Classifications and Causes
Hydrocephalus is a condition, not a disease. It can develop for a variety of reasons, sometimes as part of another condition.
Congenital hydrocephalus means the condition is present at birth, caused by a complex interaction of genetic and environmental factors during fetal development. Congenital hydrocephalus is now often diagnosed before birth through routine ultrasound.
Compensated hydrocephalus is hydrocephalus that is diagnosed in adulthood, but may have existed since birth. It can still be considered congenital.
Acquired hydrocephalus develops after birth as a result of neurological conditions such as head trauma, brain tumor, cyst, intraventricular hemorrhage or infection of the central nervous system.
Normal pressure hydrocephalus occurs in older adults when the ventricles of the brain are enlarged, but there is little or no increase in the pressure within the ventricles. Sometimes the cause of NPH is known – but most often it is idiopathic, which means the cause is not known.
Another set of terms you may hear from a doctor to describe hydrocephalus are “communicating” and “non-communicating.” If the cerebrospinal fluid (CSF) flows freely throughout the brain’s ventricular system and the subarachnoid space, it is referred to as communicating hydrocephalus. If there is a physical blockage such as a tumor somewhere in that system, it is called non-communicating hydrocephalus.
Common 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 a 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.
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.
Chiari malformation – There are two types of Chiari malformation. Both types occur in 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.
Common Causes of Acquired Hydrocephalus
Intraventricular hemorrhage – An intraventricular hemorrhage, which most frequently affects premature newborns, may cause an acquired form of hydrocephalus. When small blood vessels alongside the ventricular lining rupture, blood may block or scar the ventricles or plug the arachnoid villi, which allow CSF to be absorbed. When the CSF can’t be absorbed, hydrocephalus results.
Meningitis – Meningitis is an inflammation of the membranes of the brain and spinal cord. Caused by a bacterial or (less frequently) viral infection, meningitis can scar the delicate membranes called meninges that line the CSF pathway. An acquired form of hydrocephalus may develop if this scarring obstructs the flow of CSF as it passes through the narrow ventricles or over the surfaces of the brain in the subarachnoid space.
Head injury – A head injury can damage the brain’s tissues, nerves, or blood vessels. Blood from ruptured vessels may enter the CSF pathway, causing inflammation. Sites of CSF absorption might then be blocked by scarred membranes – meninges – or by blood cells. The CSF flow is restricted, and hydrocephalus develops.
Brain tumors – In children, brain tumors most commonly occur in the back of the brain which is referred to as the posterior fossa. As a tumor grows, it may fill or compress the fourth ventricle, blocking the flow of CSF and causing hydrocephalus. A tumor somewhere else in the brain might also block or compress the ventricular system.
Symptoms of Hydrocephalus
The symptoms of untreated hydrocephalus vary. During pregnancy, routine ultrasound can detect enlarged ventricles or spaces within a baby’s brain. In an infant, the most obvious sign of hydrocephalus is an abnormal enlargement of the baby’s head. In children symptoms tend to be related to high pressure and may include nausea, vomiting, headache and vision problems.
In young and middle aged adults symptoms most often include dizziness and vision problems. In older adults with normal pressure hydrocephalus (NPH) the symptoms are more likely to be loss of function in three main areas: walking, thinking and bladder control.
Infants and Children
Young and Middle Aged Adults
Older Adults (NPH)
The most common initial diagnostic test to determine hydrocephalus at any age is an image of the brain using CT or MRI to identify if the ventricles or spaces within the brain are enlarged. More tests are often performed in adults in order to diagnosis the condition. The decision to order a particular test may depend on the specific clinical situation, as well as the preference and experience of the medical team. Not all of the tests described here are required in order to make a diagnosis.
The following links provide information about the signs, symptoms and diagnostic tests for hydrocephalus in various age groups.
There is currently no known way to prevent or cure hydrocephalus and the only treatment option today requires brain surgery. With early detection and appropriate intervention of hydrocephalus, the future for many is promising. Recent research is advancing knowledge and moving us closer to a cure. Advances in technology as well as diagnostic and treatment protocols are helping more and more people with hydrocephalus to lead full and active lives.
There are three forms of surgical treatment currently used to manage hydrocephalus.
The most common treatment for hydrocephalus—and the most common procedure performed by pediatric neurosurgeons in the United States—is the surgical implantation of a device called a shunt.
A shunt is a flexible tube placed into the ventricular system of the brain which diverts the flow of CSF into another region of the body, most often the abdominal cavity, where it can be absorbed. A valve within the shunt maintains CSF at normal pressure within the ventricles.
A second treatment option for hydrocephalus is a surgical procedure called endoscopic third ventriculostomy (ETV). This same ETV procedure with the addition of choroid plexus cauterization is available for infants. In the ETV procedure, an endoscope is used to puncture a membrane in the floor of the third ventricle creating a pathway for CSF flow within the cavities in the brain. This approach is an important alternative to shunting for obstructive hydrocephalus and may be useful in other cases as well.
The third treatment option involves the addition of choroid plexus cauterization with endoscopic third ventriculostomy in infants. The neurosurgeon uses a device to burn or cauterize tissue from the choroid plexus. The choroid plexus is a network of vessels in the ventricles of the brain where cerebrospinal fluid is produced.
The success rate for ETV or ETV/CPC depends upon patient factors such as age, cause of hydrocephalus, and whether there is scarring in the fluid space below the floor of the third ventricle. For some patients, the chance for success of the ETV may be up to 90%; however, for others, ETV – with the addition of CPC for infants – may not be recommended because the chances for success are sufficiently low. Your neurosurgeon should be able to provide you with a reliable estimate of the likelihood for success in your particular situation prior to the operation. It’s critical that parents and patients understand that ETV is not always a permanent cure for hydrocephalus. Candid communication with your physician regarding the definition of success is important when considering ETV.