Diffusion tensor MRI was used to evaluate the effects of cerebral white matter (WM) injury on subsequent microstructural brain development in 20 premature infants studied at Children’s Hospital, Harvard Medical School, Boston, MA. Cerebral WM injury identified by conventional MRI within the first 3 weeks of life in 10 infants was examined by diffusion tensor MRI at term. Relative anisotropy (RA), a measure of preferred directionality of perfusion (and dependent on axonal and oligodendroglial development) was 25% lower in central WM, the site of the original injury, and 20% lower in the internal capsule that carries fibers from the injured WM. Diffusion vector maps showed alterations in the microstructure of the damaged WM and descending fiber tracts. 
COMMENT. Perinatal cerebral white matter injury may result in both an immediate local tissue destruction and a subsequent impairment of brain development affecting fiber tracts and distal structures. These late effects of injury could reflect a Wallerian degeneration in the posterior limb of the internal capsule and a maldevelopment of axonal-oligodendroglial structures. They may explain the MRI finding of asymmetrical hypomyelination of the internal capsule and hemiplegia as sequelae of perinatal ventricular hemorrhage.
Dissociated cortical motor reorganization following brain injury. Differences in interhemispheric organization of sensory and motor pathways in cerebral palsy (CP) have been studied, using transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI), in 7 subjects with hemiplegic CP (ages 15-57 years) at the University of Western Australia and the Princess Margaret Hospital for Children, Nedlands and Subiaco, Australia . Normal contralateral motor and sensory projections were demonstrated between the unaffected hand and the cerebral hemisphere. Passive movement of the affected hand caused fMRI contralateral activation, whereas TMS indicated either an ipsilateral projection or asymmetrical bilateral projection. Some of the motor dysfunction in the affected hand in CP may be due to a dissociation between sensory and motor representations in cortical reorganization.