Aqueductal stenosis

Definitions & Key takeaways

The cerebral aqueduct, also referred to as the aqueduct of Sylvius, is a channel that carries cerebrospinal fluid (CSF) from the third to the fourth ventricle. Aqueductal stenosis means that this channel becomes narrow and does not allow CSF to properly flow through. This can lead to the accumulation of CSF in the brain, a condition known as hydrocephalus. As much CSF accumulates, it leads to brain compression and associated symptoms such as headache, vomiting, nausea, changes in mental status, and seizures. Children with hydrocephalus can present with head enlargement, intellectual disability, and developmental delay. The diagnosis is typically made with a CT scan or MRI.

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Introduction0:00–0:21

With aqueductal stenosis, aqueductal refers to a channel in the brain that allows fluid to flow through, and stenosis referring to a narrowing.
So aqueductal stenosis is a problem where a channel in the brain’s ventricular system gets narrowed, and that makes it hard for cerebrospinal fluid to flow through.
Let's start with some relevant anatomy. The brain has four interconnected cavities in the brain called ventricles, and each one contains a structure called a choroid plexus.

Anatomy and physiology0:21–1:22

The choroid plexus is made up of ependymal cells which produce cerebrospinal fluid - a fluid that helps provide buoyancy and protection, as well as metabolic fuel for the brain.
Highest up, are two C-shaped lateral ventricles that lie deep in each cerebral hemisphere. The two lateral ventricles drain their cerebrospinal fluid into the third ventricle, which is a narrow, funnel-shaped, cavity at the center of the brain.
The third ventricle makes a bit more cerebrospinal fluid and then sends all of the cerebrospinal fluid to the fourth ventricle via the cerebral aqueduct.
The fourth ventricle is a tent-shaped cavity located between the brainstem and the cerebellum. After the fourth ventricle, the cerebrospinal fluid enters the subarachnoid space, which is the space between the two inner linings of the brain - the arachnoid and pia mater.

Pathology1:22–2:24

Cerebral aqueduct stenosis develops when there’s a blockage of the cerebral aqueduct between the third and fourth ventricle, and most of the time this blockage is caused by a tumor.
Most often it’s a pineal gland tumor, which sits just dorsal to the aqueduct at the level of the midbrain. Cerebral aqueduct stenosis can also be a congenital problem like if the channel itself is malformed, with lots of abnormal branching that have dead-ends.
Sometimes when there’s forking, cerebrospinal fluid accumulates in these branches, and it causes them to expand and compress the main cerebral aqueduct.
Eventually, if this compressive force closes off the aqueduct it can stop the flow of cerebrospinal fluid completely. Regardless of the cause, when the cerebral aqueduct is shut off, it leads to obstructive hydrocephalus which is where there’s a buildup of cerebrospinal fluid inside the ventricles.
That makes the ventricles dilate and that in turn compresses the surrounding brain tissue. The main symptoms of aqueductal stenosis are related to the brain compression - so that includes headaches, vomiting, seizures, balance disturbances, and visual problems.

Symptoms2:24–2:46

Children with hydrocephalus can have an enlarged head and developmental delays, intellectual disability, and muscle spasticity.

Diagnosis2:46–2:55

The best way to diagnose aqueductal stenosis is with an MRI because it can visualize the entire length of the aqueduct. Treatment for Aqueductal Stenosis typically involves the placement of a shunt, like a ventriculoperitoneal shunt, which connects the ventricular system to the peritoneal cavity in order to allow fluid to drain out and get reabsorbed by the cells lining the peritoneal pleura.

Treatment2:55–3:23

This helps to reduce the intracranial pressure caused by hydrocephalus. In addition, individuals often benefit from physiotherapy to help them develop their motor skills.

Review3:23–3:41

All right, as a quick recap, cerebral aqueduct stenosis is a narrowing of the cerebral aqueduct which blocks the flow of cerebrospinal fluid from the third to fourth ventricle.
It most commonly occurs due to a pineal gland tumor or congenital malformations, and results in obstructive hydrocephalus.