Meninges and Cerebrospinal Fluid

Cauda equina

Bundle of nerve roots of the spinal nerves caudal to the second lumbar vertebrae.

Meningitis

Can be viral, bacterial, and fungal induced and life-threatening if not treated properly. Commonly involves arachnoid/subarachnoid space/pia (leptomeningitis). Bacterial most serious (caused by S. pneumoniae and Neisseria meningitidis). Increase WBC count, CSF pressure, protein level. Tx antibiotic, corticosteroid, anticonvulsant, acetaminophen.

Increase in intracranial pressure

Cause by increase in size or volume of any of constituents. Caused by volume increase due to cerebral edema, intracranial hemorrhage or tumors, obstruction of CSF flow, increase blood volume in brain tissue due to venous obstruction.

Structures w/o BBB

Circumventricular organs, pineal body, subcommissural organ, organum vasculosum lamina terminalis (OVLT), neurohypophysis (post pituitary gland), medial eminence, subfornical organ

The great cerebral vein of Galen

Collects venous blood from the internal cerebral v, joins with the straight sinus (cont of inferior sagittal sinus).

Dementia pulgilistica

Common syndrome affecting professional boxers. Generalized brain damage, global cerebral atrophy, develop thinking/memory loss, develop Alzheimer's disease, blindness.

Conus medullaris

Conical shaped caudal end of the spinal cord at the caudal edge of 1st edge of 2nd vertebra. Has thin film enclosed in pia consisting ependymal cells and astrocytes emerge from conus medullaris.

Inner meningeal layer

Continous with the dura of the spinal cord at the foramen magnum (open at base of occipital lobe through which medulla is continuous with the spinal cord). Smooth and avascular and lined with mesothelium on inner surface

Transverse (lateral) sinus

Continuation of the straight sinus around the lateral aspect of the hemispheres

Sigmoid sinus

Continuation of the transverse (lateral) sinuses anteriorly.

Two lateral ventricles

Correspond to shape of hemisphere in which it is located and consists of four parts (C shaped). Connected to 3rd ventricle via channels called interventricular foramen. Anterior (frontal horn)- in frontal lobe Body- in parietal lobe Posterior (occipital) horn- in occipital horn Inferior horn- more ventrally in the temporal lobe.

Tentorium cerebelli

Covering cerebellum. Extends horizontally b/t occipital lobes and cerebellum and attached dorsally to falx cerebri in midline. Divides brain transversely (top from bottom). Forms roof of cerebellum. Ant portion has opening called tentorial notch through the midbrain runs.

Protection of the brain and spinal cord tissue

Cranial vault (skull), dura, arachnoid, and pia mater, and bony vertebral canal.

Arachnoid mater

Delicate (spider-like) AVASCULAR membrane enveloping the brain and spinal cord (medulla spinalis). Can be peeled off. Follows closely the meningeal layer of the cranial dura and separated from it by a potential space called subdural space. Separated from pia by real space subarachnoid cavity, filled w CSF.

Hydrocephalus

Dilation of ventricles ensure when circulation of CSF blocked or absorption is impeded. Leads to increase in ventricular pressure and thus dilation. Can lead to impairment of structures such as the corticobulbal (motor CN) and corticospinal tracts (from lat ventricle getting big)

CSF circulation in brain

Due to pulsations of arteries in subarachnoid space. Flows from each lateral ventricles through interventricular foramen (hole in septum pellucidum) where mixes w more CSF in 3rd ventricle. Then through cerebral aqueduct into 4th ventricle. Leaves via Foramen of Luschka (2 of them) and Magendie and enter cerebellomedullary cistern (aka cisterna magna)

How pressure moves CSF

Dura sinus pressure higher, blood can't flow into subarachnoid space because arachnoid villi tubules collapse. Groups of arachnoid villi form arachnoid granulation which can calcify with age.

Cloudy or white CSF

Increase in number of WBC which signals an infection (bacterial meningitis or viral encephalitis)

Yellow CSF and clot spontaneously

Increased protein content, somtimes due to tumors.

