Hydrocephalus: Causes, Symptoms, Diagnosis, and Treatment

What is Hydrocephalus?

The brain and spinal cord are housed within a rigid bony compartment formed by the skull and the vertebral canal. This evolutionary design provides exceptional protection against mechanical trauma. However, it has a critical limitation: the compartment is fixed and inextensible, so any increase in the volume of its contents will inevitably raise intracranial pressure (ICP).

The three main causes of increased intracranial pressure are:

1. Cerebral edema: Excess fluid accumulating within brain tissue, resulting from increased vascular permeability or damage to central nervous system cells
2. Space-occupying lesions: Including tumors, abscesses, or hematomas (blood collections) that physically expand within the skull
3. Hydrocephalus: An abnormal increase in the quantity of cerebrospinal fluid (CSF) within the brain

---

Cerebrospinal Fluid Circulation and Types of Hydrocephalus

Cerebrospinal fluid (CSF), commonly called liquor in European medical terminology, is a clear, colorless fluid. It is produced primarily by the four choroid plexuses located within the brain’s ventricular system. The choroid plexus is a highly specialized network of blood capillaries and epithelial cells found inside the cerebral ventricles.

Once secreted, CSF circulates through a dynamic, closed circuit:

1. Produced in the lateral and third ventricles
2. Flows through the cerebral aqueduct (of Sylvius) into the fourth ventricle
3. Exits into the subarachnoid space (the space between the two deep meningeal layers: the arachnoid mater and the pia mater), surrounding both the brain and spinal cord
4. Is reabsorbed into the venous system primarily through specialized structures called arachnoid villi (granulations), which project into the large venous sinuses of the skull

Key functions of CSF:

• Mechanical protection: Acts as a hydraulic cushion, absorbing physical shocks and protecting the delicate brain tissue from impact with the skull walls
• Immunological protection: Contains immune cells and factors that help protect the central nervous system from infection
• Metabolic support: Transports nutrients to brain tissue and removes metabolic waste products
• Regulation of cerebral blood flow: Contributes to maintaining stable intracranial pressure

Classification of Hydrocephalus

Hydrocephalus is defined as an abnormal accumulation of CSF leading to dilatation of the ventricular system. It is classified in two main ways:

By Mechanism (Pathophysiology)

By Onset Speed

---

Causes

Hydrocephalus can result from a wide variety of congenital and acquired conditions.

Congenital Causes (Present at Birth)

• Arnold-Chiari malformation: Downward displacement of cerebellar tissue through the foramen magnum, obstructing CSF flow.
• Aqueductal stenosis: Narrowing or blockage of the cerebral aqueduct of Sylvius. This condition is the most common cause of congenital obstructive hydrocephalus.
• Spina bifida (particularly myelomeningocele): Incomplete closure of the neural tube affecting both the spine and CSF dynamics.
• Dandy-Walker syndrome: Malformation of the fourth ventricle and cerebellum impairing CSF circulation.
• Fetal infections: Congenital infections such as rubella, toxoplasmosis, and herpes virus during pregnancy can cause brain inflammation and disruption of CSF pathways.

Acquired Causes (Developing After Birth)

• Meningitis: Inflammation and scarring of the meninges can block CSF absorption through the arachnoid villi
• Brain tumors: Can obstruct CSF pathways directly or through mass effect
• Head trauma: Bleeding or swelling can disrupt normal CSF flow and absorption
• Intraventricular hemorrhage: Particularly common in premature newborns; blood products can obstruct CSF drainage
• Subarachnoid hemorrhage: Blood in the subarachnoid space can impair CSF reabsorption
• Choroid plexus hyperplasia or papilloma: Cause excessive CSF production
• Brain herniation: Displacement of brain tissue that mechanically compresses CSF pathways

Idiopathic Hydrocephalus

In some cases, especially in normal pressure hydrocephalus among the elderly, no identifiable cause can be found. These are termed idiopathic.

---

Signs and Symptoms

The clinical presentation of hydrocephalus depends critically on the patient’s age, as the structural characteristics of the skull differ fundamentally between newborns and adults.

Symptoms in Newborns and Infants

In newborns, the bones of the skull are not yet fused. Instead, they are joined by flexible fibrous membranes called fontanelles and sutures. This means the skull can expand in response to rising intracranial pressure. The most characteristic sign is therefore:

• Abnormally large or rapidly increasing head circumference (macrocephaly)
• Bulging fontanelles: The soft spots on the baby’s head feel tense and full instead of soft.
• Prominent scalp veins.
• Downward deviation of the eyes (“sunset sign”: the eyes appear to gaze downward, with the white of the eye visible above the iris)

Additional symptoms in infants include:

• Seizures / epileptic episodes
• Irritability and inconsolable crying
• Excessive sleepiness / lethargy
• Vomiting
• Poor feeding and weight loss
• Papilledema (swelling of the optic disc) with consequent visual deficits
• Delayed achievement of developmental milestones (cognitive, motor)
• Difficulty walking or abnormal gait (in older infants)

