Meninges, Ventricles & CSF

Chiari Malformation

*Cerebellar tissues (tonsils) are forced downwards into the foramen magnum / spinal canal because of abnormal development or lack of space in cranial vault. *Several types that increase in severity and may affect the brainstem.

Dandy-Walker Syndrome

*DWS: Dilated 4th ventricle, Water on the brain, Small vermis *Congenital absence of the lateral (Luschka) and medial (Magendie) apertures which can cause hydrocephalus.

Hydrocephalus: What can be done?

*Endoscopic third ventriculostomy (ETV) *Shunt

Dural Venous Sinuses

*Found between layers of dura mater *Receive blood from veins of the brain *Receive CSF from the subarachnoid space *Ultimately drain into the internal jugular vein

Lateral Ventricle

*Left and Right *C-shaped structure in each cerebral hemisphere -(5) parts: -Anterior horn -Body -Posterior horn -Inferior horn -Atrium

Cerebrospinal Fluid (CSF)

*Made by the Choroid Plexus! *Normally, CSF is clear, colorless and odorless *Total volume: ~150ml (adult). ~400-500ml produced and reabsorbed daily

Third Ventricle

*Midline cavity in the diencephalon *"Doughnut" shape *"Doughnut hole" represents the interthalamic adhesion

Fourth Ventricle

*Shaped like a tent with a double peaked roof *The most caudal of the four ventricles with the cerebellum located more dorsally and the pons and medulla more ventrally

Arachnoid Mater

*Thin, delicate and avascular *Attached to the dura mater *Semi-transparent 1) Subarachnoid Space - filled with CSF -Subarachnoid cisterns: openings in the subarachnoid space created by separation of arachnoid and pia mater, filled with CSF 2) Arachnoid Trabeculae - extend to Pia Mater, help to keep brain suspended 3) ArachnoidVilli- allow passage of CSF from subarachnoid space into dural venous sinus. Large arachnoid villi are called arachnoid granulations

Pia Mater

*Thin, delicate and richly vascularized! *Closely adheres to all external surfaces of the CNS. *Projections of pia mater into the brain ventricles are called choroid plexus

Choroid Plexus

-Develops from ependymal cells that line the ventricles *Choroid plexus can be present in the lateral, 3rd or 4th ventricles. *Blood supply from: -Anterior choroidal artery (from internal carotid artery) -Posterior choroidal arterial branches (from posterior cerebral artery). *Choroid plexus is not usually found in the cerebral aqueduct.

Dura matter: 2 layers

-Periosteal -Meningeal

Subarachnoid Cisterns

1- Interpeduncular or chismatic cistern 2- Quadrigeminal cistern 3- Pontine cistern 4- Cerebellomedullary cistern

Brain Herniations Following Injury Supratentorial (structures above tentorial notch):

1-Central (transtentorial) 2-Uncal (transtentorial) - can result in coma/death 3-Cingulate (subfalcine) 4-Transcalvarial

CSF system has two (2) parts:

1-Internal: -includes the lateral ventricles, interventricular foramina, 3rd ventricle, cerebral aqueduct, 4th ventricle (20% total volume) 2-External: -includes the subarachnoid spaces and cisterns (80% total volume) *These two parts communicate via apertures of the 4th ventricle

CSF Function:

1-Mechanical support: -The brain is fully encased in CSF, which reduces the weight of the brain (1500g) to ~25g. Protects again damage from brain's own weight and reduces "traction" on nerves and vessels. 2-Protection: from pressure changes - shock absorber! - provides a cushion to protect from trauma - and immune cells protect against pathogens. 3-Metabolic: Controls brain excitability by regulating ionic composition and supply nutrients and removes metabolites.

