What Is Hydrocephalus?
The term hydrocephalus comes from the Greek words "hydro" (water) and "cephalus" (head). Historically, it was referred to as "water on the brain." In reality, this "water" is cerebrospinal fluid (CSF)—a clear fluid that surrounds the brain and spinal cord.
CSF is continuously produced in the brain's ventricles. It flows through a network of channels, bathes the brain and spinal cord, and is eventually absorbed into the bloodstream. Hydrocephalus occurs when there is an imbalance between the amount of CSF that is produced and the rate at which it is absorbed, leading to a buildup of fluid that expands the ventricles and puts pressure on the brain tissue.
Cerebrospinal fluid isn't just "extra water." It acts as a shock absorber to protect the brain, delivers nutrients to the brain and spinal cord, and flushes away waste products from the brain's metabolic processes.
Types and Causes
Hydrocephalus is generally classified based on where the CSF blockage occurs and the patient's age at onset.
Occurs when the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles. Common causes include brain tumors, cysts, or aqueductal stenosis (a narrowing of the aqueduct of Sylvius).
Occurs when the flow of CSF is blocked after it exits the ventricles. The fluid can still flow between the ventricles, but it cannot be absorbed properly into the bloodstream. This often happens after a subarachnoid hemorrhage, meningitis, or head trauma.
A specific form of communicating hydrocephalus that primarily affects the elderly. In NPH, the ventricles enlarge, but the pressure of the CSF remains mostly normal. It is frequently misdiagnosed as Alzheimer's or Parkinson's disease due to similar symptoms.
Symptoms by Age Group
Because the skull of an infant is flexible, the symptoms of hydrocephalus look vastly different in babies compared to older children and adults whose skulls are rigidly fused.
An unusually large head, a rapid increase in head size, a bulging "soft spot" (fontanelle) on the top of the head, vomiting, sleepiness, and eyes that look downward ("sunsetting" eyes).
Severe headaches, nausea, blurred or double vision, balance/coordination problems, lethargy, and a decline in academic or work performance. In acute cases, it can cause rapid coma.
Often presents with the classic "Hakim's triad": magnetic or shuffling gait (difficulty walking), mild dementia/memory loss, and a loss of bladder control (incontinence).
Normal Pressure Hydrocephalus is one of the few reversible causes of dementia. If an older adult develops walking difficulties followed by memory issues and incontinence, an evaluation for NPH is critical before assuming it is Alzheimer's disease.
Diagnosis & Imaging
A diagnosis is made through a combination of a neurological exam and brain imaging techniques to visualize the enlarged ventricles and determine the cause of the blockage.
- 1
CT Scan of the Brain - Often the first test performed in an emergency room. It provides a rapid image showing if the ventricles are enlarged.
- 2
MRI of the Brain - Provides highly detailed images. It is essential for determining the underlying cause, such as finding a tumor, cyst, or aqueductal stenosis blocking the fluid.
- 3
High-Volume Lumbar Puncture - For suspected NPH, a large amount of spinal fluid may be drained via a spinal tap. If the patient's walking dramatically improves afterward, it is a strong indicator they will respond well to shunt surgery.
- 4
ICP Monitoring - In complex cases, a small monitor may be placed through the skull to directly measure Intracranial Pressure over 24-48 hours.
Treatment: Shunt Surgery
The most common treatment for hydrocephalus is the surgical insertion of a drainage system called a shunt. A shunt diverts the excess CSF from the brain to another part of the body (usually the abdomen) where it can be naturally absorbed.
A soft, flexible tube inserted through a small hole in the skull directly into the enlarged brain ventricle to gather fluid.
A one-way valve controls the flow rate. Many modern valves are "programmable," meaning the neurosurgeon can adjust the drainage pressure externally using a magnet.
The tube is tunneled just under the skin behind the ear, down the neck, and usually into the peritoneal cavity of the abdomen (a Ventriculoperitoneal or "VP" shunt).
If you have a programmable shunt valve, strong magnetic fields like those in an MRI machine can accidentally change your valve setting. Always inform technicians you have a programmable shunt, and have your neurosurgeon check the setting after any MRI.
Treatment: Endoscopic Third Ventriculostomy (ETV)
For certain types of hydrocephalus, an alternative to a shunt is Endoscopic Third Ventriculostomy (ETV). In this minimally invasive procedure, a neurosurgeon uses a tiny camera (endoscope) to navigate inside the brain's ventricles.
The surgeon creates a small hole in the floor of the third ventricle, bypassing the blockage and allowing the CSF to flow freely around the brain where it can be absorbed naturally. This procedure avoids the need for permanent hardware (a shunt) to be left in the body.
ETV is most successful in patients with obstructive hydrocephalus (such as aqueductal stenosis or certain brain tumors). It is generally less effective for communicating hydrocephalus or older adults with NPH, where a VP shunt remains the gold standard.
Shunt Complications & Warning Signs
While shunts are life-saving, they are mechanical devices and can fail over time. Patients and families must recognize the warning signs of a shunt malfunction or infection.
| Complication | What Happens | Action Required |
|---|---|---|
| Shunt Malfunction (Blockage) | The catheter becomes blocked by tissue or blood, causing pressure to rise again. Symptoms mirror original hydrocephalus symptoms. | Surgical revision to replace the blocked part of the shunt. |
| Shunt Infection | Usually occurs within 1-6 months post-surgery. Causes fever, redness along the shunt tract, and neck stiffness. | Immediate antibiotics, removal of the infected shunt, and a temporary external drain. |
| Over-drainage | The shunt drains too much fluid too quickly, causing the brain to pull away from the skull, potentially leading to subdural hematomas. | Reprogramming the valve to a higher pressure setting, or surgical intervention if severe. |
For anyone with a shunt: severe recurring headaches accompanied by vomiting, extreme lethargy, or visual changes are considered a shunt malfunction until proven otherwise. Seek immediate emergency room evaluation.
Questions to Ask Your Neurosurgeon
- 1
What type of hydrocephalus do I (or my child) have? - This determines whether an ETV or a shunt is the best option.
- 2
Am I a candidate for an ETV instead of a shunt? - ETV avoids foreign hardware, but it is only suitable for specific anatomical blockages.
- 3
If I need a shunt, will it have a programmable valve? - Programmable valves allow adjustments without additional surgery, which is highly beneficial.
- 4
What are the exact signs of a shunt malfunction I should watch for? - The symptoms can differ slightly from person to person.
- 5
(For Seniors) How can we be sure this is NPH and not Alzheimer's? - Ask about a high-volume lumbar puncture trial to test for symptom reversibility.
- 6
How often will I need follow-up imaging (CT/MRI)? - Most patients require regular follow-ups to ensure the ventricles remain stable.
Watch: Hydrocephalus Shunts and ETV Explained
Use this video section for patient-friendly explanations of CSF flow, the differences between shunts and ETV, and what to expect during surgery.
Watch on YouTube →