Symptoms in Older Children and Adults

In adults and older children whose skull sutures are fully fused, the skull cannot expand to accommodate increased CSF volume. Pressure therefore builds directly against brain tissue, causing:

• Gait disturbances, which involve abnormal or unsteady walking, can indicate underlying health issues.
• Mood changes and behavioral alterations.
• Headache, which is usually worse in the morning and when changing positions. This happens because of CSF pressure fluctuations during sleep.
• Excessive sleepiness and drowsiness
• Fever (in cases with infectious etiology)
• Fecal incontinence
• Dementia or progressive cognitive decline
• Muscle spasms or spasticity
• Symptoms resembling Parkinson’s disease (rigidity, bradykinesia, shuffling gait)
• Visual disturbances (blurred or double vision from pressure on optic pathways)
• Nausea and vomiting (from brainstem compression)

Normal Pressure Hydrocephalus

Normal Pressure Hydrocephalus (NPH) is a specific and clinically important subtype of chronic hydrocephalus that occurs most commonly in adults over 60 years of age. It is characterized by:

• Ventricular enlargement visible on imaging.
• Normal or near-normal intracranial pressure on lumbar puncture.
• The classic clinical triad (sometimes called Hakim’s triad):
  1. Gait disturbance: A characteristic shuffling, broad-based, slow gait, sometimes described as “magnetic” because the feet seem stuck to the floor.
  2. Cognitive impairment / dementia: Progressive memory loss, slowed thinking, and executive dysfunction.
  3. Urinary incontinence: Loss of bladder control, typically with urgency.

NPH sometimes develops following a neurological event such as stroke, head trauma, or meningitis, but in most cases the cause remains unknown (idiopathic NPH). It is frequently underdiagnosed because its symptoms can be mistaken for Alzheimer’s disease or Parkinson’s disease, as it shares some clinical features with these conditions.

The critical distinction is that NPH is potentially treatable with CSF drainage via shunt placement, making accurate diagnosis particularly important.

---

Complications

The long-term complications of hydrocephalus are variable and difficult to predict, but are generally influenced by:

• The underlying cause of the hydrocephalus.
• The severity of initial symptoms and the degree of intracranial pressure elevation.
• The timeliness of diagnosis: delays increase the risk of irreversible damage.
• The appropriateness and effectiveness of treatment.

In Newborns and Infants

Untreated or late-treated hydrocephalus can cause:

• Significant intellectual disability
• Developmental delays (motor, cognitive, and speech)
• Physical disabilities including visual impairment and epilepsy
• In severe cases, death from brainstem compression

However, with prompt and appropriate treatment, some infants achieve an excellent prognosis with normal or near-normal development.

In Adults

Adults who develop significant memory impairment or other marked cognitive deficits alongside hydrocephalus tend to retain permanent neurological damage, even after treatment. The extent of recoverable function depends on how long the brain was subjected to elevated pressure before intervention.

The principle of time-critical intervention applies: the sooner hydrocephalus is identified and treated, the better the neurological outcome.

---

Diagnosis

Prenatal Diagnosis

Congenital hydrocephalus can often be identified before birth through routine prenatal ultrasound, especially during the second-trimester morphological ultrasound scan. Detection of enlarged cerebral ventricles prompts further evaluation and specialized obstetric and neurosurgical consultation.

Postnatal Clinical Assessment

In older children and adults, the diagnostic workup begins with a neurological examination to assess:

• Reflexes
• Muscle tone and strength
• Sensory function
• Coordination and gait
• Cognitive function (orientation, memory, attention)

Neuroimaging Studies

Imaging is the cornerstone of hydrocephalus diagnosis:

Magnetic Resonance Imaging (MRI) The most detailed and informative imaging modality. MRI:

• Confirms the diagnosis of hydrocephalus.
• Identifies the site and nature of any obstruction.
• Evaluates associated brain abnormalities.
• Does not use ionizing radiation, since it relies on magnetic fields and radio waves instead. This makes it particularly safe for repeated use and in pediatric patients.

CT Scan (Computed Tomography) Faster than MRI and widely available. CT is particularly valuable in emergency settings (acute hydrocephalus) when rapid assessment is critical. Together with MRI, it is the primary imaging tool for diagnosing hydrocephalus.

Cerebral Ultrasound Used primarily in newborns, whose open fontanelles provide an acoustic window through which ultrasound waves can image the brain. It is completely non-invasive, involves no radiation, and can be performed at the bedside. This makes it ideal for monitoring ventricular size in neonatal intensive care settings.

Angiography (Arteriography) An invasive procedure using a catheter inserted into a peripheral vessel (typically at the groin) and advanced to the cerebral circulation, where contrast medium is injected and X-ray images are acquired. Used selectively when vascular causes of hydrocephalus are suspected.

Lumbar Puncture (Spinal Tap / Rachicentesis) A small amount of CSF is withdrawn using a needle inserted between the 4th and 5th lumbar vertebrae. This allows:

• Measurement of CSF opening pressure.
• CSF analysis (cell count, protein, glucose, and culture) to rule out infection.
• In NPH: assessment of symptom response to large-volume CSF drainage (the tap test; a positive response suggests the patient will benefit from shunting).