Pia mater

Innermost meningeal layer. Thin, VASCULAR membrane adheres closely to surface of brain and spinal cord. SOme internal structures (ventricles) also covered by pia mater. Gives brain shiny appearance.

Major types of hemorrhage

Intracerebral, extra-epidural, subdural.

Blood brain barrier

Large molecules can't pass from blood into interstitial fluid due to existence of blood brain barrier. Located in interface b/t capillary wall w tight junctions b/t them. Processes of astrocytes abutting on capillaries, a capillary basement membrane. Prevents entry of blood borne foreign substances into brain tissue. Prevents drug delivery.

Falx cerebri

Largest septum. Located longitudinally fissure between the two hemispheres. Sickle-like form. Attached to sup and inf sagittal sinus.

Circulation of CSF listed

Lat ventricle-> interventricular foramen (of Monro)-> 3rd ventricle-> aqueduct of Sylvius (cerebral aqueduct)->4th ventricle-> Foramen of Luschka (2) and Magendie (1)-> Subarachnoid space->arachnoid villi-> superior sagittal sinus

Interpeduncular cistern

Lies over the interpeduncular fossa.

Pontine cistern

Lies over the pons.

Diaphragma sellae

Located on the ventral aspect of the brain. Contains a small hole to accommodate the infundibulum (pituitary stalk) which connects the hypothalamus and hypophysis (pituitary gland).

Fourth ventricle

Located posterior to pons and upper half of medulla and ventral to the cerebellum. Floor is flat and rhomboid-shape and roof is tent shaped with peak of tent projecting into cerebellum. Cerebellum medullary cistern. Communiates with the subarachnoid space via two lateral apertures (Foramen of Luschka) and one medial aperture (Foramen of Magendie).

Venous sinuses

Lots. Formed by periosteum and meningial layers of cranial dura which allows venous drainage from brain.

Intracerebral hemorrhage

May occur during child birth

Types of hydrocephalus

Non-communicating and communicating

Dandy-Walker malformation

Non-communicating hydrocephalus. Cyst formation near internal base of skull, partial or complete absence of area of brain b/t two cerebellar hemispheres and enlargement of 4th ventricle.

Arnold Chiari malformation

Non-communicating hydrocephalus. Indented bony space at lower rear of skull is smaller than normal and pushed and elongates of brainstem and cerebellum.

Supratentorial space

Occupying lesions can cause this v to be compressed and impede the venous outflow of blood from the brain.

Spinal Arachnoid mater

One of three meninges of spinal cord. Connected to the dura via connective tissue, trabeculae. Rostrally passes through foramen magnum to join the cranial arachnoid and caudally to surround the cauda equina.

Spinal dura mater

One of three meninges of spinal cord. Consists of only meningeal layer. Rostrally, the spinal dura joins the meningeal layer of the cranial dura (continuous) at the margin of the foramen magnum. Caudally ends at S2. Becomes thin extension and anchors the spinal dura sac to the vertebral canal.

Spinal Pia mater

One of three meninges of spinal cord. Thicker compared to the cranial pia mater. VASCULARIZED membrane and projects into the ventral fissure of the spinal cord. Toothed ligaments of pia tissue (dentate ligaments) anchor spinal cord to arachnoid and inner surface of the dura.

Spinal dura

Only 1 layer! Single layered and lacks periosteal layer of the cranial dura.

Cranial dura

Outermost meninges, composted of two layers of fibrous connective tissue fused together. Highly vascularized.

Superior sagittal sinus

Part of falx cerebri. Located within the attached borders of the falx cerebri and deviates to posteriorly as the right transverse (lateral) sinus. Receives br from sup cerebral v and v from meninges, scalp, and nose (route to infections of CNS). CSF returned to general systemic circulation.

Cranial epidural space

Pathological conditions cause a space between cranium and dura mater. Not normally there.

Increase in gamma globulin in CSF

Patients with MS or chronic CNS infection

Choroid plexus

Pia mater also part of, a structure which is involved in production of CSF. Present in each ventricle and produces CSF. Lateral ventricles, choroid plexus in medial wall and extends from tip of inferior horn to the interventricular foramen. In 3rd and 4th, in roof.

