As of 2015, experts are not sure what exactly causes fluid on the spine, according to Mayo Clinic. However, conditions that can lead to it include meningitis, a tumor on the spinal cord, an injury to the spinal cord and congenital conditions such as a tethered spinal cord, where the spinal cord is attached to abnormal tissue.
Another possible cause of fluid on the spine is a Chiari malformation, says Mayo Clinic. This is when part of the brain has descended into the spinal canal.
The fluid that collects on the spinal cord is cerebrospinal fluid; its job is to protect the spinal cord and the brain. A tumor on the spine can stop the normal flow of this fluid and cause it to form a fluid filled cyst. A tethered spinal cord also prevents cerebrospinal fluid from flowing properly, and meningitis causes an inflammation of membranes that protect the brain and the spinal cord.
Though fluid on the spinal cord can be dangerous, some people do not have symptoms and do not need treatment, according to Mayo Clinic. In other cases, fluid on the spine can lead to a curvature of the spine called scoliosis, chronic pain and problems with walking.