Fetus with MMC (IMAGE) Children's Hospital of Philadelphia Caption Part of the spinal cord and spinal nerves, usually encased in a sac, protrude through an opening in the back and is exposed to the amniotic fluid. The brainstem (hindbrain) descends, or herniates, into the spinal canal in the neck and blocks the flow of cerebrospinal fluid. This can cause a damaging buildup of fluid in the brain called hydrocephalus. Credit The Children's Hospital of Philadelphia Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.