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Ventricles
 

Ventricles

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    Ventricles Ventricles Presentation Transcript

    • VENTRICLES OF BRAIN & CSF MANISHA UTTAM M.P.T-I (Neuro)
    • VENTRICLES • Ventricles are four fluid filled cavities located with in the brain. These are : Two lateral ventricles. Third ventricle. Fourth ventricle.
    • The central canal in the spinal cord has a small dilatation at its inferior end, referred to as the terminal ventricle. The ventricles are lined by an epithelial layer known as ependyma & are filled with cerebrospinal fluid. The ventricles are developmentally derived from the cavity of the neural tube.
    • LATERAL VENTRICLE These are two irregular cavities situated one in each cerebral hemisphere  Each lateral ventricle consists of:  a central part Three horns, anterior, posterior and inferior
    • THE CENTRAL PART This part of lateral ventricle extends from the interventricular foramen in front to the splenium of the corpus callosum behind. BOUNDARIES ROOF : formed by undersurface of corpus callosum FLOOR : formed (from lateral to medial side) by: a. Body of caudate nucleus b. Stria terminalis c. Thalamostriate vein d. Lateral portion of upper surface of thalamus
    • MEDIAL WALL : Formed by- septum pellucidum and body of fornix
    • Choroid fissure is a space between fornix and upper surface of the thalamus A fold of pia mater, the tela choroidea, invaginates through the fissure & covers part of the thalamus The tela choroidea is common to the two lateral ventricles, and to third ventricle Within each lateral edge of the tela choroidea there are plexuses of blood vessels that constitute choroid plexus . The tela choroidea & other structures forming the walls of the ventricle are lined by ependyma.
    • Choroid fissure  A line along which choroid plexus invaginates into lateral ventricle  It’s a c- shaped slit in medial wall of cerebral hemisphere Starts at interventricular foramen (above and in front) & passes around the thalamus Thus it is present only in relation to the central part and inferior horn of the lateral ventricle
    • Its convex margin is bounded by fornix (body and crus),and concave margin is bounded by the thalamus (superior and posterior surfaces), the tail of the caudate nucleus and the stria terminalis.
    • THE ANTERIOR HORN This part lies in front of interventricular foramen and extends into frontal lobe. It is directed forwards, laterally and downwards BOUNDARIES ANTERIOR : Posterior surface of genu and rostrum of corpus callosum ROOF : Anterior part of trunk of corpus callosum FLOOR : a. Head of the caudate nucleus b. Upper surface of the rostrum of the corpus callosum
    • • MEDIAL : a. Septum pellucidum b. Column of fornix
    • THE POSTERIOR HORN This part lies behind the splenium of corpus callosum and extends into occipital lobe. It is directed backwards and medially BOUNDARIES FLOOR & MEDIAL WALL : shows 2 elevations a) Upper,Bulb of posterior horn raised by forceps major b) lower,Calcar avis raised by anterior part of calcarine sulcus ROOF & LATERAL WALL : Tapetum
    • THE INFERIOR HORN Largest horn of lateral ventricle. It begins at the junction of the central part with the posterior horn of lateral ventricle; and extends into the temporal lobe BOUNDARIES ROOF ( & LATERAL WALL) : a) Chiefly the tapetum b) Tail of caudate nucleus c) Stria terminalis
    • THE INFERIOR HORN
    • FLOOR :  Collateral eminence raised by collateral sulcus  Hippocampus medially  In the inferior horn, the line of ependymal invagination by the choroid plexus ( i.e. the choroid fissure ) lies b/w the stria terminalis and the fimbria.
    • THIRD VENTRICLE THIRD VENTRICLE is a median cleft b/w the two thalami. Developmentally, it represents the cavity of diencephalon The cavity is lined by ependyma
    • COMMUNICATIONS Anterosuperiorly, on each side, it communicates with the lateral ventricle through the interventricular foramen (or foramen of monro) This foramen is bounded anteriorly by the column of fornix, and posteriorly by the tubercle of the thalamus. Posteroinferiorly, in the median plane, it communicates with the fourth ventricle through the cerebral aqueduct.
