If you’re a pregnant mother worrying over a not-so-good ultrasound report or the parent of a child whose head is growing mysteriously larger, you may have been informed or heard about hydrocephalus. Alternatively, you may be concerned about an elderly friend or relative whose mental faculties have deteriorated and who is having trouble walking, all symptoms of this rare condition. Hydrocephalus is the abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain and can affect newborns, children, and adults.
The function of CSF is to bathe the brain and spinal cord, offering protection and nourishment. It also transports waste away from the surrounding tissues. The production and absorption of CSF is a continuous process. While the brain generates new CSF in its four ventricles, the old fluid is absorbed by the bloodstream. When there is an imbalance between the rate of production and the rate of absorption of CSF, the fluid accumulates, leading to hydrocephalus.
The term hydrocephalus is derived from the Greek language – “hydro” meaning water and “cephalus” meaning head. While “water in the head” used to be considered an apt description for hydrocephalus, it is a misnomer since it’s not water but CSF that surrounds the brain.
Hydrocephalus in unborn babies is quite different from hydrocephalus that develops during childhood. And hydrocephalus in elderly patients develops for yet another set of reasons. While the exact causes are still not known, some conditions can act as triggers. Here’s a closer look at the causes of hydrocephalus, based on these broad age-wise categories.
Causes Of Congenital Hydrocephalus In Babies
The classic enlarged head associated with hydrocephalus is generally seen in babies and young children. The head swells up to accommodate the excess fluid.
1. Spina Bifida
Spina bifida is a neural tube defect that can lead to hydrocephalus. The neural tube begins to grow in the earliest stages of pregnancy and closes when the fetus is about four weeks old. It later develops into the brain, spinal chord, and nerves. But, sometimes, a part of the neural tube fails to develop or doesn’t close. This can force the fourth ventricle and part of the cerebellum to push downward through the lower part of the skull into the spinal cord area, restricting the flow of CSF from the fourth ventricle, and thereby leading to hydrocephalus.5
2. Premature Birth
Complications during a premature delivery can also cause hydrocephalus. Some premature babies develop bleeding in the brain and this blocks the normal flow of CSF. The accumulated fluid leads to hydrocephalus.
id="3-dandy-walker-syndrome">3. Dandy-Walker Syndrome
This is a rare malformation of the cerebellum, the part of the brain that controls movement. In this condition, the fourth ventricle, which allows CSF to flow between the upper and lower parts of the brain and spinal cord, becomes enlarged, causing fluid to accumulate in the brain. The symptoms can be spotted soon after birth. A baby with Dandy-Walker syndrome has slow motor development. Their head also becomes progressively larger.6 7
4. Aqueductal Stenosis
This is a genetic abnormality and a common cause of congenital hydrocephalus. A block in the long and narrow aqueduct or channel between the third and fourth ventricles of the brain prevents the flow of CSF. The accumulation of fluid leads to hydrocephalus. The obstruction may be caused by a tumor, infection, or bleeding.8
5. Arachnoid Cysts
These are sacs filled with CSF and can occur anywhere in the brain. This congenital defect is usually found at the back of the brain in children. The sacs can obstruct the narrow pathways through which CSF flows, resulting in hydrocephalus.9 They can also develop as a result of trauma or injury.
6. Chiari Malformation
Chiari malformation can also occur later in life due to injury, trauma, or infection and involving excess drainage of the spinal fluid (acquired or secondary Chiari malformation).
These occur at the base of the brain stem where the brain and spinal cord meet. Chiari 1 is the most commonly occurring malformation among four such types. In this condition, the underside of the back of the brain grows into the spinal canal. As it presses against the brain stem and spinal cord, it obstructs the draining of CSF, leading to hydrocephalus. Babies with this condition may have breathing problems and difficulty in swallowing and may be irritable when fed. They may also gag or vomit often and have a stiff neck and weak arms.10 11
Causes Of Acquired Hydrocephalus In Children And Adults
Once the skull bones are mature and fused, as in older kids and adults, hydrocephalus manifests not as a swollen head but as painful headaches because of the extra pressure on the head.12
This category of hydrocephalus develops after a baby is born and also occurs among older children and adults. It is “acquired” as a result of various neurological problems such as:
- Bleeding in the ventricles, called intraventricular hemorrhage
- Infections, such as meningitis or mumps
- Trauma to the head
- Brain tumor
As children grow older, acquired hydrocephalus manifests in symptoms like downward-gazing eyes, awkward movements, problems with vision and balance, drowsiness, headache, memory loss, incontinence, and nausea.
1. Intraventricular Hemorrhage
This often occurs with prematurely born babies, when tiny blood vessels near the surface of the ventricles break open. The blood that leaks out can block the ventricles or scar them or form plugs inside the tiny tubes called arachnoid villi that normally absorb CSF. When CSF fails to get absorbed, it accumulates and leads to hydrocephalus.
Meningitis, caused usually by a bacterial (or sometimes, a viral) infection, leads to inflammation of the membranes of both brain and spinal cord. This results in the scarring of the fine membranes lining the vessels that transport CSF. Hydrocephalus can develop if the scarring blocks the fluid as it flows through the ventricles or the brain surfaces.
If brain tissue, nerves, or blood vessels are damaged as a result of head injury, inflammation may set in when vessels break and blood enters the CSF channels. The sites where CSF is absorbed may get blocked by scarred membranes or blood cells and the interrupted flow of CSF causes hydrocephalus.
4. Brain Tumors
Brain tumors in children generally develop in a region known as posterior fossa, at the back of the brain. As the tumor grows, it fills or presses the fourth ventricle, obstructing CSF from flowing, which leads to hydrocephalus. Tumors growing elsewhere in the brain may also block or push against the ventricles, with the same result.13 14 15
Causes Of Normal Pressure Hydrocephalus In Older People
The type of hydrocephalus diagnosed among older people in their sixties or seventies is usually normal pressure hydrocephalus (NPH). In this condition, the accumulation of CSF causes the ventricles to swell. This puts pressure on the brain tissue and can lead to damage or destruction of some areas of the brain. The name, however, is misleading because the CSF pressure could vary from low to high and have repercussions.
NPH symptoms manifest very gradually. A notable symptom is difficulty in walking, followed by deterioration in mental function, memory loss, poor attentiveness, dullness, and incontinence. An enlarged head is not observed in adults.
NPH may develop under the following conditions:
- If you’ve had a serious head injury
- Because of bleeding in the brain or an aneurysm
- Due to meningitis or other infections in the central nervous system
- After brain surgery (craniotomy)
- Existing health conditions such as diabetes, heart disease or high blood cholesterol levels, all of which impact blood flow, may trigger the development of NPH
While hydrocephalus cannot be prevented, knowing its root cause can help you get the right medical attention. Also, know that the risk of hydrocephalus in babies can be diagnosed or even reduced to an extent by ensuring your pregnancy is well monitored by your doctor. In case of adults, follow all screening and vaccination schedules recommended for your age and gender. That will ensure you are protected from any infectious disease that can trigger hydrocephalus.