate cortex (PCC). For NF1 patients, connection strengths between brain regions showing HC-NF1 differences were correlated with parent reports of cognitive, social, and behavioral functioning. Compared to HC, patients showed differences in functional connectivity between the left vACC and the frontal cortex, insula, and subcortical areas (caudate, putamen), between the left amygdala and the frontal cortex, insula, supramarginal gyrus, and PCC/precuneus, and between the left OFC and frontal and subcortical areas (caudate, pallidum). In patients, indications were found for associations between increased frontofrontal and temporofrontal functional connectivity with cognitive, social, and behavioral deficits (r-range=0.536-0.851). NF1 patients showed differences in functional connectivity between areas associated with cognitive and social functioning when compared to controls. This, plus the fact that connectivity strengths in these networks were associated with worse cognitive, social, and behavioral outcomes, suggests a neuropathological basis for the widespread deficits observed in NF1.

Is magnetic resonance spectroscopy capable of detecting metabolic abnormalities in neurofibromatosis type 1 that are not revealed in brain parenchyma of normal appearance?

BACKGROUND

Results of magnetic resonance spectroscopy studies in normal-appearing brain and in non-neoplastic brain lesions in individuals with neurofibromatosis type 1 (NF1) have been discrepant.

OBJECTIVE

We used magnetic resonance spectroscopy to analyze the metabolic patterns in the basal ganglia of patients with NF1 and examine their correlation with focal hyperintense lesions in T2-weighted images (T2-weighted hyperintensities).

METHODS

We used magnetic resonance spectroscopy data of 42 individuals with NF1 (18 with and 24 without T2- weighted hyperintensities) and 25 controls matched for gender and age. A single-voxel technique was employed by manually placing a region of interest with a uniform size over a predetermined anatomical region including the globus pallidum and putamen (capsulolenticular region). We further analyzed the ratios of choline/creatine, N-acetyl aspartate (NAA)/creatine, and myoinositol/creatine metabolites and the occurrence of T2-weighted hyperintensities in these regions in individuals with NF1.

RESULTS

There was a significant difference between the NF1 and control groups with regard to the mean values of myoinositol/creatine and choline/creatine, with higher metabolite values observed in the NF1 group (P < 0.001). Only the myoinositol/creatine ratio was able to discriminate between NF1 subgroups with and without T2-weighted hyperintensities. For the NAA/creatine ratio, there was no significant difference between the NF1 and the control groups.

CONCLUSION

Magnetic resonance spectroscopy allows the characterization of tissue abnormalities not demonstrable in the structural images of individuals with NF1 through choline and myoinositol metabolite analysis. Yet the preserved NAA values argue against demyelination and axonal degeneration occurring in the region, suggesting instead a functional neuronal stability. Taken in association with the findings of lack of clinical manifestations and the known transient nature of T2-weighted hyperintensities in NF1 as demonstrated by other studies, our results support the current histopathologically driven hypothesis that such T2-weighted hyperintensities may be related to intramyelinic edema.

Planning deficit in children with neurofibromatosis type 1: a neurocognitive trait independent from attention-deficit hyperactivity disorder (ADHD)?

Neurofibromatosis type 1 is associated with executive dysfunctions and comorbidity with attention-deficit hyperactivity disorder (ADHD) in 30% to 50% of children. This study was designed to clarify the neurocognitive phenotype observed in neurofibromatosis type 1 by testing the hypothesis that children with neurofibromatosis type 1 have specific planning deficits independently from intellectual level and ADHD comorbidity. Eighteen children with neurofibromatosis type 1 were pair-matched to 18 children with ADHD and 18 healthy controls. All groups were assessed on the presence of ADHD symptoms (Conners Scales) and planning deficits (Tower of London). Compared with control group, groups with neurofibromatosis type 1 and ADHD demonstrated significant impairment of planning and problem solving. The lack of correlation between Tower of London results and Conners subscale scores in neurofibromatosis type 1 group confirmed that the planning and problem-solving deficit is not directly related to inattention level. These findings suggested that the executive impairment probably represents a peculiar trait of neurofibromatosis type 1 neurocognitive phenotype.