    • RECESSES Recesses are extensions of the cavity. These are: a) Suprapineal b) Pineal c) Infundibular d) Optic
    • BOUNDARIES ANTERIOR WALL : 1) Lamina terminalis 2) Anterior commissure 3) Anterior columns of fornix POSTERIOR WALL : 1) Pineal body 2) Posterior commissure (in the lower lamina of pineal stalk) 3) Cerebral aqueduct
    • ROOF : It is formed by the ependyma lining the under surface of the tela choroidea of the third ventricle The choroid plexus of the third ventricle projects downwards from the roof FLOOR : formed by hypothalamic structures      Optic chiasma Tubercinerium Infundibulum (pitiutary stalk) Mammilary bodies Posterior perforated substance Tegmentum of the midbrain
    • LATERAL WALL : 1) Medial surface of thalamus (in its posterosuperior wall) 2) Hypothalamus (in its anteroinferior part) 3) The hypothalamus sulcus which separates the thalamus from the hypothalamus. The sulcus extends from the interventricular foramen to the cerebral aqueduct
    • TELA CHOROIDEA OF THE THIRD AND LATERAL VENTRICLES Its a double layered fold of piamater that occupies the interval b/w splenium of corpus callosum and fornix, above, & the two thalami below. It is triangular in shape Its posterior end is broad & lies in the gap b/w the splenium (above) & posterior part of the roof of the third ventricle (below) The anterior end (representing the apex of triangle) lies near the left & right interventricular foramina
    • The median part of the tela choroidea lies on the roof of third ventricle Its right & left lateral edges project into the central parts of the corresponding lateral ventricles.
    • CHOROID PLEXUSES  Highly vascular structures that are responsible for formation of CSF Surface of each plexus is lined by a membrane formed by fusion of ventricular ependyma with pia mater of tela choroidea. Deep to this membrane there is plexus of blood vessels . Microscopically, surface of choroid plexus has numerous villous processes.
    • The blood supply of tela chroidea and choroid plexuses of lateral & third ventricle is derived from choroidal branches of internal carotid and basilar arteries. The venous blood drains in to the internal cerebral veins,which unite to form the great cerebral vein.
    • 4 choroid plexuses are seen in relation to the tela choroidea of third and lateral ventricles. Two of these (one right & one left) lie along the corresponding lateral margins; & project into central part of corresponding lateral ventricle. Two other plexuses run parallel to each other, one on either side of midline. These are choroid plexuses of third ventricle. At each posterolateral angle of tela choroidea the choroid plexus of lateral ventricle continues into inferior horn.
    • CEREBRAL AQUEDUCT  The cerebral aqueduct( aqueduct of sylvius), a narrow channel about ¾ of an inch long, connects the third ventricle with forth ventricle.  It is lined with ependyma and is sorrounded by a layer of gray matter called the central grey.  There is no choroid plexus in the cerebral aqueduct.
    • FOURTH VENTRICLE • The fourth ventricle is a tent shaped cavity filled with cerebrospinal fluid. It is situated anterior to the cerebellum and posterior to the pons and medulla oblongta. • It is lined with ependyma and is continuous above with cerebral aqueduct of midbrain & below with central canal of medulla oblongta and spinal cord. • The fourth ventricle posssess lateral boundaries , a roof , and a rhomboid shaped floor.
    • Lateral boundaries  The caudal part of each lateral boundary is formed by the inferior cerebellar peduncle.  The cranial part of each lateral boundary is formed by superior cerebellar peduncle. Roof / Posterior wall  The tent shaped roof projects in to the cerebellum. The superior part of the roof is formed by superior medullary velum and inferior part by inferior medullary velum.
    •  This part of the roof is peirced in the midline by a large aperture(median aperture of foramen of magendie).  Lateral recesses extend laterally around the sides of the medulla and open anteriorly as the lateral openings of the fourth ventricle or foramen of luschka.
    • POSTERIOR VIEW OF CAVITY OF FOURTH VENTRICLE
    • POSTERIOR VIEW OF FLOOR OF FOURTH VENTRICLE
    • Floor / Rhomboid fossa • The diamond shaped floor is formed by the posterior surface of the pons & medulla oblongta. The floor is divided in to symetrical halves by the median sulcus. • On each side of sulcus, there is an elevation , the medial eminence which is bounded laterally by another sulcus, the sulcus limitans. • Lateral to this sulcus limitans, there is a vestibular area & vestibular nuclei lies behind it. • The facial colliculus is a slight swelling at the inferior end of the medial eminence that is produced by the fibres from the motor nucleus of the facial nerve.
    • • Strand of nerve fibres, the stria medullaris , emerge from the median sulcus & pass laterally over the median eminence and the vestibular area & enter the inferior cerebellar peduncle to reach the cerebellum. • Inferior to the stria medullaris, the most medial structure is the hypoglossal triangle & hypoglossal nucleus lies underneath it. • Lateral to this is vagal triangle , beneath which motor nucleus of vagus nerve lies.
    • Choroid Plexus of Fourth Ventricle  The choroid plexus has a T shape; the vertical part of the T is double. It is suspended from the inferior half of the roof of the ventricle & is formed from the highly vascular tela choridea.  The blood supply to the plexus is from the posterior inferior cerebellar arteries.
    • Central canal of the spinal cord & Medulla oblongta  The central canal opens superiorly in to the fourth ventricle, inferiorly it extends to the medulla oblongta & spinal cord.  In the conus medullaris of spinal cord , it expands to form terminal ventricle .  The central canal is sorrounded by gray matter & there is no choroid plexus in the central canal.
