Accelerated myelination along fiber tracts in patients with hemimegalencephaly

DWI Hyperintensity in the Fornix Fimbria on MRI in Children

BACKGROUND AND PURPOSE

The fornix-fimbria complex is mainly involved in emotions and memory. In brain MR imaging studies of young children, we have occasionally noted DWI hyperintensity in this region. The significance of this finding remains unclear. This study evaluated the DWI signal in the fornix-fimbria complex of children 0-2 years of age, including the frequency of signal hyperintensity and clinical context.

MATERIALS AND METHODS

Brain MR imaging of 714 children 0-2 years of age (mean, 11 months), performed between September 2018 and May 2021, was reviewed and evaluated for DWI signal changes in the fornix-fimbria. All children with available MR imaging studies including DWI were included. Children with poor image quality, poor visualization of the fornix-fimbria region, and missing medical data were excluded. Additional imaging findings were also evaluated. Demographic data were retrieved from the medical files. We compared the ADC values of the fimbria and fornix between children with and without signal changes. The unpaired 2-tailed Student t test and χ² test were used for statistical analysis.

RESULTS

DWI signal hyperintensity of the Fornix-fimbria complex was noted in 53 (7.4%) children (mean age, 10 months). Their mean ADC values were significantly lower than those of the children with normal DWI findings (P < .05). About half of the children had otherwise normal MR imaging findings. When detected, the most common abnormality was parenchymal volume loss (15%). The most common indication for imaging was seizures (26.5%).

CONCLUSIONS

DWI hyperintensity in the fornix-fimbria complex was detected in 7.4% of children 0-2 years of age. The etiology is not entirely clear, possibly reflecting a transient phenomenon.

Diagnostic Approach to Macrocephaly in Children

Macrocephaly affects up to 5% of the pediatric population and is defined as an abnormally large head with an occipitofrontal circumference (OFC) >2 standard deviations (SD) above the mean for a given age and sex. Taking into account that about 2-3% of the healthy population has an OFC between 2 and 3 SD, macrocephaly is considered as "clinically relevant" when OFC is above 3 SD. This implies the urgent need for a diagnostic workflow to use in the clinical setting to dissect the several causes of increased OFC, from the benign form of familial macrocephaly and the Benign enlargement of subarachnoid spaces (BESS) to many pathological conditions, including genetic disorders. Moreover, macrocephaly should be differentiated by megalencephaly (MEG), which refers exclusively to brain overgrowth, exceeding twice the SD (3SD-"clinically relevant" megalencephaly). While macrocephaly can be isolated and benign or may be the first indication of an underlying congenital, genetic, or acquired disorder, megalencephaly is most likely due to a genetic cause. Apart from the head size evaluation, a detailed family and personal history, neuroimaging, and a careful clinical evaluation are crucial to reach the correct diagnosis. In this review, we seek to underline the clinical aspects of macrocephaly and megalencephaly, emphasizing the main differential diagnosis with a major focus on common genetic disorders. We thus provide a clinico-radiological algorithm to guide pediatricians in the assessment of children with macrocephaly.

Structural MRI and tract-based spatial statistical analysis of diffusion tensor imaging in children with hemimegalencephaly

PURPOSE

To investigate the gross white matter abnormalities in the structural brain MR imaging as well as white matter microstructural alterations using tract-based spatial statistics (TBSS) analysis of diffusion tensor imaging (DTI) in both affected and contralateral cerebral hemispheres of children with hemimegalencephaly (HMEG).

METHODS

From 2003 to 2019, we retrospectively reviewed brain MR images in 20 children (11 boys, 2 days-16.5 years) with HMEG, focusing on gross white matter abnormalities. DTI was evaluated in 12 patients (8 boys, 3 months-16.5 years) with HMEG and 12 age-, sex-, and magnetic field strength-matched control subjects. TBSS analysis was performed to analyze main white matter tracts. Regions of significant differences in fractional anisotropy (FA) were determined between HMEG and control subjects and between affected and contralateral hemispheres of HMEG.

RESULTS

Gross white matter abnormalities were noted in both affected (n = 20, 100%) and contralateral hemisphere (n = 4, 20%) of HMEG. FA values were significantly decreased in both hemispheres of HMEG, compared with control subjects (P < 0.05). Contralateral hemispheres of HMEG showed regions with significantly decreased FA values compared with affected hemispheres (P < 0.05).

