Diffusion tensor imaging of Aicardi syndrome

Abstract

Aicardi syndrome is a congenital neurodevelopmental disorder associated with significant cognitive and motor impairment. Diffusion tensor imaging was performed on two subjects with Aicardi syndrome, as well as on two matched subjects with callosal agenesis and cortical malformations but not a clinical diagnosis of Aicardi syndrome. Whole-brain three-dimensional fiber tractography was performed, and major white matter tracts were isolated using standard tracking protocols. One Aicardi subject demonstrated an almost complete lack of normal corticocortical connectivity, with only the left inferior fronto-occipital fasciculus recovered by diffusion tensor tractography. A second Aicardi subject exhibited evidence of bilateral cingulum bundles and left uncinate fasciculus, but other corticocortical tracts were not recovered. Major subcortical white matter tracts, including corticospinal, pontocerebellar, and anterior thalamic radiation tracts, were recovered in both Aicardi subjects. In contrast, diffusion tensor tractography analysis on the two matched control subjects with callosal agenesis and cortical malformations recovered all major intrahemispheric cortical and subcortical white matter tracts. These findings reveal a widespread disruption in the corticocortical white matter organization of individuals with Aicardi syndrome. Furthermore, such disruption in white matter organization appears to be a feature specific to Aicardi syndrome, and not shared by other neurodevelopmental disorders with similar anatomic manifestations.

Fig 1

T1-weighted and DTI images of Aicardi subjects and acallosal control subjects. T1-weighted coronal images are shown for subject 1 (A) and matched control subject (D). Coronal DTI colormaps are also shown for subject 1 (B), subject 2 (C), and their matched controls (E, F respectively). Yellow arrows indicate expected location of superior longitudinal fasciculus, normally visible as green longitudinal fibers. The superior longitudinal fasciculus is greatly diminished or absent in Aicardi subjects, while grossly intact in acallosal controls. Fiber orientation on DTI colormaps is encoded as: anterior-posterior, green; superior-inferior, blue; left-right, red.

Fig 2

Cortico-cortical connectivity of Aicardi subjects and acallosal controls. DTI tractography shows bilateral Probst bundles and right inferior fronto-occipital fasciculus (IFO) for subject 1 (A, right; B, left) and bilateral cingulum bundles and left uncinate fasciculus for subject 2 (C, right; D, left). Matched acallosal controls demonstrate all major cortico-cortical tracts (E-H), with the exception of the right arcuate fasciculus in the control matched for subject 2 (H). Tracts are colored as follows: cingulum bundle or probst bundle (orange), inferior fronto-occipital fasciculus (red), uncinate fasciculus (white), inferior longitudinal fasciculus (green), arcuate fasciculus (yellow).

Fig 3

Subcortical connectivity of Aicardi subjects and acallosal controls. DTI tractography reveals grossly intact anterior thalamic radiations (yellow), corticospinal tracts (blue), and middle cerebellar peduncles (red) in both Aicardi subjects (A-D) and acallosal controls (E-H). Images are lettered as in Fig 2.