VENRTICLES OF BRAIN – ANATOMY, INTERCONNECTIONS AND SIGNIFICANCE

The ventricles of brain are interconnected cavities within brain containing cerebrospinal fluid.

There are four ventricles in brain :

• Two lateral ventricles – one in each cerebral hemisphere
• One third ventricle – in diencephalon
• One fourth ventricle – in hindbrain

The lateral ventricles communicate with the third ventricle through interventricular foramina of Monro. The third ventricle communicates with fourth ventricle through the cerebral aqueduct. The fourth ventricle is connected with the central canal of the spinal cord. The fourth ventricle communicates with the subarachnoid space through its median foramen of Magendie and paired lateral foramina of Luschka. The cerebrospinal fluid passes through foramen of Magendie and foramina of Luschka into the sub arachnoid space.

Ventricles of brain possess choroid plexus which is a vascular plexus of piamater that secretes cerebrospinal fluid.

LATERAL VENTRICLE

Lateral ventricle is the cavity of cerebrum. They are two in number, one in each cerebral hemisphere. Each lateral ventricle is C shaped in architecture. The interventricular foramina of Monro forms the connection between lateral ventricles and the third ventricle. The two lateral ventricles are separated from each other by septum pellucidum.

PARTS OF LATERAL VENTRICLE

Each lateral ventricle consists of :

• BODY / CENTRAL PART – in parietal lobe
• ANTERIOR HORN – in frontal lobe
• POSTERIOR HORN – in occipital lobe
• INFERIOR HORN – in temporal lobe

ANTERIOR HORN (FRONTAL HORN)

The anterior horn lies in the frontal lobe of cerebrum in front of the interventricular foramen. Beyond the interventricular foramen, it becomes continuous with the body of lateral ventricle.

Its transverse section shows a triangular shape. It has a medial wall. roof, floor and an anterior wall.

MEDIAL WALL – Formed by septum pellucidum.

ROOF – Formed by lower surface of body of corpus callosum (anterior part).

FLOOR – Has head of caudate nucleus laterally and upper surface of rostrum of corpus callosum medially.

ANTERIOR WALL – Formed by genu of corpus callosum.

CENTRAL PART (BODY)

The body of lateral ventricle extends from interventricular foramen to the splenium of corpus callosum. Then it splits into inferior and posterior horns. It is located in the parietal lobe.

It is triangular in transverse section. It consists of a medial wall, a roof and a floor.

MEDIAL WALL – Formed by septum pellucidum.

ROOF – Formed by lower surface of body of corpus callosum.

FLOOR – Has following structures from lateral to medial side – body of caudate nucleus, groove between caudate nucleus and thalamus containing thalamo-striate vein medially and stria terminalis laterally, upper surface of thalamus (lateral part) and body of fornix (lateral edge).

POSTERIOR HORN (OCCIPITAL HORN)

The posterior horn lies in the occipital lobe behind the splenium of corpus callosum. Its transverse section is triangular in shape. It has a medial wall, roof and lateral wall.

MEDIAL WALL – Shows two elevations, bulb of posterior horn above ( formed by fibers of splenium of corpus callosum) and calcar avis below (formed by calcarine sulcus).

LATERAL WALL AND ROOF – Formed by tapetum of corpus callosum.

INFERIOR HORN (TEMPORAL HORN)

It is located in the temporal lobe and is the largest horn. It has a roof and a floor.

ROOF – Formed by central white matter of temporal lobe, tapetum and stria terminalis medially and tail of caudate nucleus laterally. Amygdaloid nucleus is present at the anterior end of the roof.

FLOOR – Formed laterally to medially by – collateral eminence of collateral sulcus, hippocampus, fimbria of hippocampus.

THIRD VENTRICLE

Third ventricle is the cavity of diencephalon. It extends from lamina terminalis anteriorly to pineal body posteriorly. Lamina terminalis is a thin sheet of grey matter which extends from optic chiasma to rostrum of corpus callosum.

