Aqueduct of Sylvius

Where in the brain?
The Aqueduct of Silvius (Aquaeductus Cerebri) is a cerebrospinal fluid-filled canal in the midbrain (mesencephalon). The midbrain is part of the brainstem.


In the left image below you see the ventricles without the brain being imaged. The Aqueduct of Silvius is the red narrow 'tube' here.

In the right image you see the ventricles as they run through the head.



The Aqueduct of Silvius, like a kind of water pipe, connects the third ventricle (yellow in the image) and the fourth ventricle (lilac in the image). Ventricles are also called cerebral cavities or cerebral chambers.
Read more about the function and syndromes of these ventricles/brain cavities/brain chambers.


Aqueduct stenosis

Narrowing of the Aqueduct
When there is a narrowing of the Aqueduct of Silvius, it is called an 'aqueduct stenosis'.
The cerebrospinal fluid that is produced daily (400 to 500 milliliters per day) cannot drain away in the event of a stenosis. An engorgement occurs. This is called hydrocephalus.
The narrowing or stenosis can be congenital (congenital aqueduct stenosis), or caused by a tumor in the brain that compresses the aqueduct. It can also be caused by a cerebral hemorrhage, where the accumulated blood clamps the tube. If no cause can be identified, it is called idiopathic aqueduct stenosis.


Diagnosis and treatment
A brain scan shows that the third and fourth ventricles (brain cavities or chambers) are enlarged and constricted.
An operation can reduce the symptoms. A shunt (drain) is placed through keyhole surgery (ventriculoperitoneal shunt surgery).

A shunt is a connection through which fluid can flow away. In this case, the ventriculoperitional shunt (VP) drains the excess cerebral fluid to the abdomen. This is also called ventriculoperitoneal drainage (VPD).


Read more about the consequences of aqueduct stenosis:


Periaqueductal gray PAG

In the brain stem there is an area with many brain cells surrounding the aqueduct.

This area is called the periaqueductal gray or PAG or the substantia grisea centralis.
The gray matter consists of the cell bodies of brain cells. Gray matter processes information.
The PAG has many connections within the central nervous system, both up and down to the spinal cord.
The PAG controls, among other things, premotor brain cells in the brain stem. The brain stem then controls muscle groups such as the bladder sphincter, so that you can hold urine, and the bladder muscles so that you can urinate.

Other functions of the PAG:

  • response to pain (internal stressor) by releasing the body's own painkillers (endogenous opioids):
    • serotonin
    • dynorphin
    • enkephalin
      There is a distinction between the pain that someone expects and the pain that someone actually experiences. The fact that people can estimate that something may hurt is very protective in everyday life because people may act more cautiously.
  • response to a threat or defense (external stressor)
  • autonomic regulation (outside the will) of blood pressure and heart rate
  • sexual functions.

By BodyParts3D[1] by DBCLS. - Polygon data: BodyParts3D ( Blender ( SheepIt(, CC BY-SA 2.1 jp,