Concordant biology underlies discordant imaging findings: diffusivity behaves differently in grey and white matter post acute neurotrauma

Background Cerebral edema is a common sequelum post traumatic brain injury (TBI). Quantification of the apparent diffusion coefficient (ADC) using diffusion tensor imaging (DTI) may help to characterize the pathophysiology of brain swelling.

Methods Twenty-two patients with moderate-to-severe TBI underwent magnetic resonance (MR) imaging, including DTI, within five days of injury. The mean ADCs in whole brain white matter, whole brain grey matter and entire brain were calculated and compared to twenty-five controls.

Findings A significant decrease in the grey matter ADC (p< 0.001), significant increase in the white matter ADC (p< 0.001) and no significant change in the whole brain ADC (p=0.771) was observed. No significant correlation was found between DTI parameters in any of the three regions of interest (ROI) and GCS, time to scan, intracranial pressure (ICP) before and during the time of the scan, cerebral perfusion pressure at time of scan, or Glasgow Outcome Score (GCS). Conclusions; The decrease in ADC seen in the grey matter is consistent with cytotoxic edema. The increase in ADC in the white matter indicates damage that has led to an overall less restricted diffusion. This study assists in the interpretation of the ADC by showing that the acute changes are different in the whole brain white and grey matter ROIs post TBI.