Quantitative diffusion tensor imaging in cerebral palsy due to periventricular white matter injury

Periventricular white matter injury (PWI) is a major form of brain injury observed in congenital hemiparesis. The aim of this study is to determine the usefulness of diffusion tensor imaging (DTI) and fibre tracking in delineating the primary and secondary degenerative changes in cerebral white matter and deep grey matter in patients with spastic cerebral palsy due to PWI and to look for any possible reorganization of the axonal architecture. Five hemiparetic cerebral palsy patients (median age 14 years) with known PWI were prospectively studied with DTI of the brain at 1.5T and quantitatively compared with five age and sex matched controls. Fibre tracts for various corticofugal, thalamocortical and association tracts were generated and analysed for the DTI fibre count and for diffusion parameters. A region of interest based analysis was performed for the directionally averaged mean diffusivity (D(av)) and fractional anisotropy (FA) values in various white matter locations in the brain and the brainstem and in the deep grey matter nuclei. Group statistics were performed for these parameters using Mann-Whitney U-test comparing the affected sides in patients with either side in controls and the unaffected side in hemiparetics. There was significant reduction in DTI fibre count on the lesional side involving corticospinal tract (CST), corticobulbar tract (CBT) and superior thalamic radiation in the patient group compared with controls. Also there was an increase in DTI fibre count in the unaffected side of the hemiparetic patients in CST and CBT, which reached statistical significance only in CBT. The corpus callosum, cingulum, superior longitudinal fasciculus and middle cerebellar peduncle failed to show any significant change. ROI measurements on the primary site of white matter lesion and the thalamus revealed a significant increase in D(av) and decrease in FA, suggesting primary degeneration. The CST in the brainstem, the body of corpus callosum and the head of caudate and lentiform nuclei showed features of secondary degeneration on the affected side. The CST on the unaffected side of hemiparetics was found to have a significant decrease in D(av) and an increase in FA. Thus the degeneration of various motor and sensory pathways, as well as deep grey matter structures, appears to be important in determining the pathophysiological mechanisms in patients with congenital PWI. Also evidence suggesting the reorganization of sensorimotor tracts in the unaffected side of spastic hemiparetic patients was noted.