Straight sinus

Posterior continuation of the inferior sagittal sinus. Empties into transverse (lateral) sinus (usually the left)

Vertebral arteries

Posterior part of dura supplied by brances of vertebral a and occipital arteries.

Occipital arteries

Posterior part of dura supplied by branches of vertebral a and occipital arteries.

Blood-CSF barrier

Prevents large molecules from passing into CSF from blood. Tight junctions DON'T EXIST b/t neighboring capillary endothelial cells in choroid plexus. The cells are fenestrated and allow passage of large molecules, but presence of epithelial cells w tight junctions prevents large molecules from entering CSF.

Functions of venous sinuses

Provide for the venous drainage of blood from the brain mainly to the internal jugular vein. Provide a route by which CSF is returned to the general systemic circulation.

Function of dural septa

Provide support and protection for the brain. Restricts brain movement.

Active transport of CSF

Required to transport Na+ and Mg2+ ions into CSF and remove K+ and Ca2+ ions. Water flows across endothelium to maintain osmotic pressure.

Structures formed by cranial dura mater

Septa and venous sinuses

Septa sinus

Sheet-like processes that are reflected inward and extend from the meningeal layer of the dura deep into the cranial cavity, forming freely communicating compartments. 4 Locations in the brain.

Meninges of spinal cord

Spinal dura, spinal arachnoid mater, spinal pia mater

CSF Function

Structures float in CSF because specific gravities are same (brain and spinal cord). Reduction of traction exerted on nerves and blood vessels w CNS. Cushioning of CNS dampens effects of trauma Vehicle for removal of metabolites. Provides a stable ionic environment.

Middle meningeal a

Supplies lateral cranial dura mater.

Anterior meningeal arteries

Supply anterior part of dura mater.

Dural venous sinuses

are venous channels found between layers of dura mater in the brain.

Aqueduct of Sylvius

connects 3rd and 4th ventricles.

Communicating Hydrocephalus

over production of CSF and movement into the dural venous sinuses are obstructed usually at level of arachnoid villi. Often seen in newborns where there is more fluid made than reabsorbed. Choroid plexus sometimes destroyed.

CSF formation

70% formed by choroid plexus. 30% secreted by parenchymal cell of brain crosses ependyma and enters ventricles. Involves enzyme carbonic anhydrase and specific transport mechanisms. Large things prevented by tight junctions.

Supra-tentorial and infra-tentorial lesions

Above and below the tentoriun cerebelli respectively.

Spinal epidural space

Actual space which venous plexuses are located and is used clinically for the administration of epidural anesthesia (paravertebral nerve block). Located between meningeal layer of the dura and the periosteum of the vertebra.

Subarachnoid space

Actual space. Network of connective tissue or trabeculae which bridges arachnoid and pia membranes. Has CSF which bathes brain and helps distribute and equalize pressure. All major blood vessels of brain located here. Damage can be fatal.

Low glucose in CSF

Acutal bacterial and chronic fungal infections of CNS

Chiasmatic cistern

Adjacent to the optic chiasm

Herniation

After skull sutures have closed, herniation occurs if there is a space-occupying lesion in cranial vault (tumor, hydrocephalus, hematoma, hemorrhage)

Confluence of sinuses

All sinuses empty here. Dilation of venous channels posteriorly where the sup sagittal, straight, and the two transverse (lateral) sinuses converge.

Leptomeninges

Arachnoid and pia mater

Coccygeal ligament

At S2, a caudal thin extension of spinal dura that surrounds the filum terminale.

Cavernous sinus

At base of brain and close to the internal carotid artery. Receives blood from veins of face, pharynx, nose, and thus providing route for CNS infection.

