Major frontal lobe tracts and corpus callosum (CC) were investigated in 32 children with autism spectrum disorder (ASD, mean age: 5 years), 12 nonautistic developmentally impaired children (DI, mean age: 4.6 years), and 16 typically developing children (TD, mean age: 5.5 years) using diffusion tensor imaging tractography and tract-based spatial statistics. Various diffusion and geometric properties were calculated for uncinate fasciculus (UF), inferior fronto-occipital fasciculus (IFO), arcuate fasciculus (AF), cingulum (Cg), CC, and corticospinal tract. Fractional anisotropy was lower in the right UF, right Cg and CC in ASD and DI children; in right AF in ASD children; and in bilateral IFO in DI children, compared with TD children. Apparent diffusion coefficient was increased in right AF in both ASD and DI children. The ASD group showed shorter length of left UF and increased length, volume, and density of right UF; increased length and density of CC; and higher density of left Cg, compared with the TD group. Compared with DI group, ASD group had increased length, volume, and density of right UF; higher volume of left UF; and increased length of right AF and CC. Volume of bilateral UF and right AF and fiber density of left UF were positively associated with autistic features.

Children with autistic spectrum disorder are known to have histopathological abnormalities in the cerebellum. Diffusion tensor imaging has been utilized to study abnormalities in connectivity and microintegrity in brains of such children. A region of interest approach was adopted to study cerebellar outflow and inflow pathways in 27 children (24 males; mean age, 5.0 years) with autism, and comparison was made with 16 normally developing controls. An increase in the mean diffusivity of bilateral superior cerebellar peduncles in those with autistic spectrum disorder was noted, as was a reversal of the asymmetry pattern in fractional anisotropy of the middle cerebellar peduncle and the inferior cerebellar peduncle in the autistic spectrum disorder group, compared with controls. This study reiterates the underconnectivity between the cerebellum and neocortex, using diffusion tensor imaging.

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