Fourth ventricle
The fourth ventricle is one of the components of the ventricular system in the brain, along with the lateral and third ventricles. It extends from the cerebral aqueduct (of Sylvius) to the obex and is filled with CSF.
CSF enters the ventricle via the cerebral aqueduct and leaves via one of four routes:
- via the obex and into the central spinal canal
- via the median aperture (of Magendie) into the cisterna magna
- via ones of the two lateral apertures (of Luschka) into the quadrigeminal cistern
It is characteristically diamond-shaped in cross-section and located within the pons or upper part of the medulla oblongata. The "roof" (dorsally) is formed by the cerebellum and the "floor" (ventrally), by the rhomboid fossa. The side "walls" are formed by the cerebral peduncles.
The obex is the most caudal tip of the fourth ventricle.