Diffusion tensor imaging of neurofibromatosis bright objects in children with neurofibromatosis type 1

Neurofibromatosis bright objects (NBOs) are poorly understood. This article aimed to investigate: 1) differences in fractional anisotropy (FA) between NBOs based in gray matter (GM) and white matter (WM), and 2) the relationship between NBOs and the affected white matter tracts. Fourteen NF1 patients were included in this study. Apparent diffusion coefficient (ADC), FA, radial diffusivity (RD) and eigenvalues were used to compare NBOs and matching contralateral normal-appearing sites (NAS). Diffusion tensor imaging scalars were also compared with age-matched healthy controls. Fiber tractography was performed to assess NBO-induced changes in WM trajectories. ADC values were higher for GM and WM NBOs than for NAS and controls. FA values were lower in GM and WM NBOs compared with controls. In all regions, eigenvalues were higher in NBOs than in NAS and controls. Only three out of 18 NOBs appeared to disrupt WM tracts. ADC, λ2 and RD values of WM NBOs were higher in symptomatic compared to asymptomatic patients. Increased ADC, RD and eigenvalues and decreased FA values in NBOs can be explained by myelin and axonal damage. Increased ADC values and RD in WM NBOs correlated with the presence of symptoms. Tract integrity predominated in our study.

Characterizing the microstructural basis of "unidentified bright objects" in neurofibromatosis type 1: A combined in vivo multicomponent T2 relaxation and multi-shell diffusion MRI analysis

Introduction

The histopathological basis of “unidentified bright objects” (UBOs) (hyperintense regions seen on T2-weighted magnetic resonance (MR) brain scans in neurofibromatosis-1 (NF1)) remains unclear. New in vivo MRI-based techniques (multi-exponential T2 relaxation (MET2) and diffusion MR imaging (dMRI)) provide measures relating to microstructural change. We combined these methods and present previously unreported data on in vivo UBO microstructure in NF1.

Methods

3-Tesla dMRI data were acquired on 17 NF1 patients, covering 30 white matter UBOs. Diffusion tensor, kurtosis and neurite orientation and dispersion density imaging parameters were calculated within UBO sites and in contralateral normal appearing white matter (cNAWM). Analysis of MET2 parameters was performed on 24 UBO–cNAWM pairs.

Results

No significant alterations in the myelin water fraction and intra- and extracellular (IE) water fraction were found. Mean T2 time of IE water was significantly higher in UBOs. UBOs furthermore showed increased axial, radial and mean diffusivity, and decreased fractional anisotropy, mean kurtosis and neurite density index compared to cNAWM. Neurite orientation dispersion and isotropic fluid fraction were unaltered.

Conclusion

Our results suggest that demyelination and axonal degeneration are unlikely to be present in UBOs, which appear to be mainly caused by a shift towards a higher T2-value of the intra- and extracellular water pool. This may arise from altered microstructural compartmentalization, and an increase in ‘extracellular-like’, intracellular water, possibly due to intramyelinic edema. These findings confirm the added value of combining dMRI and MET2 to characterize the microstructural basis of T2 hyperintensities in vivo.

•

We examine MRI white matter T2-weighted hyperintense lesions, “UBOs” in NF1.

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Myelin water and intra- and extracellular water fractions are unchanged in UBOs.

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Diffusivity is higher, while mean kurtosis and neurite density are lower in UBOs.

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The combined measures suggest that UBOs may arise from intramyelinic edema.

•

Combining diffusion MRI and multi-exponential T2 relaxation has added value.

Evaluation of the basal ganglia in neurofibromatosis type 1

PURPOSE

Alterations of the brain microstructure and metabolism have been identified in patients with neurofibromatosis type 1 (NF1). In this study, we analyzed the basal ganglia of NF1 subjects without cognitive delay throughout a combined approach with magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) in order to better define the metabolic and microstructural characteristics of these regions and, furthermore, to verify if metabolic and microstructural abnormalities may be present in normally developed NF1 patients.

METHODS

A 3-T MRI with multivoxel MRS and DTI was performed in 14 NF1 patients and eight controls. N-acetyl-aspartate (NAA), choline (Cho), creatine (Cr) values and ratios, fractional anisotropy, and apparent diffusion coefficient (ADC) were calculated, for a total of four regions of interest (ROI) for each hemisphere.