Extra-epidural hemorrhage

B/t periosteal and meningeal layers of cranial dura

Subdural hemorrhage

Bleeding in the "potential" space between dura and arachnoid membranes. Most commonly from tearing superior cerebral v. Sudden blow to front of head

Pink or red CSF

Blood in CSF usually due to rupture or bleeding from aneurysm of vessels in subarachnoid space

Choroid plexus Membranes

Endothelial layer of choroidal capillary wall (fenestrated, openings) Pia Membrane Choroidal epithelial cells contain numerous mitochondria and many basal in folding and microvilli facing ventricles. Tight junctions found b/t adjacent chroidal epithelial cells.

Inferior sagittal sinus

Extends along inferior margin of falx cerebri. Drains blood predominantly from the medial aspect of the brain.

Lumbar cistern

Extends from L1 to S2 of the vertebral column. Can perform lumbar puncture or spinal tap at L3-L4 in adults and L4-L5 in children. Administer drugs.

Filum terminale internum

Extends from conus medullaris and passes through the caudal end of the dural sac at S2 surrounded by coccygeal ligament.

Non-communicating Hydrocephalus

Fluid flow out of one or more of ventricles is blocked. Most common blockage of cerebral aqueduct of foramina of 4th ventricle. Medulla squashed and can cause death.

Two lateral aperture of 4th ventricle

Foramen of Luschka

One medial aperture of 4th ventricle

Foramen of Magendie

Third ventricle

Forms the medial surface of the thalamus and hypothalamus. Anteriorly, thin plate or wall called the organum vasculosum lamina terminalis (OVLT) forms the anterior end of 3rd ventricle. Connected to 4th ventricle via cerebral aqueduct (aqueduct of Sylvius).

Symptoms of intracranial pressure

Headache, nausea and vomiting, bradychardia (increased pressure on nucleus and dorsal motor nucleus of vagus nerve in medulla), increase in systemic pressure (on ventrolateral medulla), blurring optic disc margin.

Xanthrochromia

Hours after subarachnoid hemorrhage, hemoglobin from lysed RBC broken down into bilirubin (yellow)

Head injury and resultant hemorrhage

Usually fractures to base of skull which increases the risk of CSF from nose, bleeding from auditory canal, meningeal bleeding, infections.

CSF circulation in body

Travels rostrally over cerebral hemispheres enters arachnoid villi. Flow into dural venous sinuses but can't in opposite direction because of pressure in subarachnoid space is higher. From Cisterna magna, flows downward into spinal subarachnoid space and ascends along ventral surface of spinal cord into basal part of brain, courses dorsally to empty into dural sinuses.

Four cavities (ventricles) of brain

Two lateral ventricles, 3rd ventricle, and 4th ventricle.

Interventricular foramen

Two short channels connecting both lateral ventricles to the 3rd ventricle.

Tonsillar herniation

The tonsil (a tiny structure medial to cerebellum) herniates into foramen magnum. Because of medullary position of reticular formation, this herniation is very serious.

Uncal herniation

The uncus (tiny structure of medial temporal lobe) herniates into tentorial notch and puts pressure on midbrain. Decreased consciousness and eventually death. Pupil dilated.

Dentate ligaments

Toothed ligaments of pia tissue that anchor spinal cord to arachnoid and inner surface of the dura.

Types of brain herniation

Uncal, central, cingulate, transcalvarial, upward, tonsillar

Falx cerebelli

Vertically oriented triangular projection into post fossa (portion of brain below the tentorium-infra-tentorial space). Dural fold b/t folds of cerebellum in the post fossa. Analogous to flax cerebri.

No change in glucose CSF but sick patient

Viral infection

Perivascular space

When blood vessels penetrate brain tissue, they carry a cuff of pia and arachnoid into the brain for a short distance creating this space. Continous w subarachnoid space, may serve as passage for CSF movement into brain.

Cerebellomedullary cistern

aka Cisterna Magna. Spans space over the cerebellum and medulla. It is the largest cistern.

Cisterna magna

aka cerebellomedullary cistern

Arachnoid villi

aka granulation. At the sinuses (especially sup sagittal and dural sinuses) minute pieces of arachnoid penetrate through apertures in meningeal layer and protrude into venous sinuses. Main passageway for CSF in general systemic circulation.