Diffusion-tensor MR imaging and fiber tractography: a new method of describing aberrant fiber connections in developmental CNS anomalies.
Congenital anomalies of the central nervous system (CNS) often demonstrate aberrant white matter connections, which may be better characterized with diffusion-tensor imaging (DTI) and fiber tractography (FT) than with conventional magnetic resonance (MR) imaging. DTI-FT demonstrates abnormal hemispheric fiber connections in callosal agenesis or acquired disease of the corpus callosum. Decreased anisotropy of white matter adjacent to the malformed cortex and an aberrant course of major fiber pathways due to dysplastic white matter are common findings in cortical dysplasia. Increased anisotropy of dysplastic gray matter in heterotopia supports the hypothesis that developing neurons migrate from the ependyma to the cortex with a radial growth pattern. In periventricular leukomalacia, DTI-FT demonstrates an intact corticospinal tract and decreased thalamocortical sensory connections, which are responsible for the spasticity of cerebral palsy owing to impairment of inhibitory function. Joubert syndrome comprises malformation of the cerebellar vermis and an aberrant connection between the cerebellum and the cerebral cortex via an elongated and abnormally shaped superior cerebellar peduncle, which are well visualized with DTI-FT. In developmental CNS disease, DTI-FT demonstrates additional findings beyond those seen with conventional MR imaging. Future studies will focus on determining the significance of the aberrant fiber connections and their relationships to the clinical manifestations of CNS anomalies.