Fourth ventricle

At a glance

English

Fourth ventricle

Latin (TA2)

Ventriculus quartus

System

Brain and spinal cord

Region

Head

Side

Single, on the midline

About the fourth ventricle

The fourth ventricle is the lowest of the brain's fluid-filled cavities. It occupies the hindbrain, with the pons and the upper, open part of the medulla oblongata in front of it and the cerebellum behind it. Above, it narrows into the midbrain's cerebral aqueduct; below, it tapers at the obex into the central canal of the closed medulla and spinal cord. Its floor is a rhomboid, which gives the cavity its diamond outline when seen from behind, while in a sagittal slice it looks like a tent pointing back into the cerebellum.

The roof has two halves. The upper half is the superior medullary velum, a thin plate stretched between the two superior cerebellar peduncles. The lower half is a sheet of ependyma and pia, the inferior medullary velum and tela choroidea, which carries the choroid plexus of the ventricle. The peak where they meet is the fastigium, just below the fastigial nucleus. The sides are bounded by the cerebellar peduncles. Fluid escapes through three openings in the lower roof: a median aperture (of Magendie) into the cisterna magna and two lateral apertures (of Luschka) at the ends of the lateral recesses, near the flocculi.

The floor, the rhomboid fossa, is a map of the cranial nerve nuclei below it. A median sulcus divides it into halves, and on each side the sulcus limitans separates the medial eminence, over motor nuclei, from the vestibular area laterally, over sensory nuclei. In the pontine half the facial colliculus marks where facial nerve fibres loop round the abducens nucleus, and the bluish locus coeruleus may show at the upper end. Thin medullary striae cross the floor at the pontomedullary junction. In the medullary half lie the hypoglossal trigone, the vagal trigone and the area postrema, the vomiting centre, near the obex.

Clinically, the ventricle is a frequent site for tumours in children, such as ependymoma and medulloblastoma, which can block CSF flow and cause hydrocephalus with headache and vomiting. Closure of the outlet foramina has the same effect, as in Dandy-Walker malformation. Pressure on the floor can damage the abducens and facial nuclei, giving facial weakness and a squint.

Function and supply

Function

Receives CSF from the aqueduct, adds its own from the choroid plexus, and releases it through the median and lateral apertures into the subarachnoid space.

Blood supply

Its choroid plexus is supplied by the posterior inferior cerebellar arteries, with a contribution from the anterior inferior cerebellar arteries at the lateral recesses.