Congenital Aqueductal Stenosis

What is congenital aqueductal stenosis?

A “blockage” at a critical point in the circulation of cerebrospinal fluid.

The aqueduct of Sylvius is a very narrow channel in the midbrain that connects the third ventricle to the fourth ventricle. When this channel becomes narrowed or obstructed, cerebrospinal fluid (CSF) cannot pass downward and instead accumulates within the two lateral ventricles and the third ventricle. This results in triventricular hydrocephalus.

The stenosis may be congenital, part of a genetic syndrome, caused by a small tumor (tectal glioma), or follow infection or hemorrhage that scars the aqueduct. The consequence is increased intracranial pressure and abnormal ventricular enlargement—particularly dangerous for the developing brain of a child.

How common is it & what are the main causes?

A not uncommon cause of congenital hydrocephalus, with different etiologies depending on age.

Congenital aqueductal stenosis is estimated to occur in approximately 1 in 5,000 births, although reported rates vary depending on diagnostic criteria. In children, the two principal etiologic groups are:

• Congenital/genetic stenosis – may occur in isolation or as part of rare X-linked syndromes (such as Bickers–Adams–Edwards).
• Secondary stenosis – due to small tectal plate tumors (tectal gliomas account for ~6% of surgically treated pediatric brain tumors), inflammation, infection (e.g., meningitis), or hemorrhage leading to scarring of the aqueduct.

The age at which symptoms appear depends on the degree and rate of obstruction—ranging from infants a few months old to older children with an insidious, slowly progressive presentation.

How does it present in infants & older children?

The clinical signs differ before and after closure of the fontanelles and cranial sutures.

In infants and young children (before fontanelle closure):

• rapid increase in head circumference (> 1 cm/week, above the 98th percentile),
• tense and/or bulging anterior fontanelle,
• separation of cranial sutures, frontal bossing,
• irritability or, conversely, lethargy and decreased interaction,
• vomiting, poor feeding, failure to thrive,
• observable ocular movement abnormalities (upward gaze palsy—“setting sun sign,” less commonly sixth nerve palsy).

In older children and adolescents:

• recurrent headaches, often worse in the morning or associated with nausea/vomiting,
• blurred vision, diplopia, headaches with head tilt,
• fatigue, declining school performance, difficulty concentrating,
• gait instability, clumsiness, or balance disturbances,
• on examination, papilledema or mild cranial neuropathies may be present.

Many children with chronic, slowly progressive aqueductal stenosis may appear “nearly well” for extended periods, experiencing only headaches or learning difficulties until more pronounced decompensation occurs. For this reason, clinical suspicion and timely imaging are essential.

What happens inside the brain?

CSF flow is blocked at a single point, causing pressure to build “upstream” from the obstruction.

Cerebrospinal fluid is produced mainly by the choroid plexus in the lateral ventricles, flows into the third ventricle, through the aqueduct of Sylvius, and then into the fourth ventricle and the subarachnoid space surrounding the brain and spinal cord, where it is absorbed.

In aqueductal stenosis, flow is impeded at the level of the aqueduct. CSF continues to be produced but cannot progress distally, resulting in:

• dilation of both lateral ventricles and the third ventricle,
• elevation of intracranial pressure,
• compression of adjacent brain structures, particularly the visual pathways, thalamus, and brainstem.

In infants, the skull can partially “accommodate” pressure by expanding, so symptoms may initially be milder. In older children, where cranial sutures are fused, pressure rises more rapidly, leading to headaches, vomiting, and visual disturbances.

How is the diagnosis made & which imaging studies are required?

Diagnosis is based on the integration of clinical findings and advanced neuroimaging.

Depending on the child’s age, different modalities are used:

• Transfontanelle ultrasound in infants—a simple, painless examination that can reveal ventricular enlargement.
• Computed tomography (CT)—demonstrates triventricular hydrocephalus, possible midbrain/tectal involvement, and signs of transependymal CSF flow.
• Magnetic resonance imaging (MRI)—the gold standard. High-resolution T2 sequences (FIESTA, CISS) and cine-flow imaging through the aqueduct help to:
  • confirm stenosis or obstruction,
  • identify tectal gliomas or other lesions,
  • assess the relationship of the basilar artery to the clivus when evaluating candidacy for ETV.

In older children, ophthalmologic evaluation (visual fields, funduscopic examination) may be required to assess for papilledema. Diagnosis is typically straightforward when imaging findings are correlated with the clinical presentation.

When is urgent treatment necessary?

There is a distinction between “planned intervention” and “emergency surgery.”

The need for intervention depends on:

• the severity of hydrocephalus on imaging,
• the rate of head circumference growth in infants,
• the presence of symptoms of raised intracranial pressure (vomiting, headache, lethargy),
• ophthalmologic findings,
• focal neurological deficits.

Immediate/emergency intervention is required when:

• there is lethargy, recurrent vomiting, or rapid clinical deterioration,
• the fontanelle is markedly tense and firm to palpation,
• in adolescents, severe headache with vomiting and papilledema is present.

