Hydrocephalus is a condition where cerebrospinal fluid builds up in the brain’s cavities, creating pressure that can damage brain tissues and affect how the brain works. While this condition can develop at any age, it appears most often in babies and adults over sixty years old. Understanding hydrocephalus helps patients and families make informed decisions about managing this lifelong condition.

Understanding How Common Hydrocephalus Is

Hydrocephalus affects people across all age groups, though some populations face higher risk than others. In the United States, approximately one to two out of every thousand babies are born with this condition, making it a relatively common birth defect.^[1] The numbers can vary significantly depending on where in the world you look. Some regions report rates as low as one case per nine thousand live births, while others see one case per two hundred and fifty-six births. These differences often relate to access to prenatal healthcare, prenatal testing options, and availability of medical interventions.^[2]

The condition doesn’t just affect newborns. Among older adults, particularly those over eighty years old, about six percent develop a specific form called normal pressure hydrocephalus.^[3] This makes hydrocephalus a concern throughout the entire lifespan. The condition can appear suddenly or develop slowly over months or even years, depending on what causes it and how the body responds to the buildup of fluid.

Many cases of hydrocephalus in babies are diagnosed before birth during routine prenatal examinations using ultrasound technology. Early detection allows medical teams to prepare for the baby’s arrival and plan appropriate interventions. However, not all cases are identified prenatally, and some children develop hydrocephalus later in childhood due to infections, injuries, or other medical conditions.

What Causes Hydrocephalus to Develop

The root cause of hydrocephalus involves problems with cerebrospinal fluid, which is a clear liquid that surrounds and protects the brain and spinal cord. Your body produces this fluid every day in structures called the choroid plexus inside the brain’s ventricles, which are hollow spaces within the brain. Normally, this fluid flows through these ventricles, bathes the brain and spinal cord, and then gets reabsorbed into the bloodstream. The body maintains a careful balance, producing about the same amount of fluid it absorbs each day.^[4]

Hydrocephalus develops when something disrupts this balance. The fluid can build up for several reasons. Sometimes the pathways that normally allow fluid to flow become blocked. This might happen because of a tumor pressing on these passages, a narrowing of the connection between ventricles called the aqueduct of Sylvius, or scar tissue forming after bleeding or infection. When fluid cannot flow properly, it backs up in the ventricles, causing them to enlarge and press on surrounding brain tissue.^[5]

Another cause involves problems with fluid absorption. Even when the fluid can flow freely through all the pathways, the body might not be able to reabsorb it properly into the bloodstream. This often happens after bleeding in the brain or infections like meningitis, which is an inflammation of the membranes covering the brain and spinal cord. These events can damage the tiny structures called arachnoid granulations that normally absorb cerebrospinal fluid.^[6]

In rare cases, the body produces too much cerebrospinal fluid. This typically occurs when tumors called choroid plexus papillomas grow in the areas that make the fluid, causing overproduction that overwhelms the body’s ability to absorb it.

For babies born with hydrocephalus, the causes often involve developmental problems that occurred during pregnancy. Conditions like spina bifida, which is a defect in the spinal cord’s development, frequently occur alongside hydrocephalus. Other birth defects affecting the brain and spinal cord, genetic factors, or infections that the mother had during pregnancy can also lead to congenital hydrocephalus.^[7]

Who Faces Higher Risk

Certain groups of people and situations increase the likelihood of developing hydrocephalus. Understanding these risk factors helps with early detection and intervention.

Babies face particular vulnerability when they are born prematurely. Premature infants often experience bleeding inside the brain’s ventricles, called intraventricular hemorrhage. This bleeding can block the normal flow of cerebrospinal fluid or damage the structures that absorb it, leading to what doctors call post-hemorrhagic hydrocephalus.^[8]

Infections affecting the brain or its surrounding membranes significantly increase risk. Bacterial meningitis, which is a serious infection of the membranes covering the brain and spinal cord, can cause inflammation and scarring that interferes with fluid flow and absorption. This risk applies to people of all ages who contract these infections.

