Ventricular system of the brain

lectures

1. Ventricular System of the Brain

2. Ventricular System of the Brain The ventricular system of the brain consists of two lateral ventricles and the midline 3rd and 4th ventricles connected by the cerebral aqueduct. Each lateral ventricle opens through an interventricular foramen into the 3rd ventricle. 2

3. Cerebrospinal fluid (CSF) Cerebrospinal fluid (CSF) – filtrate of the blood that helps protect the brain and may provide nutrients to the structures it bathes. CSF is secreted by the choroid plexus within the ventricles, which are located inside the brain, and it is found in the ventricles, the subarachnoid space, and the cisterns, which are all continuous with one another. The CSF is returned into the superior sagittal venous sinus by arachnoid villi , which are essentially a one-way valve for the CSF to re-enter the bloodstream. 3

4. Circulation of cerebrospinal fluid (CSF) Cerebrospinal fluid is a clear colorless fluid, which acts as a transport medium for nutrients and waste products and provides a protective fluid cushion for the central nervous system. CSF is secreted (at the rate of 400-500 mL daily) by choroidal epithelial cells (modified ependymal cells) of the choroid plexuses in the lateral, 3rd, and 4th ventricles 4

5. Circulation of cerebrospinal fluid (CSF) The vascular source of the choroid plexus differs between the lateral and third ventricles, and the fourth ventricle. The lateral and third ventricles are supplied anteriorly by the  internal carotid  and choroidal branches of the posterior cerebral artery, whereas the fourth ventricle, being much lower in position, is supplied by the inferior cerebellar arteries . Cerebrospinal fluid is constantly produced at a secretion rate of 0.35-0.40 ml/min, and replaced with an average volume of 150 mL in the ventricular system/subarachnoid space. Of this volume, about 125 mL is intracranial and 25 mL of this volume lies within the ventricles 5

6. Circulation of cerebrospinal fluid 6 CSF drains from lateral ventricle interventricular foramina third ventricle cerebral aqueduct of Slyvius fourth ventricle median and two lateral apertures subarachnoid space arachnoid granulations superior sagittal sinus vein CSF drains into the subarachnoid space from the 4th ventricle through a single median aperture and paired lateral apertures . If they are blocked, CSF accumulates and the ventricles distend, producing compression of the substance of the cerebral hemispheres.

7. Luschka Lateral Drains to subarachnoid space Magendie middle CSF flow Lateral ventricle Foramen of Monroe 3 rd ventricle “Aqueduct of Sylvius” 4 th ventricle Central canal Foramen of Luschka & Magendie 7

8. Circulation of cerebrospinal fluid (CSF) Median aperture Lateral aperture 8

9. Cerebrospinal fluid (CSF) Clinical Note : If flow of the CSF is blocked, it will lead to hydrocephalus , which means “water on the brain”. If the hydrocephalus is caused by the overproduction or reduced reabsorption of CSF, it is called a communicating hydrocephalus . A non-communicating hydrocephalus results when the CSF is blocked somewhere within the ventricular system of the brain and can not reach the subarachnoid space. What type of hydrocephalus would result from meningitis ? 9

10. Leakage of Cerebrospinal Fluid Fractures in the floor of the middle cranial fossa may result in CSF leakage from the external acoustic meatus (CSF otorrhea) if the meninges superior to the middle ear are torn and the tympanic membrane is ruptured. Fractures in the floor of the anterior cranial fossa may involve the cribriform plate of the ethmoid, resulting in CSF leakage through the nose (CSF rhinorrhea). 10

11. Leakage of Cerebrospinal Fluid CSF can be distinguished from mucus by testing its glucose level; the glucose level of the CSF reflects that of the blood. CSF otorrhea and rhinorrhea may be the primary indications of a cranial base fracture and increase the risk of meningitis because an infection could spread to the meninges from the ear or nose 11

12. Brain Parts of the Brain: The brain is composed of the Cerebrum, Cerebellum, and Brainstem. When the calvaria and dura are removed, gyri (folds), sulci (grooves), and fissures (clefts) of the cerebral cortex are visible through the delicate arachnoid—pia layer. 12

13. Cerebral Injuries Cerebral concussion is an abrupt, brief loss of consciousness immediately after a head injury. Consciousness may be lost for only 8-10 sec, as occurs in a knockdown during boxing. The injuries result from acceleration and deceleration of the head that shears or stretches axons (diffuse axonal injury). The sudden stopping of the moving head results in the brain hitting the suddenly stationary cranium. 13

14. Cerebral Injuries Cerebral contusion results from brain trauma in which the pia is stripped from the injured surface of the brain and may be torn, allowing blood to enter the subarachnoid space. It may result in an extended loss of consciousness , but if there is no diffuse axonal injury, brain swelling, or secondary hemorrhage, recovery from a contusion may be excellent. Cerebral lacerations are often associated with depressed cranial fractures or gunshot wounds. Lacerations result in rupture of blood vessels and bleeding into the brain and subarachnoid space, causing increased intracranial pressure and cerebral compression. 14

15. Cerebral compression Cerebral compression may be produced by: Intracranial collections of blood. Obstruction of CSF circulation or absorption. Intracranial tumours or abscesses. Brain swelling caused by brain edema, an increase in brain volume resulting from an increase in water and sodium content 15