Planned surgery is considered when the child is relatively stable but head growth is rapid or symptoms are chronic (headaches, learning difficulties) and imaging shows significant hydrocephalus.

Are there conservative or temporary options?

Aqueductal stenosis is a mechanical problem—the definitive solution is surgical, although interim measures may occasionally be required.

There are no medications that can “open” the aqueduct or definitively treat hydrocephalus. In selected cases, the following may be used:

• External ventricular drainage (EVD) in severe decompensation, as a temporary measure until definitive surgery is performed.
• Observation with close clinical follow-up and repeat imaging in mild, stable hydrocephalus without symptoms, particularly when assessing a child’s readiness for ETV or ETV-CPC.

However, in the vast majority of cases, aqueductal stenosis is managed with definitive surgical intervention to protect the developing brain.

What are the main surgical options? (VP shunt, ETV, ETV-CPC)

Technique selection depends on age, anatomy, and overall risk profile.

Three principal strategies are currently used:

• Ventriculoperitoneal shunt (VP shunt)
  The traditional, well-established system for diverting CSF from the lateral ventricles to the abdominal cavity via a narrow catheter and flow-regulating valve.
• Endoscopic third ventriculostomy (ETV)
  Endoscopic creation of a small opening in the floor of the third ventricle, allowing CSF to bypass the obstructed aqueduct and flow freely into the basal cisterns.
• ETV with choroid plexus cauterization (ETV-CPC)
  A combination of ETV with extensive cauterization (> 90%) of the choroid plexus in the lateral ventricles, thereby reducing CSF production and increasing the likelihood of long-term shunt independence, particularly in younger children.

The choice depends on age (very young infants have lower ETV success rates), MRI anatomy, associated anomalies, and team experience. For ETV, we often use the ETV Success Score to provide parents with a quantitative estimate of the likelihood of success.

How is the procedure performed in practice?

Small incisions, endoscopic techniques, and modern materials—delivered safely in a pediatric setting.

VP Shunt

• Small scalp incision and burr hole for insertion of the ventricular catheter.
• Placement of the catheter into the lateral ventricle under neuronavigation, connection to a valve (typically programmable), and subcutaneous tunneling to the abdomen.
• The distal catheter is placed into the peritoneal cavity, where CSF is absorbed.

ETV / ETV-CPC

• Small burr hole (usually frontal) and insertion of a fine endoscope into the lateral ventricle using neuronavigation.
• Advancement through the foramen of Monro into the third ventricle and identification of key anatomical landmarks (mammillary bodies, hypothalamus/tuber cinereum, optic tract).
• Perforation of the third ventricular floor (at the center of the tuber cinereum) with a blunt instrument, followed by dilation using a small balloon.
• Inspection of the space beneath the third ventricle for membranes (e.g., Liliequist membrane) that may require additional fenestration.
• In ETV-CPC, a flexible endoscope is used to carefully cauterize the choroid plexus in the lateral ventricles in > 90% of its extent.

Children typically remain in the hospital for 24–48 hours for observation and are subsequently followed with regular clinical visits and repeat imaging.

What is the prognosis & long-term course?

With appropriate technique selection and close follow-up, most children go on to live normal lives.

Children with aqueductal stenosis who are treated in a timely manner:

• experience resolution of symptoms of elevated intracranial pressure (headache, vomiting, lethargy),
• return to normal head growth and overall physical development,
• can attend school and participate in activities comparable to their peers.

Children with a VP shunt are effectively dependent on shunt function and require lifelong surveillance for potential malfunction or infection. Children with successful ETV or ETV-CPC may avoid permanent shunt dependence but are still considered “hydrocephalic” and require long-term follow-up, as delayed failures have been reported even years later.

Neuropsychological outcomes depend largely on:

• the age at onset of hydrocephalus,
• the timeliness of treatment,
• the presence of additional brain anomalies or syndromes.

What are the risks & potential complications?

Every brain operation carries risk—our goal is to minimize it through experience and meticulous planning.

Potential complications can be categorized as follows:

VP Shunt Complications

• Infection of the shunt system—may require shunt removal, external drainage, and intravenous antibiotics.
• Obstruction or kinking of the catheter—leading to recurrence of hydrocephalus symptoms and often requiring revision.
• Overdrainage—resulting in headaches, subdural hematoma, or hygromas.

ETV / ETV-CPC Complications

• Failure of the stoma or early closure—necessitating repeat ETV or shunt placement.
• Hemorrhage or injury to adjacent structures (brainstem, major vessels)—rare but serious, underscoring the need for extensive experience and precise preoperative imaging.
• In ETV-CPC, risk of focal injury if proper technique is not followed during choroid plexus cauterization.

General complications (wound infection, seizures, anesthetic risks) are fortunately uncommon in experienced pediatric centers. At Neuroknife, we place particular emphasis on infection prevention (perioperative antibiotics, meticulous surgical field preparation, double-gloving techniques) and detailed postoperative monitoring.