Four Major Sinuses:

1-Superior Sagittal Sinus 2-Straight Sinus 3-Transverse Sinus 4-Sigmoid Sinus

Brain Herniations Following Injury Infratentorial (structures below tentorial notch):

1-Upward cerebellar (transtentorial) 2-Downward cerebellar - tonsillar (transtentorial) - rapidly fatal

CSF circulation

1. CSF is produced by choroid plexus in each ventricle 2. CSF flows from lateral ventricles and 3rd ventricle through the cerebral aqueduct into the 4th ventricle. 3. CSF in 4th flows into subarachnoid space by passing through openings in the roof of the 4th ventricle. These openings are the paired lateral apertures and the single median aperture. CSF also fills the central canal of the spinal cord. 4. As it travels through the subarachnoid space, CSF removes waste products and provides buoyancy for the brain and spinal cord. 5.CSF accumulates w/i the suarachnoid space, it exerts pressure w/i the arachnoid villi. This pressure exceeds the pressure in the venous sinuses. Thus, the arachnoid villi extending into the dural venous sinuses provide a conduit for a one-way flow of excess CSF to be returned into the blood within the dural venous sinuses. ---->internal jugular vein

Cerebral aqueduct (Aqueduct of Sylvius)

3rd ---> 4th

Lateral aperture - left & right - (Foramen of Luschka)

4th----> Quadrigeminal cistern (superior cistern / cistern of the great cerebral vein)

Median aperture (Foramenof Magendie)

4th----> cisterna magna (Cerebello-medullary cistern )

Four Minor Sinuses:

5-Inferior Sagittal Sinus 6-Occipital Sinus 7-Inferior Petrosal Sinus (left and right) 8-Superior Petrosal Sinus (left and right)

Other Sinuses:

9-Cavernous Sinus 10-Sphenoparietal Sinus 11-Confluence of Sinuses

Communicating OR Non-obstructive Hydrocephalus

CSF Absorption is impaired. Usually because of functional problems of the arachnoid granulations (villi) or blockage distal to the Foramen of Magendie.

Noncommunicating OR Obstructive Hydrocephalus

CSF Flow is impaired within the ventricles proximal to Foramen of Magendie.

Type II (Arnold-Chiari)

Cerebellar vermal displacement along with hydrocephalus and possible spina bifida

Subarachnoid hemorrhage Intraparenchymal hemorrhage Intraventricular hemorrhage

Cerebral artery or vein----spontaneous aneurysms

Spinal Meninges

Dura mater- 1 layer -Single layer, suspended in vertebral canal Epidural space -Real space between dura and vertebral periosteum Arachnoid -Attached to inner surface of dura Pia mater -Attached to CNS surface, expanded as denticulate ligaments

Subdural or epidural hematoma

Dural venous sinus

Interventricular foramina (Foramen of Monro)

Lateral ---> 3rd

Epidural hematoma

Meningeal artery *Convex / lens shape *Expansion stops at skull sutures (where the dura mater is tightly attached to the skull) *Expansion inward toward the brain rather than along the inside of the skull

subarachnoid space

Normally present, CSF-filled space; enlarged in cisterns

Tentorial Notch

Opening in the tentorium cerebelli that surrounds the midbrain

Cranial Meninges layers

PAD (deep to superficial) -Dura -Arachnoid -Pia

Epidural space

Potential space between dura and skull

Subdural space

Potential space in innermost dural layer, near dura-arachnoid interface

Choroid Plexus & Blood-CSF Barrier

Tight junctions (represented here as dark bars) between choroid epithelial cells prevent substances escaping from blood into CSF = Blood CSF barrier!

Dura Mater: Dural Septa

Tough and inflexible, sensitive to pain, has it's own blood supply *Separates compartments of the cranial vault *Restrict brain from displacement 1) Falxcerebri separates cerebral hemispheres 2) Falxcerebelli separates cerebellar hemispheres 3) Tentorium cerebelli separates cerebrum from thecerebellum

Subdural hematoma

Vein at attachment to sinus *Crescent-shaped with a concave surface away from the skull. *Expansion along the inside of the skull creates the concave shape that follows the curve of the brain. *Expansion stops only at dural reflections(e.g. tentorium cerebelli and falx cerebri).

Lumbar Puncture / Spinal Tap

skin --> subcutaneous tissue--> supraspinous ligament--> interspinous ligament--> ligamentum flavum --> epidural space (contains the internal vertebral venous plexus) --> dura --> arachnoid --> and finally the subarachnoid space, where CSF is drawn from the lumbar cistern.