CONCLUSIONS

In addition to gross white matter abnormalities particularly evident in affected hemispheres, DTI analysis detected widespread microstructural alterations in both affected and contralateral hemispheres in HMEG suggesting HMEG may involve broader abnormalities in neuronal networks.

Precocious myelination in a mouse model of autism

Autism spectrum disorder (ASD) has been hypothesized to be a result of altered connectivity in the brain. Recent imaging studies suggest accelerated maturation of the white matter in young children with ASD, with underlying mechanisms unknown. Myelin is an integral part of the white matter and critical for connectivity; however, its role in ASD remains largely unclear. Here, we investigated myelin development in a model of idiopathic ASD, the BTBR mice. Magnetic resonance imaging revealed that fiber tracts in the frontal brain of the BTBR mice had increased volume at postnatal day 6, but the difference reduced over time, reminiscent of the findings in young patients. We further identified that myelination in the frontal brain of both male and female neonatal BTBR mice was increased, associated with elevated levels of myelin basic protein. However, myelin pattern was unaltered in adult BTBR mice, revealing accelerated developmental trajectory of myelination. Consistently, we found that signaling of platelet-derived growth factor receptor alpha (PDGFRα) was reduced in the frontal brain of neonatal BTBR mice. However, levels of microRNA species known to regulate PDGFRα signaling and myelination were unaltered. Together, these results suggest that precocious myelination could potentially contribute to increased volume and connectivity of the white matter observed in young children with ASD.

Disrupted cortico-ponto-cerebellar pathway in patients with hemimegalencephaly

OBJECTIVE

Cerebellar dysmaturation and injury is associated with a wide range of neuromotor, neurocognitive and behavioral disorders as well as with preterm birth. We used diffusion tensor MR imaging to investigate a disruption in structural cortico-ponto-cerebellar (CPC) connectivity in children with infantile-onset severe epilepsy.

METHODS

We performed CPC tract reconstructions in 24 hemimegalencephaly (HME) patients, 28 West syndrome (WS) of unknown etiology patients, and 25 pediatric disease control subjects without a history of epilepsy nor brain abnormality on MRI. To identify the CPC tract, we placed a seeding ROI separately in each right and left cerebral peduncle. We evaluated the distribution patterns of the CPC tracts to the cerebellum and their correlation with clinical findings.

RESULTS

In control and WS of unknown etiology groups, both sides' CPC tracts descended to bilateral hemispheres in 20 (80.0%) and 21 (75.0%); mixed (bilateral on one side and unilateral on the other side) in five (20.0%) and five (17.9%); and unilateral in zero (0.0%) and two (7.1%), respectively. However, in the HME, both sides' CPC tracts descended to bilateral hemispheres in four (16.7%); mixed in 13 (54.1%); and unilateral in seven (29.2%). These CPC patterns differed significantly between the HME and other groups (p < 0.001). Among HME patients, those with a unilateral cerebellar distribution on both sides had significantly earlier seizure onset (p = 0.049) and more frequent seizures (p = 0.052) at a trend level compared to those with bilateral and mixed distributions.

CONCLUSION

Disrupted CPC tracts were observed more frequently in HME patients than in WS of unknown etiology patients and controls, and they may be correlated with earlier seizure onset and more frequent seizures in HME patients. DTI is a useful and non-invasive method for speculating the pathology in the developing brain.

Cytotoxic edema at onset in West syndrome of unknown etiology: A longitudinal diffusion tensor imaging study

OBJECTIVE

To clarify longitudinal changes in white matter microstructures from the onset of disease in patients with West syndrome (WS) of unknown etiology.

METHODS

Diffusion tensor imaging (DTI) was prospectively performed at onset and at 12 and 24 months old in 17 children with WS of unknown etiology. DTI was analyzed using tract-based spatial statistics (TBSS) and tract-specific analysis (TSA) of 13 fiber tracts, and fractional anisotropy (FA) and mean diffusivity (MD) were compared with those of 42 age-matched controls. Correlations of FA and MD with developmental quotient (DQ) at age 24 months were analyzed. Multiple comparisons were adjusted for using the false discovery rate (q-value).

