Pediatric hydrocephalus

Everyone produces approximately half a litre of CSF per day. The fluid is generated in the choroid plexus within the cerebral ventricles, circulates through the ventricular system and around the brain and spinal cord via the subarachnoid space, and is reabsorbed by arachnoid granulations into the venous sinuses. This continuous cycle maintains a stable, protective environment for the central nervous system.

Hydrocephalus interrupts this cycle. When CSF cannot flow or be reabsorbed normally, it accumulates in the ventricles. Ventricular enlargement compresses the surrounding brain parenchyma and raises intracranial pressure, causing the symptoms described above. In infants, whose skull sutures are still open, the head circumference can increase rapidly; once the sutures fuse, the same fluid accumulation produces a more acute rise in intracranial pressure.

**Causes**

Many cases have no clearly identified cause, but recognised associations include: - *Intraventricular haemorrhage* — the most common cause in premature infants; blood clots obstruct CSF pathways - *Congenital malformations* — aqueductal stenosis (narrowing of the cerebral aqueduct), Chiari malformation, Dandy-Walker syndrome, neural tube defects - *Infection* — bacterial meningitis or intrauterine infection (TORCH) scarring - *Tumours* — a posterior fossa tumour is a common cause of obstructive hydrocephalus in older children - *Vascular anomalies* — vein of Galen malformation - *Genetic* — a small proportion are inherited (X-linked hydrocephalus from L1CAM mutation)

**Diagnosis**

- *Ultrasound* — used in infants with an open fontanelle; fast, non-irradiating, bedside-capable - *MRI* — preferred when possible; provides detail of ventricle size, the CSF pathway obstruction, and brain parenchymal changes; usually requires sedation - *CT* — faster than MRI; useful in emergency presentations or when MRI is unavailable

Serial imaging is used to monitor ventricular size over time and assess whether the hydrocephalus is progressive or stable.

**Prognosis**

Hydrocephalus itself is highly treatable. The outcome for the child depends primarily on the underlying cause and any associated brain injury. Premature infants with post-haemorrhagic hydrocephalus and children with severe congenital anomalies often have additional developmental challenges; isolated aqueductal stenosis treated early typically carries a good prognosis.

**Treatment**

*Ventriculoperitoneal (VP) shunt:* A thin silicone catheter placed from the lateral ventricle under the scalp and down the neck to the peritoneal cavity. A one-way valve prevents backflow. Many modern shunts have magnetically programmable valves that allow non-invasive pressure adjustment. Shunts can fail mechanically (obstruction or disconnection), requiring revision surgery; they can also become infected, most commonly in the first months after implantation.

*Endoscopic third ventriculostomy (ETV):* A small fenestration made in the floor of the third ventricle using an endoscope, allowing CSF to bypass the obstructed aqueduct and enter the subarachnoid space. Avoids implanted hardware; infection risk is lower than shunting. Most effective in older children with obstructive hydrocephalus (aqueductal stenosis); less effective in infants and in communicating hydrocephalus. Can fail over time, requiring conversion to shunting or repeat ETV.

*ETV + choroid plexus cauterisation (ETV-CPC):* In young infants, particularly those with post-infectious hydrocephalus, cauterising the choroid plexus (which produces much of the CSF) in combination with ETV improves success rates compared with ETV alone.