RESULTS

NF1 patients, compared to healthy controls, showed (a) decreased NAA in all the four ROI, (b) increased Cho and decreased Cr in three of the four ROI, (c) decreased NAA/Cho ratio in three ROI, and (d) increased ADC in all the four ROI. A trend of increased ADC was present in three of the four ROI of NF1 patients with unidentified bright objects (UBOs) and younger than 18 years.

CONCLUSION

These data confirm the presence of neuroaxonal damage with myelin disturbances in NF1 patients. We showed that metabolic and microstructural anomalies can be present in the same time in NF1 patients without developmental delay or cognitive deficits. Relations between brain anomalies, UBOs, and cognitive functions need further studies.

Longitudinal assessment of cognition and T2-hyperintensities in NF1: an 18-year study

The developmental course of cognitive deficits in individuals with neurofibromatosis type 1 (NF1) is unclear. The objectives of this study were to determine the natural history of cognitive function and MRI T2-hyperintesities (T2H) from childhood to adulthood and to examine whether the presence of discrete T2H in childhood can predict cognitive performance in adulthood. We present cognitive and structural neuroimaging data from 18 patients with NF1 and five sibling controls assessed prospectively across an 18-year period. Longitudinal analyses revealed a significant increase in general cognitive function in patients with NF1 over the study period. Improvements were limited to individuals with discrete T2H in childhood. Patients without lesions in childhood exhibited a stable profile. The number of T2H decreased over time, particularly discrete lesions. Lesions located within the cerebral hemispheres and deep white matter were primarily stable, whereas those located in the basal ganglia, thalamus and brainstem tended to resolve. Our results support the hypothesis that resolution of T2H is accompanied by an improvement in general cognitive performance, possibly as a result of increased efficiency within white matter tracts.

Four-year follow-up study in a NF1 boy with a focal pontine hamartoma

Neurofibromatosis is a collective name for a group of genetic conditions in which benign tumours affect the nervous system. Type 1 is caused by a genetic mutation in the NF1 gene (OMIM 613113) and symptoms can vary dramatically between individuals, even within the same family. Some people have very mild skin changes, whereas others suffer severe medical complications. The condition usually appears in childhood and is diagnosed if two of the following are present: six or more café-au-lait patches larger than 1.5 cm in diameter, axillary or groin freckling, 2 or more Lisch nodules (small pigmented areas in the iris of the eye), 2 or more neurofibromas, optic pathway gliomas, bone dysplasia, and a first-degree family relative with Neurofibromatosis type 1. The pattern of inheritance is autosomal dominant, however, half of all NF1 cases are ‘sporadic’ and there is no family history. Neurofibromatosis type 1 is an extremely variable condition whose morbidity and mortality is largely dictated by the occurrence of the many complications that may involve any of the body systems. We describe a family affected by NF1 in whom genetic molecular analysis identified the same mutation in the son and father. Routine MRI showed pontine focal lesions in the eight-year-old son, though not in the father. We performed a four years follow-up study and at follow-up pontine hamartoma size remained unchanged in the son, and the father showed still no brain lesions, confirming thus an intra-familial phenotype variability.

Neurofibromatosis type 1: modeling CNS dysfunction

Neurofibromatosis type 1 (NF1) is the most common monogenic disorder in which individuals manifest CNS abnormalities. Affected individuals develop glial neoplasms (optic gliomas, malignant astrocytomas) and neuronal dysfunction (learning disabilities, attention deficits). Nf1 genetically engineered mouse models have revealed the molecular and cellular underpinnings of gliomagenesis, attention deficit, and learning problems with relevance to basic neurobiology. Using NF1 as a model system, these studies have revealed critical roles for the NF1 gene in non-neoplastic cells in the tumor microenvironment, the importance of brain region heterogeneity, novel mechanisms of glial growth regulation, the neurochemical bases for attention deficit and learning abnormalities, and new insights into neural stem cell function. Here we review recent studies, presented at a symposium at the 2012 Society for Neuroscience annual meeting, that highlight unexpected cell biology insights into RAS and cAMP pathway effects on neural progenitor signaling, neuronal function, and oligodendrocyte lineage differentiation.