Meninges & CSF and Ventricular system D.Nimer D.Rania Gabr D.Safaa D.Elsherbiny

Objectives Describe the arrangement of the meninges and their relationship to brain and spinal cord. Explain the occurrence of epidural, subdural and subarachnoid spaces. Locate the principal subarachnoid cisterns, and arachnoid granulations. Describe the ventricles of brain and importance of their choroids plexus. Summarize the pathway of cerebrospinal fluid (CSF) circulation Identify brain ventricles in CT scan, MRI .

CSF Def: CSF is clear, colourless, and odourless fluid Site: fills the ventricles of the brain and the subarachnoid space. Volume: about 130 ml mainly in the subarachnoid space: 30 ml in the ventricles 100 ml in the subarachnoid space. Choroid Plexus Formation: combination of : capillaries, pia and ependyma

CSF Formation Formation: formed by active secretion and by diffusion from: Choroid plexus: is the main source of the CSF (70%). It is produced mostly by the choroid plexus of the lateral ventricle. Ependymal lining of the ventricles. Cells of the pia mater.

Circulation

https://www.youtube.com/watch?v=JCf273U0ktc

Circulation It flows from the lateral ventricles to the third ventricle through the interventricular foramina of Monro, then to the fourth ventricle through the aqueduct of Sylvius. More CSF is added in each ventricle. It leaves the fourth ventricle to the subarachnoid space through the median foramen of Magendie and the lateral foramina of Luschka. A small amount flows to the central canal of the spinal cord. The CSF flows in the subarachnoid space around the brain and the spinal cord. The following factors facilitate the CSF circulation: Pulsations of the arteries in the subarachnoid space. Movements of the cilia of the ependymal cells. Positive and negative pressure created by continuous production and absorption.

Functions of CSF Reduces the brain weight 60 folds (from 1400 gm to 25 gm). Protects the brain and the spinal cord. Substitutes the lymphatic system in the CNS and provides a drainage system for the brain by transferring waste products from the CSF to the blood. Maintains the chemical environment for the CNS through communication with the brain extracellular space. Regulation of the intracranial pressure

CSF Drainage The CSF returns to the vascular system by: Main site for drainage: arachnoid villi & granulations. They drain the CSF into the venous blood of the dural sinuses especially the superior sagittal sinus. Gap junctions between ependymal cells & between pial cells back to the brain tissue. Into the venous blood through small veins in the subarachnoid space. Into the perineural lymph vessels around the cranial and spinal nerves.

In certain areas, arachnoid projects into the venous sinuses to form arachnoid villi (arachnoid villi ) through which cerebrospinal fluid diffuses into the bloodstream.

Clinical Conditions Associated with the CSF Hydrocephalus:  Definition: It is an abnormal increase in the volume of the CSF with dilatation of the ventricles and increase in size of the head.   Causes: Obstruction to its circulation: It is the commonest cause. The commonest site of obstruction is the aqueduct of Sylvius. 2. Overproduction of the CSF: by choroid plexus tumor (rare). 3. Inadequate drainage of the CSF: by thrombosis of the superior sagittal sinus.

2. Lumbar puncture: It means introducing a needle into the subarachnoid space for: Injecting drugs into the CSF such as anaesthetics and antibiotics. Obtaining a sample of CSF for analysis. Measuring the CSF pressure by attaching a manometer to the needle.

3. Papilledema: edema of the optic disc usually due to increased intracranial tension

Subarachnoid Space Varies in depth , forming : Subarachnoid Cisterns: 1- The cisterna magna: or cerebllomedullary cistern which lies between the inferior surface of the cerebellum and the back of the medulla. 2-The interpeduncular cistern: This cistern contains the optic chiasma & circle of Willis. 3- Pontine cistern(Prepontine cistern or cisterna pontis). Surrounds the ventral aspect of the pons.Contains VI cranial nerve.

VENTRICULAR SYSTEM Comprises of: two lateral ventricles third ventricle cerebral aqueduct the fourth ventricle

Lateral ventricle Def: It is the cavity of telencephalon Shape: C-shaped cavity Site: within each cerebral hemisphere Parts: Anterior horn: in frontal lobe Body: in parietal lobe Posterior horn: occipital lobe Inferior horn: temporal lobe

Lateral ventricles

Third Ventricle Definition: the third ventricle is the cavity of the diencephalon It is a narrow cavity between the 2 thalami.

Boundaries Posterior wall: Anterior wall: Posterior commissure Pineal gland Habenular trigone Anterior wall: Lamina terminalis Anterior commissure

Roof: Ependymal layer Two internal cerebral veins Tela choroidea Floor: Optic chiasma, tuber cinereum, infundibulum and mamillary bodies Posterior perforated substance

Lateral wall: Thalamus. The 2 thalami are connected in 70% by interthalamic adhesion. Hhypothalamus.

Choroid plexus (of 4th ventricle) Site: projects downward from roof of the 3rd ventricle. Shape: 2 vascular ridges, one on each side of midline. Supplied by the posterior choroidal artery (branch from the posterior cerebral artery). Communication: With the lateral ventricles: through the interventricular foramina of Monro. With the fourth ventricle: through the cerebral aqueduct of Sylvius.

4th ventricle Def: is the cavity of Rhombencephalon Site: Between: cerebellum (posterior) dorsal surface of pons and dorsal part of upper medulla (anterior). 2 angles: Upper angle Lower angle.

Roof (posterior)of the 4th ventricle Boundaries Roof (posterior)of the 4th ventricle Roof : Superior medullary velum: above. Inferior medullary velum: below. Cerebellum: middle. superior medullary velum Cerebellum Inferior medullary velum

Floor (anterior) of the 4th ventricle

Floor: Upper pontine: dorsal surface of pons. Lower medullary: dorsal surface of upper part of medulla. Intermediate: stria medullaries of 4th ventricle. laterally Superior cerebellar peduncle. Middle cerebellar peduncle Inferior cerebellar peduncle

Communication Above: with 3rd ventricle through aqueduct of sylvius. Below: with central canal of spinal cord. With subarachnoid space through: foramens of Lushka and Magendi.

Choroid plexus (of 4th ventricle) T-shaped. Inner surface of inferior medullary velum Supplied by PICA

Normal Brain

Normal Ventricles

Hydrocephalus

Normal ventricles and hydrocephalus

A) Pre-operative axial head CT scan demonstrating enlarged ventricles.

B) Post-operative axial head CT demonstrating decrease in the size of the lateral and third ventricles after shunt placement.