Head injuries represent another major risk factor, particularly in industrial countries where trauma is common. When someone experiences a traumatic brain injury, bleeding can occur inside the brain or around its surface. This blood can block fluid pathways or damage absorption mechanisms, potentially causing hydrocephalus to develop weeks or even months after the initial injury.^[9]

Brain tumors of various types can obstruct cerebrospinal fluid flow. Tumors in the posterior part of the brain, which includes the cerebellum and brainstem, commonly cause blockages. Other tumor types that frequently lead to hydrocephalus include those growing from brain tissue itself, tumors near the pituitary gland, and tumors that have spread to the brain from cancer elsewhere in the body.

Elderly adults face increased risk for normal pressure hydrocephalus, though doctors don’t fully understand why this form develops. Previous brain bleeding, such as from a ruptured blood vessel, prior meningitis, or head trauma earlier in life can contribute to developing this condition later in adulthood.^[10]

Recognizing the Signs and Symptoms

The symptoms of hydrocephalus vary dramatically depending on a person’s age and how quickly the fluid buildup occurs. Recognizing these signs early can lead to faster treatment and better outcomes.

In infants, one of the most noticeable signs is an unusually rapid increase in head size. Because babies’ skull bones haven’t fused together yet, the increasing pressure can cause the head to expand. Parents or caregivers might notice the soft spot on top of the baby’s head, called the fontanelle, bulging outward or feeling unusually tense. The scalp veins may become more prominent and visible.^[11]

Babies with hydrocephalus often show behavioral changes. They may become extremely irritable or unusually sleepy and difficult to rouse. Feeding problems are common, with babies refusing to eat or vomiting frequently. Their eyes might fix downward in a characteristic pattern doctors call “sunsetting,” where the whites of the eyes show above the colored part. Seizures can occur in some infants. Parents might also notice their baby stops reaching developmental milestones they had previously achieved, such as rolling over or responding to sounds.^[12]

Older children and adults experience different symptoms because their skulls can no longer expand. Headaches become a prominent complaint, often severe and persistent. These headaches may worsen in the morning or when lying down, as these positions can increase pressure inside the skull. Vision problems develop frequently, including blurred vision, double vision, or difficulty moving the eyes in certain directions.

Balance and coordination difficulties affect many patients with hydrocephalus. Walking becomes unsteady, movements slow down, and simple motor tasks require more effort. Some people describe feeling as though their feet are stuck to the ground when trying to walk. Nausea and vomiting often accompany the headaches and increased pressure.^[13]

Cognitive and behavioral changes can significantly impact daily life. People may have trouble concentrating, show personality changes, or experience memory problems. School or job performance often declines. In adults with normal pressure hydrocephalus, three symptoms typically appear together: walking difficulties, problems controlling urination, and progressive memory or thinking problems that can resemble dementia.

The speed at which symptoms develop matters greatly. Acute hydrocephalus, where pressure builds rapidly, causes sudden, severe symptoms and represents a medical emergency requiring immediate attention. Chronic hydrocephalus develops more slowly, sometimes over weeks or months, with symptoms gradually worsening over time. Some people with very slow-developing hydrocephalus might not recognize symptoms until the condition has progressed significantly.

Steps to Prevent Hydrocephalus

While not all cases of hydrocephalus can be prevented, certain measures can reduce risk or help with early detection.

Prenatal care plays a crucial role in prevention. Regular prenatal checkups allow doctors to monitor fetal development and identify potential problems early. Taking proper prenatal vitamins, especially those containing folic acid, before and during pregnancy can reduce the risk of neural tube defects like spina bifida, which often occurs with hydrocephalus. Avoiding infections during pregnancy through good hygiene and staying up to date with appropriate vaccinations protects both mother and developing baby.

Protecting against head injuries at any age helps prevent acquired hydrocephalus. Wearing seatbelts in vehicles, using appropriate helmets during sports and recreational activities, and making homes safer to prevent falls all contribute to reducing traumatic brain injuries that could lead to hydrocephalus.

