Diffusion Tensor Imaging and Volumetry of Autistic Children in India

Background:  Childhood autism is now widely viewed as having a developmental neurobiological origin. Hence localised structural and functional brain correlates have to be established. There is no major study discerning the structural and connectivity changes in the autistic children of Indian origin yet in the literature to the best of our knowledge.

Objectives:  To study the Diffusion tensor imaging (DTI) findings and compare the brain volumetry in autistic children (diagnosed as per DSMI IV criteria) as compared to age and sex matched typically developed controls.

Methods:  Study was conducted at NIMHANS, Bangalore, INDIA. After obtaining ethical approval, a study population of 19 subjects (mean age of 8.79 +/- 3.84 years; M: F=16:3) and 34 healthy controls (mean age of 12.38 +/- 3.76 years; M: F= 34:0) were imaged by a 3 Tesla MRI scanner using standard protocols. DTI data analysis was carried out using FMRIB Software Library tools version 4.1.6 to create FA maps.  Tract based spatial statistics (TBSS) analysis of the Fractional anisotropy (FA) maps was performed using voxel by voxel permutation.  Cortical reconstruction and volumetric segmentation (FSL) analysis was performed with the Freesurfer image analysis suite.

Results:  We found significantly reduced FA in bilateral corticospinal tracts, corpus callosum, left inferior longitudinal fasciculus, bilateral thalami, nucleus accumbens, left uncinate fasciculus and bilateral optic tracts. Significantly reduced volumes were found in the left accumbens, left pallidum, right thalamus, left hippocampus and bilateral cerebral white matter, after adjusting for age and intracranial volumes.

Conclusions:  Our prospective study in a small population of children with ASD under 20 years of age demonstrated significant abnormalities in various white matter tracts by TBSS analysis of DTI data as well as a few areas of significant volume reduction by FSL analysis as compared to the typically developed healthy controls. We found reduced FA and increased Radial diffusivity (RD) in many of the white matter tracts, with little effect on the Axial diffusivity (AD), suggestive of myelination defects rather than axonopathy. We also found some common areas with both reduced FA and reduced volumes, involving left nucleus accumbens and right thalamus. These data may open gateways for further research to be channelized towards these deep gray matter structures.