Cerebrospinal fluid (csf) is a watery fluid that continually circulates through the brain’s ventricles (hollow cavities) and around the surface of the brain and spinal cord. A csf leak occurs when the … A cerebrospinal fluid leak (csf leak or csfl) is a medical condition where the cerebrospinal fluid (csf) that surrounds the brain and spinal cord leaks out of one or more holes or tears in the dura mater.