Contribution of edema and cerebral blood volume to traumatic brain swelling in head-injured patients

Object. The pathogenesis of traumatic brain swelling remains unclear. The g enerally held view is that brain swelling is caused primarily by vascular e ngorgement and that edema plays a relatively minor role in the swelling pro cess. The goal of this: study was to examine the roles of cerebral blood vo lume (CBV) and edema in traumatic brain swelling. Methods. Both brain-tissue water and CBV were measured in 76 head-injured p atients, and the relative contribution of edema and blood to total brain sw elling was determined. Comparable measures of brain-tissue water were obtai ned in 30 healthy volunteers and CBV in seven volunteers. Brain edema was m easured using magnetic resonance imaging, implementing a new technique fur accurate measurement of total tissue water. Measurements of CBV in a subgro up of 31 head-injured patients were based on consecutive measures of cerebr al blood flow (CBF) obtained using stable xenon and calculation of mean tra nsit time by dynamic computerized tomography scanning after a rapid bolus i njection of iodinated contrast material. The mean (+/- standard deviation) percentage of swelling due to water was 9.37 +/- 8.7%, whereas that due to blood was -0.8 +/- 1.32%. Conclusions. The results of this study showed that brain edema is the major fluid component contributing to traumatic brain swelling. Moreover, CBV is reduced in proportion to CBF reduction following severe brain injury.