The Fourth Ventricle

The Fourth Ventricle

Introduction: -last and lowest ventricles of cerebrum.-tent shaped roof which contains 3 apertures for the release of closely guarded CSF into subarachnoid space for absorbtion into SSS. -is also called cavity of hindbrainis tent shaped space situated between pons & medulla in front and cerebellum behind.

Communication: -Superiorly: communicates with third ventricle through cerebral aqueduct. -inferiorly: continuous with central canal of medulla, and of spine -dorsally: in lower part of roof there is median aperture( foramina of Magendie)-through this ventricle communicates with cisterna magna. -on either side: communicates with subarachnoid space through two lateral apertures( foramina Luskcha)

Recesses of the 4th ventricle -median dorsal recess, extends into white core of cerebellum above nodule -two lateral dorsal recesses, one on each side extends backward, lying above inferior medullary velum and below cerebellar nuclei.

-each lateral recess laterally between inf. Cerebellar peduncle ( in front) and stem of flocculus(behind). Each recess opens at its lateral end through foramen of Lusckha.

Lateral boundaries: -4th ventricle is bounded by inferolaterally, by gracile tubercle, fasciculus cuneatus, cuneate tubercle and inferior cerebellar peduncle. superolaterally, by superior cerebellar peducle.

Roof of 4th ventricle -tent shaped projecting into cerebellum formed by: superior cerebellar peduncles, superior medullary velum, tela choroidea of 4th ventricle containing choroid plexus and Taenia with obex -taenia are white ependymal ridges covered with tela choriodea lying along inferolateral margins of rooftwo taeniae are continuous below with obex which covers the inf. angle of ventricle.

-choroid plexus of fourth ventricle is supplied by a branch from post. Inf. Cerebellar artery- lies within tela choroidea of 4th ventricleentire plexus is T shaped or vertical limb of T being double- foramen of Magendie lies between two limbshorizontal limbs extend into lateral recesses and protrude through foramina of Luschka in subarachnoid space.

Floor of fourth Ventricle -also called rhomboid fossa. -floor is formed by post. Surface of pons and post. Surface of open part of medulla. -deep to the floor layer of grey matter containing various cranial nerve nuc. are seen. -lined by ependyma

Followings are seen in the Floor: -median sulcus divides floor into right & left halves. -on either side of midline there is an elevation called median eminence. bounded laterally by sulcus limitans. Followings are seen in relation to sulcus limitans. -bluish coloured area called locus coeruleus, deep to which is substantia ferruginea. -depression, sup. fovea which lies just lateral to facial colliculus -another depression, inf. fovea lies just above vagal triangle.

Followings features are seen in relations to median eminence -facial colliculus is an elavation over upper part of medial eminence.- produced by underlying abducent nuc and fibers of facial nerve as they wind around abducent nuc. -in the lower part of eminence hypoglossal triangle lodges hypoglossal nucleus. Vestibular area lies lateral to fovea-parts of it extends into lateral recess and forms an elevation called auditory tubercle. It overlies dorsal cochlear nucleus and cochlear nerve.

Striae medullaris are transverse lines running across floor.pass fibers from arcuate nucleus to opposite half of cerebellum Vagal triangle lies below inferior fovea & between hypoglossal triangle and vestibular area – over lies the dorsal nucleus of vagus nerve.

Clinical Anatomy a) Infratentorial brain tumours block the median and lateral foramina situated in the roof of the ventricle. This results in marked and early rise if intracranial pressure due to hydrocephalus.