Usefulness of diffusion tensor imaging and fiber tractography in neurological and neurosurgical pediatric diseases

Delineating abnormal individual structural covariance brain network organization in pediatric epilepsy with unilateral resection of visual cortex

Although several previous studies have used resting-state functional magnetic resonance imaging and diffusion tensor imaging to report topological changes in the brain in epilepsy, it remains unclear whether the individual structural covariance network (SCN) changes in epilepsy, especially in pediatric epilepsy with visual cortex resection but with normal functions. Herein, individual SCNs were mapped and analyzed for seven pediatric patients with epilepsy after surgery and 15 age-matched healthy controls. A whole-brain individual SCN was constructed based on an automated anatomical labeling template, and global and nodal network metrics were calculated for statistical analyses. Small-world properties were exhibited by pediatric patients after brain surgery and by healthy controls. After brain surgery, pediatric patients with epilepsy exhibited a higher shortest path length, lower global efficiency, and higher nodal efficiency in the cuneus than those in healthy controls. These results revealed that pediatric epilepsy after brain surgery, even with normal functions, showed altered topological organization of the individual SCNs, which revealed residual network topological abnormalities and may provide initial evidence for the underlying functional impairments in the brain of pediatric patients with epilepsy after surgery that can occur in the future.

Advanced Diffusion of the Pediatric Brain and Spine

This article discusses new diffusion-weighted imaging (DWI) sequences, diffusion tensor imaging (DTI), and fiber tractography (FT), as well as more advanced diffusion imaging in pediatric brain and spine. Underlying disorder and pathophysiology causing diffusion abnormalities are discussed. Multishot echo planar imaging (EPI) DWI and non-EPI DWI provide higher spatial resolution with less susceptibility artifact and distortion, which are replacing conventional single-shot EPI DWI. DTI and FT have established clinical significance in pediatric brain and spine. This article discusses advanced diffusion imaging, including diffusion kurtosis imaging, neurite orientation dispersion and density imaging, diffusion spectrum imaging, intravoxel incoherent motion, and oscillating-gradient spin-echo.

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.

Corticospinal tract mapping in children with ruptured arteriovenous malformations using functionally guided diffusion-tensor imaging

Arteriovenous malformations (AVMs) can lead to distortion or reorganization of functional brain anatomy, making localization of eloquent white matter tracts challenging. To improve the accuracy of corticospinal tract (CST) mapping, recent studies have examined the use of functional imaging techniques to help localize cortical motor activations and use these as seed points to reconstruct CSTs using diffusion-tensor imaging (DTI). The authors examined the role of pretreatment functionally guided DTI CST mapping in 3 children with ruptured AVMs. In 2 patients, magnetoencephalography motor activations were adjacent to the nidus and/or hemorrhagic cavity. However, in 1 child, functional MRI motor activations were detected in both hemispheres, suggestive of partial transfer of cortical motor function. In all children, quantitative analysis showed that fractional anisotropy values and fiber density indices were reduced in the CSTs of the hemisphere harboring the AVM compared with the unaffected side. In 2 children, CST caliber was slightly diminished, corresponding to no motor deficit in 1 patient and a temporary motor deficit in the other. In contrast, 1 child demonstrated marked reduction and displacement of the CSTs, correlating with severe motor deficit. Preoperative motor tractography data were loaded onto the intraoperative neuronavigation platform to guide complete resection of the AVM in 2 cases without permanent neurological deficits. These preliminary results confirm the feasibility of CST mapping in children with ruptured AVMs using functionally guided DTI tractography. Prospective studies are needed to assess the full value of this technique in the risk stratification, prognosis, and multimodality management of pediatric AVMs.

Normal and abnormal development of the cerebellum and brainstem as depicted by diffusion tensor imaging

Diffusion tensor imaging (DTI) is an advanced MRI technique that measures the microscopic molecular motion of water to gain information about the brain structure. This modality and its application to fiber tractography have been increasingly used in the last years to study the neuroanatomical background of brain malformations. This article aims to give an overview of the application of DTI and fiber tractography on pediatric posterior fossa including malformations, acquired disorders affecting the white matter, and posterior fossa involvement in phacomatoses. For every disorder, we show the additional information that DTI and fiber tractography are providing compared to conventional MR sequences and discuss their significance. Additionally, we show at the beginning normal DTI and fiber tractography findings of the pediatric posterior fossa. Finally, we briefly discuss potential future uses for DTI and fiber tractography to further understand the pathogenesis of posterior fossa malformations and the neuronal plasticity and connectivity of acquired lesions affecting the posterior fossa.

Advanced magnetic resonance imaging techniques in the evaluation of pediatric white matter diseases

This article aimed to describe the technical principles and clinical application of advanced magnetic resonance imaging techniques for the assessment of white matter diseases. The following techniques are going to be discussed: magnetization transfer, proton magnetic resonance spectroscopy, diffusion-weighted imaging, diffusion tensor imaging, as well as perfusion and postprocessing techniques such as tract-based spatial statistics. These techniques allow a better understanding of the physiopathology of the white matter diseases as well as have a significant impact on the definition of the differential diagnosis and treatment options.

Fiber tractography assessment in double cortex syndrome

INTRODUCTION

Subcortical band heterotopia (SBH) or double cortex syndrome is a malformation of cortical development that may be related to intractable epilepsy and severe mental retardation or to mild epilepsy and slight mental delay or normal cognitive functions. Several studies have been performed using neuroradiological or neurophysiological techniques, like SPECT, PET, MRS, fMRI, and MEG, in attempt to better characterize this neuronal migration disorder. Recently, also diffusion tensor imaging (DTI) and fiber tracking (FT) have been used to investigate on white matter anomalies in SBH, adding more information about such gray matter anomaly.

METHODS

We report on three cases of SBH, evaluated with MRI, DTI, and FT.

CONCLUSIONS

The data gathered from DTI and TF allow us to hypothesize a new functional role for heterotopic gray matter.

[Neuroimaging of multiple sclerosis in children]

There is an increasing appreciation that multiple sclerosis (MS) can affect children. Up to 10% of MS patients experience their first symptoms before the age of 16. The natural history and magnetic resonance imaging of MS in child-hood differ from those observed in adult patients. The differential diagnosis of MS in children should also encompass some paediatric diseases. Recently, the diagnostic criteria for MS in children were published. Due to the high frequency of relapses and the risk of disability at a young age, early diagnosis and treatment of MS in children is very important. This work presents recent data regarding epidemiology, pathogenesis and diagnosis of MS in children, including the role of neuroimaging in the diagnosis of childhood multiple sclerosis.