Original ArticleDiffusion Tensor Imaging of Aicardi Syndrome
Introduction
Aicardi syndrome, a congenital neurodevelopmental disorder associated with severe cognitive and motor impairment, is defined by the diagnostic triad of corpus callosum dysgenesis, chorioretinal lacunae, and infantile spasms [1], [2]. Other common neurologic findings include polymicrogyria, periventricular and subcortical heterotopia, and choroid plexus papillomas [3]. Although the anatomic features of Aicardi have been well described under conventional neuroimaging [4], little is known about the underlying white matter structural organization of individuals with Aicardi syndrome.
Diffusion tensor imaging (DTI) is a modality of magnetic resonance imaging that characterizes the microstructural organization of major white matter tracts by measuring the degree of anisotropic diffusion of water within the brain [5]. Because water diffuses preferentially along the axis of axonal fiber bundles, the direction of greatest diffusion indicates the course of major white matter fibers, whereas the degree of diffusion anisotropy is an indication of white matter microstructural integrity. In recent years, DTI has increasingly been used to investigate neurodevelopmental disorders, including agenesis of the corpus callosum [6], [7], horizontal gaze palsy with progressive scoliosis [8], [9], pontine tegmental cap dysplasia [10], [11], and holoprosencephaly [12], [13]. Presented here are DTI findings for two subjects with Aicardi syndrome in whom substantial alterations to white matter organization were revealed.
Section snippets
Patient Histories
Aicardi subject 1 was a 10-year-old girl, born at 38 weeks to a 31-year-old gravida 2 mother. Parents were nonconsanguineous. Because 30-week prenatal ultrasound investigation suggested hydrocephalus, postnatal MRI was performed, which revealed agenesis of the corpus callosum. The child's weight at birth was 3374 g. The child remained in the hospital for 7 days after birth because of jaundice.
Bilateral chorioretinal lacunae were documented at 3 months. The left macula lacunae were more severe
Results
For the anatomic abnormalities evident on conventional imaging (discussed in the Patient Histories section), representative T1-weighted structural images are shown in Figure 1 (panels A and D). Because of the absence of speech or comprehension in both patients, the initial assay was of the integrity of the arcuate fasciculus (superior longitudinal fasciculus) by DTI. On DTI color fractional anisotropy images, longitudinal fibers were bilaterally absent or severely diminished in the expected
Discussion
The present data support the hypothesis that cortical white matter organization is profoundly disrupted in individuals with Aicardi syndrome. In both subjects, greatly diminished corticocortical connectivity was noted, with only the right inferior fronto-occipital fasciculus, and bilateral Probst bundles present in one subject, and bilateral cingulum bundles and left uncinate fasciculus present in another. Subcortical white matter fibers were grossly normal, suggesting that white matter
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Both authors contributed equally to this work.