---

Treatment

Hydrocephalus requires prompt treatment to prevent irreversible brain damage or death. Treatment is surgical in nature and aims to restore normal intracranial pressure by reducing the excess CSF burden. The specific approach depends on the type, cause, and severity of hydrocephalus.

1. CSF Shunt Placement (Ventriculoperitoneal Shunt, or VP Shunt)

The most common and widely used surgical treatment. A small, flexible tube called a shunt is implanted to connect a cerebral ventricle to another body cavity. Typically, this is the peritoneal cavity of the abdomen (a ventriculoperitoneal shunt). However, the pleural cavity around the lungs or the right atrium of the heart may also serve as connection points.

How it works: The shunt contains a pressure-sensitive valve that opens when intracranial pressure exceeds a set threshold, allowing excess CSF to drain out of the ventricles and be safely absorbed by the peritoneum.

Advantages:

• Technically straightforward and well-established
• Effective for most types of hydrocephalus
• Can be programmable (valve pressure adjustable non-invasively with a magnet in some modern designs)

Potential complications:

• Shunt malfunction (obstruction, breakage, or disconnection) may require revision surgery.
• Shunt infection (bacterial colonization of the catheter).
• Over-drainage: This occurs when CSF drains too aggressively. It can lead to low-pressure headaches or even subdural hematomas.
• The shunt requires lifelong monitoring and may need revision as the patient grows (in children).

2. Endoscopic Third Ventriculostomy (ETV)

An increasingly preferred alternative to shunting for obstructive hydrocephalus, particularly when a tumor or other structural blockage prevents normal CSF flow.

A neurosurgeon uses a thin endoscope (camera-equipped surgical instrument) to create a small opening in the floor of the third ventricle, allowing CSF to bypass the obstruction and reach the subarachnoid space where it can be normally absorbed.

Advantages over shunting:

• No implanted foreign material (no hardware to malfunction or become infected).
• More physiological, as it restores a natural CSF pathway.
• Single procedure with no need for lifelong hardware monitoring.

Limitations:

• Not suitable for all types of hydrocephalus (less effective in communicating hydrocephalus where the problem is absorption rather than flow)
• Carries a small risk of injury to adjacent brain structures during the procedure
• May fail in younger infants (lower long-term success rates compared to older children and adults)

3. Choroid Plexus Cauterization

In cases of hypersecretory hydrocephalus (where the choroid plexuses produce excessive CSF), the plexus tissue can be destroyed using electrical coagulation delivered through an endoscope. This reduces CSF production.

This technique is sometimes combined with endoscopic third ventriculostomy, or ETV with CPC. This approach is especially common in low-income settings, where shunt hardware may not be reliably available, as it offers a way to manage hydrocephalus without implanting foreign material.

Post-Surgical Follow-Up

All patients treated for hydrocephalus require long-term neurological follow-up to:

• Monitor shunt function
• Detect and promptly manage complications
• Assess developmental or cognitive progress (especially in children)
• Adjust treatment as needed (e.g., reprogramming adjustable valves)

Patients and their families should be educated on the warning signs of shunt malfunction or failure. These signs can include sudden headache, nausea, vomiting, deteriorating consciousness, or the return of pre-treatment symptoms. If any of these occur, they should seek emergency medical care immediately.

---

Sources and Bibliography

• Kumar V, Abbas AK, Aster JC. Robbins and Cotran Pathologic Basis of Disease. 10th ed. Philadelphia: Elsevier; 2021.
• Berardelli A, Cruccu G. La Neurologia della Sapienza. Rome: Sapienza University Press.
• Kahle KT, Kulkarni AV, Limbrick DD Jr, Warf BC. Hydrocephalus in children. Lancet. 2016;387(10020):788–799. doi:10.1016/S0140-6736(15)60694-8
• Oi S, Di Rocco C. Proposal of “evolution theory in cerebrospinal fluid dynamics” and minor pathway as cerebrospinal fluid absorption pathway in developing immature brain. Childs Nerv Syst. 2006;22(7):662–669.
• Relkin N, Marmarou A, Klinge P, Bergsneider M, Black PM. Diagnosing Idiopathic Normal-Pressure Hydrocephalus. Neurosurgery. 2005;57(3 Suppl):S4–16.
• Rekate HL. A contemporary definition and classification of hydrocephalus. Semin Pediatr Neurol. 2009;16(1):9–15.
• National Institute of Neurological Disorders and Stroke (NINDS). Hydrocephalus Fact Sheet. Available from: https://www.ninds.nih.gov/health-information/disorders/hydrocephalus
• Hydrocephalus Association. Understanding Hydrocephalus. Available from: https://www.hydroassoc.org
• Williams MA, Malm J. Diagnosis and Treatment of Idiopathic Normal Pressure Hydrocephalus. Continuum (Minneap Minn). 2016;22(2 Dementia):579–599.