How hydrocephalus is diagnosed

The clinical exam

Every diagnosis of hydrocephalus starts with a clinician — a pediatrician, a family doctor, a neurologist, or a neurosurgeon — listening to the story and doing an exam.

The exam looks different by age:

• For babies, the most important measurement is the head circumference, plotted on a growth curve over time. A head that is crossing upward on the curve is one of the strongest early clues. The clinician also checks the fontanelle (soft spot), looks at the eyes, and watches movement and tone.
• For older children, the exam looks at vision, balance, coordination, reflexes, and any changes in mood or school performance.
• For adults, the exam adds careful attention to walking — the speed, the size of steps, the ability to turn — and to memory, attention, and reasoning. In suspected NPH, watching someone walk is one of the most useful parts of the visit.

The exam alone does not confirm hydrocephalus. It tells the clinician whether imaging is needed and what to look for.

Ultrasound — in babies and before birth

Ultrasound uses sound waves to make pictures of the inside of the body. It does not use radiation. For hydrocephalus, ultrasound is most useful in two situations:

• In babies under about a year old, the fontanelle on the top of the head provides a window for the ultrasound to look at the brain. This is called a cranial ultrasound or head ultrasound. It can be done at the bedside, even in a neonatal intensive care unit, and does not require sedation.
• Before birth, hydrocephalus can sometimes be seen on a routine prenatal ultrasound. If the ventricles look enlarged, the next step is often a more detailed fetal MRI to get a clearer picture.

After the fontanelle closes (usually between 9 and 18 months), ultrasound is no longer useful for looking at the brain.

MRI — the most detailed picture

MRI stands for magnetic resonance imaging. It uses strong magnets and radio waves — not radiation — to create detailed pictures of the brain. It is generally the test of choice for diagnosing hydrocephalus in older children and adults, and for understanding the cause.

An MRI of the brain shows:

• The size and shape of the ventricles
• Whether something is physically blocking CSF flow (a tumor, a cyst, scarring)
• How the brain tissue around the ventricles looks
• Whether there are signs of recent or old bleeding or infection

Special types of MRI can also look at CSF in motion. A phase-contrast MRI (sometimes called a CSF flow study or cine MRI) shows whether fluid is moving through the narrow channels of the brain or not. This can help tell the difference between communicating and non-communicating hydrocephalus.

An MRI takes longer than a CT — usually 30 to 60 minutes — and requires the patient to hold still. Young children may need sedation.

CT — fast, but uses radiation

CT stands for computed tomography. It uses X-rays to make cross-sectional pictures of the brain. CT is faster than MRI (it takes only a few minutes) and is easier to do in an emergency, but it does expose the patient to a dose of radiation.

CT is most often used:

• In emergencies, when a quick look at the brain is needed
• To check on a known shunt, when a fast comparison to a previous scan is helpful
• When MRI is not possible — for example, in some patients with non-MRI-safe implants

For people who need many scans over many years — especially children — the cumulative radiation matters. This is part of why our research lab has worked on MRI-safe programmable shunt valves and on ultrasonic ways to check shunt function without imaging.

Lumbar puncture and the NPH tap test

A lumbar puncture (LP), also called a spinal tap, removes a small amount of CSF from the lower back with a thin needle. It can measure the pressure of the CSF and check the fluid itself for signs of infection or bleeding.

In suspected normal pressure hydrocephalus, the lumbar puncture takes on a special role. A clinician removes a larger amount of CSF — typically 30 to 50 milliliters — and then asks the patient to walk and to do thinking tests before and afterward. This is called the tap test or large-volume LP.

The idea is simple: if the symptoms get better after removing some CSF, that is a sign that surgically draining CSF with a shunt may help. The tap test does not work for everyone, and a negative test does not always mean a shunt would not help — but it is a useful piece of evidence in the NPH workup.

Pressure monitoring

In selected cases — usually after a head injury, brain hemorrhage, or surgery — doctors may directly measure the pressure inside the head. This is called intracranial pressure (ICP) monitoring. A thin device is placed through a small hole in the skull, either into one of the ventricles (which can also drain CSF) or into the brain tissue itself.

ICP monitoring is mainly used in hospitals, especially in intensive care units, and is not part of a routine outpatient diagnosis of hydrocephalus.

What happens after a diagnosis

When imaging confirms hydrocephalus, the next step is a referral to a neurosurgeon — for children, ideally a pediatric neurosurgeon. The neurosurgery team reviews the type of hydrocephalus, the suspected cause, the patient's age and health, and what symptoms have been bothering the patient.

Depending on that picture, the recommendation may be:

• To proceed with surgery (most commonly a shunt or ETV)
• To watch and re-image, when the situation is mild or stable
• To treat the underlying cause first (for example, a tumor) and reassess
• For suspected NPH, to do a tap test or a temporary lumbar drain before deciding

Many families and patients find it useful to bring a written list of questions to that first neurosurgery visit. There is no rush in most cases — taking the time to understand the recommendation, and to ask about alternatives, second opinions, and long-term care, is reasonable.

Continue learning