Meninges, Ventricles, & CSF

How does CSF move from the subarachnoid space into the sinuses?

*CSF passes through arachnoid villi (also called arachnoid granulations) into the venous sinus. *These villi protrude through the dura mater and act as one-way valves *CSF flows from the villus and into the venous blood by diffusion as the pressure driving the CSF is higher than that in the venous circulation

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. *Type II (Arnold-Chiari): cerebellar vermal displacement along with hydrocephalus and possible spina bifida

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) and posterior choroidal arterial branches (from posterior cerebral artery).

Epidural hematoma

*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 *If there is on-going bleeding (hemorrhage) from injury, there can be loss of consciousness, followed by lucidity and then deterioration and death.

Subdural hematoma

*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). *May see midline shifts of brain structures.

lateral ventricles

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

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

Dura mater restrict the brain from displacement by several dural septa:

1) Falx cerebri separates cerebral hemispheres 2) Falx cerebelli separates cerebellar hemispheres 3) Tentorium cerebelli separates cerebrum from the cerebellum

Supratentorial herniation

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)

Cerebrospinal Fluid 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.

infratentorial herniation

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

CSF circulation

1. CSF is produced by choroid plexus in each lateral ventricle 2. CSF flows through interventricular foramina into third ventricle 3. choroid plexus in 3rd ventricle adds more CSF 4. CSF flows down cerebral aqueduct to fourth ventricle 5. choroid plexus in fourth ventricle adds more CSF 6. CSF flows out two lateral apertures and one median aperture 7. CSF fills subarachnoid space and bathes external surfaces of brain and spinal cord 8. At arachnoid villi, CSF is reabsorbed into venous blood of dural venous sinuses

There are a total of ___ dural sinuses; ___ major sinus, ___ minor sinus, and ___ unique sinus

11 total dural sinsus 4 major 4 minor 3 unique

The 3 unique dural sinus are:

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

Normal pressure hydrocephalus

A type of communicating hydrocephalus, that is characterized by enlarged ventricles. Characteristic triad of symptoms are dementia, gait problems and urinary incontinence.

Lumbar Puncture / Spinal Tap layers

Adult: L3/L4 or L4/L5 Child: L4/L5 skin subcutaneous tissue supraspinous ligament interspinous ligament ligamentum flavum epidural space (contains the internal vertebral venous plexus) dura arachnoid subarachnoid space: where CSF is drawn from the lumbar cistern.

The blood-CSF barrier is formed by

Blood-CSF barrier separates the arterial blood from the cerebrospinal fluid 1-Choroidal epithelial cells interconnected by tight junctions. The side facing the CSF has an increased surface area due to microvilli. 2-Basement membrane 3-Endothelium - created by pia mater capillaries that contain fenestrations

communicating (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 (obstructive) hydrocephalus

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

epidural hematoma vs subdural hematoma

Epidural hematoma: rapidly expanding with arterial blood usually caused from a skull fracture dura is pushed away from skull by the hematoma Subdural hematoma: slowly expanding with venous blood usually from a torn bridging vein dura is attached to the skull

The 4 major and 4 minor dural sinus are:

Four Major Sinuses: 1-Superior Sagittal Sinus 2-Straight Sinus 3-Transverse Sinus 4-Sigmoid Sinus Four Minor Sinuses: 5-Inferior Sagittal Sinus 6-Occipital Sinus 7-Inferior Petrosal Sinus (left and right) 8-Superior Petrosal Sinus (left and right)

Median aperture (Foramen of Magendie)

From fourth ventricle to Cerebellomedullary cistern (cisterna magna)

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

From fourth ventricle to Quadrigeminal cistern (superior cistern / cistern of the great cerebral vein)

Interventricular foramina - left & right - also called Foramen of Monro)

From lateral ventricle to third ventricle

Cerebral aqueduct (Aqueduct of Sylvius)

From third ventricle to fourth ventricle

There are ____ subarachnoid cisterns and they are:

Interpeduncular cistern pontine cistern quadrigeminal cistern cerebellomedullary cistern

Subarachnoid

Normally present, CSF-filled space; enlarged in cisterns

Tentorial Notch

Opening in the tentorium cerebelli that surrounds the midbrain where the brainstem can enter

Epidural space

Potential space between dura and skull

subdural space

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

damage/injury to a cerebral artery or vein could cause __________

Subarachnoid hemorrhage Intraparenchymal hemorrhage Intraventricular hemorrhage

Endoscopic third ventriculostomy (ETV)

Usually used for obstructive hydrocephalus where a fiberoptic endoscope is maneuvered into the lateral ventricle, interventricular foramen and the 3rd ventricle. There, the floor of the 3rd ventricle can be "broken" to allow CSF release and absorption.

Arachnoid Villi

allow passage of CSF from subarachnoid space into dural venous sinus. Large arachnoid villi are called arachnoid granulations

_______ is thin, delicate and avascular and semi-transparent.

arachnoid mater

Glymphatic system: Drainage formed by _________ that form a perivascular space around arteries and veins within the brain.

astrocytes *This drainage system is most active during sleep! *Removes debris (proteins) discarded by cells through metabolism. *Proteins, like amyloid plaques, can disrupt normal brain function.

the choroid plexus is located in the all the ventricles but

cerebral aqueduct

*Projections of pia mater into the brain ventricles are called __________

choroid plexus

________ is tough and inflexible, sensitive to pain, has it's own blood supply

dura mater

The three layers of the cranial meninges:

dura mater arachnoid mater pia mater

Meningeal artery damage/injury could cause _______

epidural hematoma

Arachnoid Trabeculae

extend to Pia Mater, help to keep brain suspended

Subarachnoid Space

filled with CSF

Dura mater is the _______ of the meninges and had several layers ______

is the thick, tough, outermost membrane of the meninges endosteal layer dural sinus meningeal layer

arachnoid mater is the _________ of the meninges and have several layers ______

middle layer of the meninges arachnoid membrane subarachnoid space arachnoid trabeculae

subarachnoid cisterns

openings in the subarachnoid space created by separation of arachnoid and pia mater, filled with CSF

_________ is thin, delicate and richly vascularized

pia mater

interthalamic adhesion

projection of gray matter from thalamus that connects the right and left side in the third ventricle

Dura mater in the skull vs dura mater in the spine

skull: double layered attached to the inner skull surface spinal cord: single layer, suspended in the vertebral canal

epidural space in the skull vs epidural space in the spine

skull: potential space between dura and skull spinal cord: real space between dura and vertebral periosteum

damage/injury to a vein at attachment to sinus could cause _______

subdural hematoma

Dural venous sinus damage/injury could cause _________

subdural or epidural hematoma

pia mater is the _____________ of the meninges and is bound to the surface of the brain by ________

thin, delicate inner membrane of the meninges astrocytes