In the United States, 1 in every 770 babies develops hydrocephalus. Hydrocephalus that is present at birth is referred to as congenital hydrocephalus. Hydrocephalus that develops later in life in some children, and even in adults, but is caused by a condition that existed at birth, is still considered a form of congenital hydrocephalus. Congenital hydrocephalus is caused by a complex interaction of genetic and environmental factors during fetal development. The genetic causes of hydrocephalus are still being studied. There are likely many genes that can cause hydrocephalus or be a risk factor for increasing the likelihood of developing hydrocephalus.
Causes of Congenital Hydrocephalus
Aqueductal stenosis – The most common cause of congenital hydrocephalus is an obstruction called aqueductal stenosis. This occurs when the long, narrow passageway between the third and fourth ventricles (the aqueduct of Sylvius) is narrowed or blocked, perhaps because of infection, hemorrhage, or a tumor. Fluid accumulates “upstream” from the obstruction, producing hydrocephalus.
Neural tube defect – Another common cause of hydrocephalus is a neural tube defect (NTD). An open NTD, where the spinal cord is exposed at birth and is often leaking CSF, is called myelomeningocele and is often referred to as spina bifida. This kind of NTD usually leads to the Chiari II malformation, which causes part of the cerebellum and the fourth ventricle to push downward through the opening at the base of the skull into the spinal cord area, blocking CSF flow out of the fourth ventricle and causing hydrocephalus. For more information please visit the National Institute of Neurological Disorders and Stroke (NINDS) and Spina Bifida Association.
Arachnoid cysts – Congenital hydrocephalus can also be caused by arachnoid cysts, which may occur anywhere in the brain. In children, they’re often located at the back of the brain (posterior fossa) and in the area of the third ventricle. These cysts are filled with CSF and lined with the arachnoid membrane, one of the three meningeal coverings. Some arachnoid cysts are self-contained, while others are connected with the ventricles or the subarachnoid space. The fluid trapped by the cysts may block the CSF pathways, causing hydrocephalus.
Dandy-Walker syndrome – In Dandy-Walker syndrome, another cause of congenital hydrocephalus, the fourth ventricle becomes enlarged because its outlets are partly or completely closed and part of the cerebellum fails to develop. Dandy-Walker syndrome may also be associated with abnormal development in other parts of the brain and sometimes leads to aqueductal stenosis. In some instances, two shunts are placed in the child’s ventricles — one in the lateral ventricle and another in the fourth ventricle to manage the hydrocephalus. Please visit the National Institute of Neurological Disorders and Stroke (NINDS) for more information on Dandy-Walker syndrome.
Chiari malformation – There are four types of Chiari malformation. Hydrocephalus is most commonly associated with Chiari I malformation or Chiari II malformation. Both types occur at the bottom of the brain stem where the brain and spinal cord join. The lowest portion of the brain is displaced and is lower than normal, pushing down into the spinal column. Please visit the National Institute of Neurological Disorders and Stroke (NINDS) for more information on Chiari malformation.
X-linked hydrocephalus – is a rare genetic disorder that occurs in about 1 of 30,000 births. X-linked hydrocephalus is characterized by stenosis, or narrowing, of the aqueduct of Sylvius and severe ventriculomegaly. It is part of a group of conditions linked by mutations in the L1CAM gene. Collectively the conditions are called L1 syndrome, whose symptoms can vary greatly in severity, and include, MASA (mental retardation, adducted thumbs, shuffling gait and aphasia) syndrome, certain forms of X-linked spastic paraplegia (SPG1), and X-linked agenesis of the corpus callosum (ACC). For more detailed information, visit Finding Our Way with L1CAM.
For more detailed information on genetics and hydrocephalus, visit Genetic Mutations and their Role in Congenital Hydrocephalus and Genetic Causes of Hydrocephalus.
Information you can trust! This article has been reviewed by members of our Medical Advisory Board and other professionals in the field.