Ventricles and Meninges (Glendinning)

Question 1

Identify and describe the location and function of the meningeal layers surrounding the spinal cord and brain.

Answer 1

Dura:
Brain: two layers: periosteal (next to skull) and meningeal
- Superior sagittal sinus is formed with periosteal layer enters longitudinal fissure
Spinal cord: 1 layer - true epidural space

Arachnoid (loose covering like a sock)
Brain: arachnoid trabeculae and many cisterns (enlarged areas of subarachnoid space)
Spinal cord: fewer trabeculae and 1 cistern

Pia
Spinal cord: forms denticulate ligaments, filum terminale (anchors conus medullaris to dura and arachnoid)

Question 2

Explain the flow of CSF beginning from the choroid plexus to the arachnoid villae.

Answer 2

CSF produced by CHOROID PLEXUS within brain ventricles.

1. Lateral ventricles in cerebral hemispheres
2. Interveterbral foramen of Monroe
3. 3rd ventricle in the diencephalon
4. Cerebral aqueduct of sylvius in midbrain (mesencephalon)
5. 4th ventricle in pons/medulla
6. foramen of magendie (1 median aperture) and luschka (2 lateral aperture)
7. subarachnoid space around brain and spinal cord
8. arachnoid granulations (near superior sagittal sinus) = projections of arachnoid villi
9. veinous sinuses in subdural space

Question 3

Describe and give the clinical rationale for the lumbar puncture.

Answer 3

Performed at L3-L4 in adults, L4-L5 in children

1. Obtain samples of CSF
   - subarachnoid hemorrhage (blood)
   - infections, e.g., meningitis (inc protein, inc WBC, dec glucose)
   - GBS (inc protein w/o inc. in cells)
   - MS (lumbar puncture to confirm MS - inc IgG, not diagnosis)
2. Introduce drugs (i.e. chemotherapeutic)

**LP contraindicated if there is inc ICP b/c tectorial or cerebellar herniation could occur

Question 4

Define hydrocephalus and explain potential causes.

Answer 4

“water in the head”

Condition of excess CSF

1. Excess production (choroid plexus tumors)
2. Obstructed flow anywhere in ventricles or subarachnoid space (tumors, malformations, hemorrhage)
3. Decreased reabsorption via arachnoid granulations

Communicating: lateral ventricles communicate w/ subarachnoid space so problem could be w/ choroid plexus - excess

Non-communicating: flow obstructed WITHIN ventricular system

Question 5

Identify the dural folds and be able to describe, generally, the common areas of brain herniation.

Answer 5

Falx cerebri

Falx cerebelli

Tentorium cerebelli: Create SUPRATENTORIAL and INFRATENTORIAL cavities (between posterior cerebral hemispheres and cerebellum)

Diaphragm sellae - circular fold beneath the brain that covers the sella turcica

Common areas:

1. Subfalcine
   - Subdural: cingulate gyrus herniates below falx cerebri (might get a headache but nothing severe)
2. Transtentorial and central
   - tumor in temporal lobe - tumor herniates through tectorial notch (uncal herniation -> COMA!)
3. Tonsillar
   - Cerebellar tumor herniates through foramen magnum -> will impact medulla: cardiorespiratory center -> DEATH!

Question 6

Describe the locations and causes of epidural, subdural, and subarachnoid hematoma.

Describe the major symptoms that characterize each of these types of events.

Answer 6

epidural: b/w dura and skull
- trauma to the skull (MMA)
- may also be from sinuses (~15%)
- “Lens shaped” structure on MRI
- often has period of lucidity (“i’m fine, i’m fine”) before severe symptoms

subdural: b/w arachnoid and dura
- tearing of bridging veins (elderly usually)
- crescent-shaped structure on MRI
- slow bleed, veinous blood, less pressurized

subarachnoid: b/w pia and subarachnoid (where major blood vessels are found)
- bleeding into subarachnoid space usually secondary to head trauma
- usually traumatic
- “non-traumatic” from bleeding from an A-V malformation or ruptured aneurysm (most occur in “anterior circulation” supplied by internal carotid artery - AComm [men], PComm [women])
- sudden-onset, severe headache (from blood irritating meninges - which is full of pain receptors)

Question 7

Circumventricular organs

Answer 7

regions w/ fenestrations - no BBB (mainly around third ventricle)

enables brain to respond to changes in blood chemistry (example: osmolarity)

Sensory CVO: provide direct info from systemic circulation to ANS

• Area postrema - vomiting center so when there are toxins in blood, can elicit vomiting
• Subfornical organ - active in osmoregulation, CV regulation, and E regulation
• Organum vasculosum - responsible for homeostatic conversation of osmolarity

Secretory CVO: secrete hormone + glycoprotein in response to info received from brain environment and external stimuli

• Subcommisural organ - secrete glycoprotein SCO-spondin
• Pineal gland - secrete melatonin
• Posterior pituitary - store and release oxytocin and ADH made by hypothalamus
• Median eminence - allow for transport of neurohormones from CSF to peripheral blood supply

Question 8

Chiari Malformations I-IV

What it is?

Symptoms?

Answer 8

Congenital hindbrain anatomic anomalies associated w/ cerebellum, brainstem, or craniocervical junction.

RESULT: downward displacement of cerebellum (tonsils herniate through foramen magnum)

Symptoms usually in ADULTS, caused by:

1. compression of medulla and upper spinal cord
2. compression of cerebellum
3. disruption of CSF flow through foramen magnum
4. produce hydrocephalus

Chiari I (most common)

• cerebellar tonsils below foramen magnum
• syringomyelia (name of cyst)
• compression of brainstem
• most common symptoms: headache (inc. pressure), ataxia (cerebellar dysfunction), impaired movement (brainstem compression)

Chari II (less common)

• Cause significant herniation through foramen magnum
• Cause acqueductal stenosis and hydrocephalus
• Usually with meningomyocele

Question 9

Hydrocephalus: Classic triad of symptoms – elderly

Answer 9

Gait disturbance: usually the first symptom; magnetic gait (legs stuck to ground)
Dementia (of varying degrees)
Urinary incontinence: may present as urgency, frequency, or diminished awareness of need to urinate

**NOTE: NO HEADACHE (no inc. pressure) ?!

Question 10

Describe characteristics of the choroid plexus.

Answer 10

1. Ventricles lined w/ ependymal cells w/ adhering junctions -> allow free movement of CSF into brain
2. At choroid plexus, ependymal cells form tight junctions (creating choroid epithelium) -> BLOOD-CSF barrier
3. Choroid epithelium has active transport (ion exchange mechanisms) to determine flow of molecules (e.g., Na+, K+, Cl-, Mg2+, floats)
4. Choroidal capillaries = fenestrated w/ no tight junctions (leaky)

Question 11

What makes up the BBB?

Functions?

Answer 11

Capillary endothelium + astrocyte foot processes

• Controls ionic environment - neurotransmission
• Protects brain from toxins
• Prevents drugs from entering brain
• Contains transporters for some critical molecules (glucose + proteins)

BBB may be disrupted by infections, tumors or trauma -> “vasogenic edema”

Question 12

What is a cistern? (4)

Answer 12

Enlarged area of subarachnoid space

Interpenduncular
Prepontine
Cisterna magna
Quadrigeminal