Prompt treatment of infections affecting the brain or its coverings can prevent complications that lead to hydrocephalus. Anyone experiencing symptoms of meningitis, such as severe headache, fever, stiff neck, and sensitivity to light, should seek immediate medical attention. Early antibiotic treatment for bacterial meningitis can prevent the inflammation and scarring that damages fluid absorption mechanisms.

For babies at high risk, such as premature infants, close monitoring in specialized neonatal care units allows early detection of intraventricular hemorrhage and developing hydrocephalus. Medical teams can then intervene before serious complications develop.

Regular medical checkups become important for people with conditions that increase hydrocephalus risk. Those with brain tumors need ongoing monitoring, as do people who have experienced brain hemorrhages or head trauma. Elderly adults showing early signs of balance problems, urinary difficulties, or memory changes should discuss these symptoms with their doctors, as early detection of normal pressure hydrocephalus leads to better treatment outcomes.

How Hydrocephalus Changes Normal Body Functions

Understanding what happens inside the body when hydrocephalus develops helps explain why symptoms occur and why treatment becomes necessary.

The brain sits inside the rigid skull, which creates a fixed space that cannot expand in older children and adults. Normally, this space contains brain tissue, blood vessels, and cerebrospinal fluid in careful balance. The cerebrospinal fluid serves multiple vital functions: it cushions the brain against injury, delivers nutrients to brain cells, carries away waste products, and helps regulate pressure changes that occur with normal body movements and activities.^[14]

When hydrocephalus develops and cerebrospinal fluid accumulates, the ventricles expand to accommodate the extra volume. This expansion takes up space inside the skull, compressing the brain tissue around the ventricles. The white matter of the brain, which contains the nerve fibers connecting different brain regions, becomes particularly vulnerable to this compression. As these connections get squeezed, they cannot transmit signals properly, leading to problems with movement, thinking, and sensory processing.

The increased pressure inside the skull affects blood flow to the brain. When pressure becomes high enough, it can reduce the amount of blood reaching brain cells, depriving them of oxygen and nutrients they need to function properly. This contributes to symptoms like drowsiness, confusion, and if severe enough, can cause lasting brain damage.

Different types of hydrocephalus create pressure problems through different mechanisms. In obstructive hydrocephalus, also called non-communicating hydrocephalus, something physically blocks the flow of cerebrospinal fluid through its normal pathways. The blockage might occur at narrow passages connecting ventricles or where fluid exits the brain’s ventricle system. Fluid backs up behind the blockage, causing the upstream ventricles to swell. The pressure in these enlarged ventricles increases, compressing surrounding brain tissue.^[15]

In communicating hydrocephalus, the fluid can flow freely through all the ventricles and passages, but problems arise with absorption. The structures responsible for returning cerebrospinal fluid to the bloodstream cannot work properly, often because of damage from bleeding or infection. Even though fluid flows normally through the ventricles, it accumulates because the body cannot reabsorb it fast enough.

Normal pressure hydrocephalus presents a puzzling situation where the ventricles enlarge significantly, but pressure measurements taken at any single point in time often appear normal or only slightly elevated. Researchers believe this occurs because pressure fluctuates, with intermittent periods of increased pressure that gradually damage brain tissue over time, even though pressure readings during testing might not capture these peaks. The slow, chronic nature of this condition allows some compensation to occur, which is why pressure doesn’t remain constantly elevated.^[16]

Another type, hydrocephalus ex-vacuo, develops differently. This occurs when brain tissue shrinks due to conditions like stroke, Alzheimer’s disease, or other degenerative brain diseases. As brain tissue dies and atrophies, cerebrospinal fluid fills the empty space left behind. The ventricles enlarge, but this represents replacement of lost brain tissue rather than excess pressure causing damage. Treatment approaches differ for this type because the primary problem is the underlying brain disease rather than fluid buildup.

In infants whose skull bones haven’t yet fused, the pathophysiology includes an additional component. The pressure from accumulating fluid can push the skull bones apart, allowing the head to expand. While this provides some relief from pressure, it doesn’t solve the underlying problem and creates its own complications. The expanding skull can compress brain tissue against the base of the skull, damage developing nerve pathways, and if severe, lead to permanent developmental delays or disabilities.