Cognitive recovery correlates with white-matter restitution after head injury

Longitudinal measurements of local cerebral perfusion (LCBF) and local partition coefficients (L lambda) using xenon-enhanced computed tomography were examined in six patients who had suffered from head injury at a mean age of 30 +/- 9.3 years. They were selected from a larger group with head injury because all were observed longitudinally to make excellent cognitive recovery some years after acute cerebral trauma. Results were compared with similar longitudinal measurements made in six age-matched neurologically normal volunteers. In the index group, cognitive test scores were reduced at the time of the first LCBP measurement but significantly improved to normal at the time of the second. The mean interval between measurements was 2.7 +/- 0.7 years. At the time of the first measurement, all six patients exhibited abnormal volumes of white matter with reduced Hounsfield numbers and LCBF and L lambda values. Abnormalities in volume of white matter and LCBF and L lambda values improved to normal at the time of the second measurement. Perfusion values for frontal cortex, putamen, and thalamus were still slightly reduced but also improved toward normal between measurements. Cognitive recovery correlated best with restoration of white matter integrity, suggesting that following head injury, cognitive impairments may be associated with temporary disconnections of corticothalamic projection systems.