Flows of cerebrospinal fluid during brain injury

During stroke, cardiac arrest, and traumatic brain injury, a primary cause of irreversible tissue damage is the severe swelling that ensues as fluid rushes into the brain. That fluid was long believed to come from the bloodstream. Though much does eventually come from blood, my collaborators and I recently showed that in the first half hour, nearly all comes instead from the cerebrospinal fluid (CSF) that surrounds the brain and fills the perivascular spaces around its blood vessels. In vivo particle tracking revealed that during injury, CSF reverses its flow direction and rushes into the tissue, concomitant with a spreading wave of sudden constrictions of nearby arteries. A simple fluid dynamical model reproduced much of the observed dynamics. MRI imaging and radiolabeled tracers confirmed that CSF is the source of swelling. Knowing that swelling is caused by pathological CSF circulation leads to new ideas for treatment during brain injury, such as promoting clearance of CSF from the brain, not only in the first half-hour but throughout the recovery period.