Cerebral aqueduct

The cerebral aqueduct (aqueduct of the midbrain, aqueduct of Sylvius,  sylvian aqueduct, mesencephalic duct) is a narrow   conduit for cerebrospinal fluid (CSF) connecting the third ventricle and fourth ventricle of the ventricular system of the brain. The cerebral aqueduct is a midline structure. It extends rostrocaudally through the entirety of the more dorsal/posterior part of the mesencephalon (midbrain). It is surrounded by a layer of gray matter called the periaqueductal gray (central gray).

Congenital stenosis of the cerebral aqueduct is a cause of congenital hydrocephalus.

It is named for Franciscus Sylvius.

Anatomy
The cerebral aqueduct is roughly circular in transverse section, and measures 1-2 mm in diameter.

It is commonly subdivided into a pars anterior antrum, and pars posterior.

Relations
Rostrally/superiorly, it is continuous with the third ventricle, commencing just inferior to the posterior commissure.

Caudally/inferiorly, it is continuous with the fourth ventricle at the junction of the mesencephalon and pons.

The tegmentum mesencephali is situated ventrally/anteriorly to the cerebral aqueduct; The portion of the tegmentum dorsal to the aqueduct is the tectum.  The corpora quadrigemina (i.e. the superior and inferior colliculi) are situated dorsally/posteriorly to it.

Development
The cerebral aqueduct, as other parts of the ventricular system of the brain, develops from the central canal of the neural tube, and it originates from the portion of the neural tube that is present in the developing mesencephalon, hence the name "mesencephalic duct."

Function
The cerebral aqueduct acts like a canal that passes through the midbrain. It connects the third ventricle with the fourth ventricle so that cerebrospinal fluid (CSF) moves between the cerebral ventricles and the canal connecting these ventricles.

Clinical significance
Aqueductal stenosis, a narrowing of the cerebral aqueduct, obstructs the flow of CSF and has been associated with non-communicating hydrocephalus. Such narrowing can be congenital, arise via tumor compression (e.g. pinealoblastoma), or through cyclical gliosis secondary to an initial partial obstruction.

History
The cerebral aqueduct was first named after Franciscus Sylvius.