    • CEREBROSPINAL FLUID CSF is found in the ventricles of the brain and in the subarachnoid space around the brain & spinal cord It is a clear, colourless fluid It possesses, in solution, inorganic salts similar to those in the blood plasma The glucose content is about half of blood, & there is only a trace of protein The pressure of CSF may be raised by straining, coughing, or compressing the internal jugular veins in the neck.
    • Physical characteristics & composition of the CSF Appearance Clear and colourless Volume 150 ml Rate of production 0.5ml/min Pressure(spinal tap with patient in lateral recumbant position) 60-150mm of water Composition Protein Glucose Chloride 15-45mg/100ml 50-85mg/100ml 720-750mg/100ml No. of cells 0-3 lymphocytes/cu mm
    • FUNCTIONS OF THE CSF  Cushions & protects the CNS from trauma  Provides mechanical buoyancy & support for the brain  Serves as a reservoir & assists in the regulation of the contents of the skull  Nourishes the CNS  Removes metabolites from the CNS  Serves as a pathway for the pineal secretions to reach the pitiutary gland
    •  The CSF also acts as a “water jacket” for the brain and spinal cord  The 1300 g adult brain weighs approximately 45 g when suspended in CSF
    • CLINICAL NOTES OF VENTRICLES THIRD VENTRICLE  The third ventricle is a narrow space wnich is easily obstructed by local brain tumours or by developmental defects. The obstruction leads to raised ICP in adults & hydrocephalus in children  Tumours in the lower part of the third ventricle give rise to hypothalamic symptoms, like diabetes insipidus, obesity etc.  The site of obstruction can be found out by CT/MRI scans
    • In these scans the third ventricle is seen, normally as a narrow, vertical midline shadow. Dilatation of third ventricle would indicate obstruction at a lower level, e.g. the cerebral aqueduct. If the obstruction is in the third ventricle, both the lateral ventricles are dilated symmetrically. Obstruction at the interventricular foramen causes unilateral dilatation of the lateral ventricle of that side.
    • FOURTH VENTRICLE  Vital centres are situated in the vicinity of vagal triangle. An injury to this area is therefore, fatal  Infratentorial brain tumours & also medulloblastomas block the median & lateral foramina situated in the roof of the ventricle. This results in marked & early rise of ICP
    •  In arnold chiari deformity the medulla & the tonsils of the cerebellum come to lie in the vertebral canal.  Apertures in the roof of fourth ventricle are blocked leading to obstruction to flow of CSF & internal hydrocephalus  Cranial nerves arising from the medulla are stretched  this is a congenital deformity  it is often associated with syringomyelia
    • HYDROCEPHALUS It is an abnormal increase in the volume of the CSF within the skull. It occurs due to various reasons: 1. An abnormal increase in the formation of the fluid 2. A blockage of circulation of the fluid 3. A diminished absorption of fluid
    • Hydrocephalus Communicating vs. Non-communicating • This is an old classification of hydrocephalus • The terms refer to the presence or absence of a communication of the lateral ventricles with the spinal subarachnoid space
    • Non-communicating hydrocephalus • There is obstruction of CSF flow only within the ventricular system.There is no communication between the ventricular system and the subarachnoid space. The commonest cause of this category is aqueduct blockage or stenosis.
    • Communicating hydrocephalus • There is obstruction of CSF flow outwith the ventricular system. In communicating or non-obstructive hydrocephalus there is communication between the ventricular system and the subarachnoid space. The commonest cause of this group is postinfectious and post-hemorrhagic hydrocephalus.
    • Dandy Walker Syndrome • A common cause of obstructive hydrocephalus is Dandy Walker Syndrome where there is blockage of foramina of the 4th ventricle. This is a congenital condition associated with agenesis of the cerebellar vermis.
    • Blockage of CSF resorption • Poor resorption of CSF into the venous sinuses caused by scarring of the arachnoid villi and is commonly seen after meningitis or hemorrhage.
    • Hydrocephalus Ex Vacuo • Hydrocephalus ex-vacuo involves the presence of too much CSF, although the CSF pressure itself is normal. • This condition occurs when there is damage to the brain caused by stroke or other form of injury or chronic neurodegeneration, and there may be an actual shrinkage of brain substance.
    • Normal pressure hydrocephalus • Normal pressure hydrocephalus (NPH) is usually due to a gradual blockage of the CSF drainage pathways in the brain. • NPH is an unusual cause of dementia, which can occur as a complication of brain infection or bleeding (hemorrhage).
    • Treatment of hydrocephalus Ventriculoperitoneal/ventriculoatrial shunting • The two most commonly used shunt systems are the ventriculoatrial (VA) and ventriculoperitoneal (VP) shunts. • The VP shunt is most commonly used as it is simpler to place, extra tubing may be placed in the peritoneum and the consequences of infection are less.