Cerebral aqueduct (of Sylvius)

Last revised by Jeremy Jones on 17 Apr 2023

The cerebral aqueduct (of Sylvius) is the structure within the brainstem that connects the third ventricle to the fourth.

The cerebral aqueduct is located within the midbrain, connecting the third and fourth ventricles and surrounded by periaqueductal grey matter (PAG), with the tectum of the midbrain located posteriorly and the tegmentum anteriorly. It is roughly 1-2 mm in diameter, with common descriptions separating it into pars anterior, an antrum and pars posterior.

It is filled with CSF, and its obstruction leads to obstructive hydrocephalus with dilatation of the lateral and third ventricles

Franciscus Sylvius (1614-1672) was a Dutch physician and anatomist, after which the duct of Sylvius and the Sylvian fissure are eponymously named.

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