The fourth ventricle lies between the brainstem and cerebellum. It is continuous with the cerebral aqueduct rostrally and the central canal of the spinal cord caudally. The floor contains cranial nerve nuclei and is divided by a median sulcus. Cerebrospinal fluid is produced in the ventricles and circulates from the fourth ventricle through openings to the subarachnoid space and is absorbed through arachnoid villi into venous sinuses.

1. 4 th VENTRICLE OF BRAIN
DR SAMEEP KOSHTI

4. •ANATOMY
• The fourth ventricle lies between the brainstem and the cerebellum
• Rostrally,
• continuous with the cerebral aqueduct, and
• caudally
• with the central canal of the spinal cord.
• The ventricle is at its widest
• at the level of the pontomedullary junction,
• where a lateral recess on both sides extends to the lateral border of the brainstem.
• At this point the lateral apertures of the fourth ventricle (foramina of Luschka) open
into the subarachnoid space at the cerebellopontine angle, behind the upper roots of
the glossopharyngeal nerves.

6. • FLOOR OF THE FOURTH VENTRICLE (RHOMBOID FOSSA)
• shallow diamond-shaped or rhomboidal, depression (rhomboid fossa)
• on the dorsal surfaces of the pons and the rostral half of the medulla.
• It consists largely of grey matter and contains important cranial nerve nuclei (V– XII)
• The superior part of the ventricular floor is
• triangular in shape
• and is limited laterally by the superior cerebellar peduncles
• The inferior part of the ventricular floor is also
• triangular in shape and is
• bounded caudally by the gracile and cuneate tubercles.
• More rostrally,
• by the diverging inferior cerebellar peduncles.
• A longitudinal median sulcus divides the floor of the fourth ventricle.

8. • Each half
• is divided, by an often indistinct sulcus limitans, into
• medial region known as the medial eminence and a
• lateral region known as the vestibular area.
• The vestibular nuclei lie beneath the vestibular area.
• In the superior part, the medial eminence is represented
• by the facial colliculus, a small elevation produced by an underlying loop of efferent fibres from the facial
nucleus, which covers the abducens nucleus.
• Between the facial colliculus and the vestibular area the sulcus limitans widens into a small
depression, the superior fovea.
• In its upper part, the sulcus limitans constitutes the lateral limit of the floor of the fourth ventricle.
• Caudal to the facial colliculus,
• at the level of the lateral recess of the ventricle,
• A variable group of nerve fibre fascicles, known as the striae medullaris,
• runs transversely across the ventricular floor and passes into the median sulcus.

9. • In the inferior part,
• the medial eminence is represented by the hypoglossal triangle (trigone), which lies over
the hypoglossal nucleus.
• Laterally, the sulcus limitans widens to produce an indistinct inferior fovea.
• Caudal to the inferior fovea,
• between the hypoglossal triangle and the vestibular area, is the vagal triangle (trigone),
which covers the dorsal motor nucleus of the vagus.
• A narrow translucent ridge, the funiculus separans, which is separated from the gracile
tubercle by the small area postrema, crosses below the vagal triangle.

15. •THE ROOF OF THE FOURTH VENTRICLE
• is formed by the superior and inferior medullary velum.
• The thin superior medullary velum stretches across the ventricle between the converging superior
cerebellar peduncles and is continuous with the cerebellar white matter.
• Dorsally, it is covered by the lingula of the superior vermis.
• The inferior medullary velum is more complex and is mostly composed of a thin sheet,
devoid of neural tissue, formed by ventricular ependyma and the pia mater of the tela
choroidea.
• Just inferior to the nodule of the cerebellum, a median aperture, the foramen of
Magendie, opens the roof of the fourth ventricle into the cisterna magna.
• Applied:
• The aperture forms when a membranous structure (Blake’s pouch) perforates into the fourth ventricle at the
ninth week of fetal development.
• persistence of this membrane results in cystic obstruction of the median outlet from the fourth ventricle

17. CSF CIRCULATION
• Formation:
• the choroid plexuses of the lateral, third, and fourth ventricles;
• Some originates from the ependymal cells lining the ventricles
• from the brain substance through the perivascular spaces.
• Production rate :
• produced continuously at a rate of about 0.5 (0.2-0.7) mL per minute and
• with a total volume of about 150 mL
• this corresponds to a turnover time of about 5 hours.
• The circulation is aided by :
• the arterial pulsations of the choroid plexuses and
• by the cilia on the ependymal cells lining the ventricles.

18. • From the fourth ventricle  the median aperture and the lateral foramina of
the lateral recesses of the fourth ventricle  the subarachnoid space 
cerebellomedullary cistern and pontine cisterns  flows superiorly through the
tentorial notch of the tentorium cerebelli  inferior surface of the cerebrum 
• Some superiorly to lateral aspect of each cerebral hemisphere
• Some inferiorly in the subarachnoid space around the spinal cord and cauda equina.
• Here,the fluid is at a dead end,and its further circulation relies on the pulsations of the
spinal arteries and the movements of the vertebral column, respiration, coughing, and the
changing of the positions of the body.

19. • CSF ABSORPTION:
1. The main sites: arachnoid villi (Together called arachnoid granulations) that project into the
dural venous sinuses, especially the superior sagittal sinus.
• The arachnoid granulations increase in number and size with age and tend to become calcified with advanced
age.
2. into the venous sinuses
• occurs when the cerebrospinal fluid pressure exceeds the venous pressure in the sinus.
• (not true vice versa as Arachnoid villi tubules closes in case of raised venous pressure and act as valves).
3. Some directly into the veins in the subarachnoid space,
4. Some possibly escapes through the perineural lymph vessels of the cranial and spinal nerves.
• Because the production of cerebrospinal fluid from the choroid plexuses is constant,
the rate of absorption of cerebrospinal fluid through the arachnoid villi controls the
cerebrospinal fluid pressure.