It has two lateral walls ( right and left ), an anterior wall, a posterior wall, a floor and a roof.

LATERAL WALL – From above downwards, it is made by – medial surface of thalamus, hypothalamic sulcus and hypothalamus.

ANTERIOR WALL – Formed by – lamina terminalis, anterior commissure and anterior pillar of fornix.

FLOOR – From back to forwards it is made by – upper surface of cerebral peduncle, posterior perforated substance, mamillary bodies and tuber cinerium with infundibulum.

POSTERIOR WALL – It is made by – upper end of cerebral aqueduct and stalk of pineal body with pineal recess.

ROOF – From below to above, it is formed by – dorsomedial borders of the two thalami, tela choroidea of third ventricle, body of fornix and body of corpus callosum.

RECESSES OF THIRD VENTRICLE – Optic recess above optic chiasma, infundibular recess behind optic chiasma, pineal recess in pineal stalk, supra pineal recess above pineal body.

FOURTH VENTRICLE

Fourth ventricle is the cavity of hindbrain. It is located between the pons and upper half of medulla oblongata in front and the cerebellum behind. Inferiorly, it is continuous with the central canal of spinal cord. Its upper part communicates with the third ventricle via cerebral aqueduct.

It has a roof, a floor and two lateral walls (right and left).

FLOOR – The floor of fourth ventricle is called rhomboid fossa. It is diamond shaped. Upper part of the floor is formed by pons and lower half by medulla oblongata. It is divided into right and left halves by a median sulcus. There are two small depressions called superior fovea and inferior fovea on each side. Sulcus limitans joins superior and inferior fovea. Sulcus limitans thus divides each half into a medial and a lateral area. Motor nuclei lie in medial area and sensory nuclei are situated in the lateral area.

Floor of fourth ventricle can be sub divided into – upper, middle and lower parts.

Upper part of floor – This part shows an elevation called facial colliculus which overlies the internal genu of facial nerve and abducent nerve nucleus. A small bluish area called locus coeruleus is present a little above and lateral to facial colliculus. Nucleus coeruleus lies deep to locus coeruleus.

Lower part of floor – Two triangles can be seen in this part. Hypoglossal triangle is present medially which overlies hypoglossal nucleus. Laterally, there is vagal triangle, which overlies dorsal nucleus of vagus nerve. Laterally and posteriorly to vagal triangle is area postrema. A ridge named funiculus separans separates vagal triangle and area postrema.

Middle part of floor – Consists of vestibular area situated lateral to both fovea and overlying the vestibular nuclei. Stria medullares are thin nerve fiber strands which run from median sulcus to lateral recess.

LATERAL WALL – Its upper part is formed by superior cerebellar peduncles. The lower part is made by gracile tubercle, cuneate tubercle and inferior cerebellar peduncle.

ROOF – It is tent shaped in sagittal section and projects into cerebellum. Upper part of roof is formed by superior cerebellar peduncles and superior medullary velum. Middle part is made by anterior cerebellar notch and lower part by inferior medullary velum. The median aperture of Magendie is present in lower part of roof.

FUNCTIONS OF VENTRICLES OF BRAIN

• The choroid plexus within the ventricles is responsible for producing cerebrospinal fluid which surrounds brain and spinal cord.
• Ventricles provide buoyancy to brain so that it can float inside the skull. This reduces the effective weight of brain.
• They act as cushion to protect brain from physical harm.
• The cerebrospinal fluid removes wastes from central nervous system and transports nutrients to it.

CLINICAL SIGNIFICANCE OF VENTRICLES

Obstruction to the flow of cerebrospinal fluid may occur if there is occlusion of interventricular foramen, cerebral aqueduct, median aperture of Magendie or lateral foramina of Luschka. This will result in hydrocephalus, which is an abnormal increase in cerebrospinal fluid inside the skull.