RESULTS

TBSS analysis at onset showed higher FA and lower MD in the corpus callosum and brainstem in patients. TSA showed lower MD in bilateral uncinate fasciculi (UF) (right: q < 0.001; left: q = 0.03) at onset in patients. TBSS showed a negative correlation between FA at onset and DQ in the right frontal lobe, whereas FA at 24 months old exhibited a positive correlation with DQ in the diffuse white matter. MD for bilateral UF at 24 months old on TSA correlated positively with DQ (q = 0.04, both).

SIGNIFICANCE

These findings may indicate the existence of cytotoxic edema in the immature white matter and dorsal brainstem at onset, and subsequent alterations in the diffuse white matter in WS of unknown etiology. Microstructural development in the UF might play important roles in cognitive development in WS.

Three cases of right frontal megalencephaly: Clinical characteristics and long-term outcome

AIM

To delineate the clinical and neuroimaging characteristics of localized megalencephaly involving the right frontal lobe.

METHOD

Data from three patients aged 14-16 years at the last follow-up were retrospectively reviewed.

RESULTS

All the patients were normal on neurological examination with no signs of hemiparesis. Enlargement of the right frontal lobe with increased volume of subcortical and deep white matter, as well as thickening of the ipsilateral genu of the corpus callosum was common. The onset of epilepsy was 4-7 years of age, with seizure types of massive myoclonus in two and generalized tonic-clonic in two, which could be eventually controlled by antiepileptics. Interictal electroencephalography showed frontal alpha-like activity in one, and abundant spike-wave complexes resulting in diffuse continuous spike-wave activity during sleep in two patients even after suppression of clinical seizures. Psychomotor development appeared unaffected or slightly delayed before the onset of epilepsy, but became mildly disturbed during follow-up period of 7-11 years.

CONCLUSION

Certain patients with right frontal megalencephaly can present with a milder epileptic and intellectual phenotype among those with localized megalencephaly and holohemispheric hemimegalencephaly, whose characteristic as epileptic encephalopathy was assumed from this study.

Utility of diffusion tensor imaging parameters for diagnosis of hemimegalencephaly

BACKGROUND

Hemimegalencephaly is a rare hamartomatous entity characterised by enlargement of all or part of the cerebral hemisphere ipsilaterally with cortical dysgenesis, large lateral ventricle and white matter hypertrophy with or without advanced myelination. Although conventional magnetic resonance imaging (MRI) is useful for detecting these diagnostic features, hemimegalencephaly is not always easily distinguished from other entities, especially when hemimegalencephaly shows blurring between the grey and white matter. Diffusion tensor imaging (DTI) is a functional MRI technique commonly used to assess the integrity of white matter. The usefulness of DTI in assessing hemimegalencephaly has not been fully elucidated. In this study, we clarified the characteristics of hemimegalencephaly with regard to DTI and its parameters including fractional anisotropy and apparent diffusion coefficient.

METHODS

Three patients with hemimegalencephaly underwent MRI including DTI. We first visually compared fractional anisotropy mapping and conventional MRI. Next, we quantitatively measured the fractional anisotropy and apparent diffusion coefficient values in the subcortical white matter of the hemisphere with hemimegalencephaly and corresponding normal-appearing contralateral regions and analysed the values using the Mann-Whitney U test.

RESULTS

On fractional anisotropy mapping, we could clearly distinguish the junction of grey and white matter and observed thicker white matter in the hemisphere with hemimegalencephaly, which was unclear on conventional MRI. The white matter in the hemisphere with hemimegalencephaly showed significantly higher fractional anisotropy (P<0.0001) and lower apparent diffusion coefficient (P=0.0022) values than the normal contralateral side.

CONCLUSION

DTI parameters showed salient hemimegalencephaly features and could be useful in its assessment.

Magnetic Resonance Fiber Tracking in a Neonate with Hemimegalencephaly

A magnetic resonance diffusion fiber tracking study in neonate diagnosed with left hemisphere hemimegalencephaly is presented. Despite diffuse morphologic deformities identified in conventional imaging, all major pathways were identifiable bilaterally with minor aberrations in vicinity of morphologic lesions.