2. Meninges and CSF Flashcards
What does the dura cover?
Brain, spinal cord, cranial nerves, optic chiasm
Where are sinuses located?
Within the dura mater
Where do the sinuses drain venous blood?
Jugular veins –> SVC
What landmark distinguishes the end of the brainstem and the beginning of the spinal cord?
Foramen Magnum
Falx cerebri
Attached to skull, goes down to corpus callosum
Separates brain into two hemispheres
Where is the superior sagittal sinus?
Top of falx cerebri
Tentorium cerebelli vs falx cerebelli
Tentorium cerebelli covers the top of the cerebellum, separates it from the occipital lobe
Falx cerebelli divides the cerebellum into two hemispheres
What is the tentorium notch?
It is the space in the tentorium cerebelli through which the brainstem passes
What happens during uncal herniation?
Increased intracranial pressure (ICP) causes the uncus to herniate and get stuck under the tentorial notch
Epidural space in brain vs spinal cord
In brain, it is a potential space
In SC, it is a real space
Space between skull and dura; space between dura and vertebrae
Is the subdural space a real space or a potential space?
Potential space. Dura and arachnoid are usually fused
In which meningeal space is the CSF?
Subarachnoid space
In what cases do epidural hematomas occur? Describe what happens
Tearing of middle meningeal artery or tearing of venous sinus –> quick bleeding –> accumulation of blood –> rapid rise of pressure (dura can dissect off bone)
Where does the bleeding occur with an epidural hematoma vs subdural hematoma?
Epidural = above dura; subdural = inbetween dura mater and arachnoid
Consequences of epidural hematoma?
Compression and midline shift of brain
Can effect/damage optic chiasm (dilated pupil that doesn’t constrict)
Coma and death can result
Consequences of subdural hematoma?
Dissect arachnoid off dura; blood distributed throughout entire hemisphere
Can also lead to brain compression, similar symptoms as epidural
Slower onset than epidural since it involves brain
Subdural hematoma involves damage to what structure(s)? Significance of this?
Cerebral vein; bleed is lower pressure and occurs more slowly
Why does the risk of tearing increase as we age?
Brain shrinks, pulls away from sinus –> greater risk for tears
Younger people and more susceptible to _________ hematomas, and elderly are more susceptible to ______________ hematomas.
Younger people –> epidural hematomas
Elderly –> subdural hematomas
Composition of CSF
little glucose/protein/cells, chloride
What happens to CSF with meningitis?
CSF may be cloudy with presence of bacteria (also notable difference in composition of CSF)
Functions of CSF (6)
Bouyancy and support
Cushion and protect
Nourishment
Reservoir and regulation of the contents of skull
Removes metabolites
Pathway for pineal secretions to reach pituitary gland
Where is choroid plexus located?
In all of the four ventricles
Describe the flow of CSF
lateral ventricles –> interventricular foramin of Monroe –> 3rd ventricle –> cerebral aqueduct –> 4th ventricle
If it goes through foramin of magendie (median aperture) –> flows up around the brain into subarachnoid space
If it goes through the foramen of luschka (lateral aperture)–> flows in and around SC
Subarachnoid cisterns
Separation of pia and arachnoid further, allowing for CSF to pool in these areas called cisterns.
pia adheres to the surface of the brain, but arachnoid covers only superficial surface. In certain areas around brain, the pia and arachnoid are separated widely; in such regions are formed cavities called the subarachnoid cisterns
Name the three cisterns
Quadrigeminal cistern
Pontine cistern
Cisterna magna
Location of the three cisterns
Quadrigeminal - between superior and inferior colliculi of brain
Pontine - ventral aspect of pons
Cisterna magna - below fourth ventricle at level of medulla (below-ish of cerebellum)
Where does lumbar puncture occur?
Level of iliac crest (L4); damage doesn’t occur because no SC at this segment, only cauda equina
Arachnoid villus. What does it do?
Protrusions of arachnoid into dural sinus
Reabsorb CSF into venous sinus –> one way flow from subarachnoid space into venous blood (can move through large vacuoles or paracellularly)
Difference between arachnoid villus and arachnoid granules
Individual tufts = villus
Groups of arachnoid villi = granules
Brain receives what percent of CO and O2?
Receives 15% of CO, 20% of O2
Does the brain’s metabolic rate vary with state and activity?
Varies ONLY SLIGHTLY with state and activity
What conditions can vary the metabolic rate of the brain?
General anesthetics, hypoglycemic coma, and seizures
Under what MABP does autoregulation NOT occur?
60-150mmHg
Which conditions would cause a vasodilation?
Inc. PCO2
Dec O2
Inc H+
Which conditions would cause a vasoconstriction?
Inc. PO2
Dec PCO2
Equation relating MABP, ICP, and CPP
CPP = MABP - ICP
What is ICP
intracranial pressure = pressure of the fluid in the brain
What is normal ICP (in mmH20 and mmHg)?
Elevated ICP?
65-150mmH20
5-15mmHg
Elevated ICP: >20mmHg
At what ICP does cerebral circulation collapse?
ICP = 90-100mmHg
When ICP > MABP
What are the three main herniations that can occur in the brain?
Cingulate gyrus herniation, uncal herniation, tonsil herniation
In which case does cingulate gyrus herniation occur
Occurs with subdural hematoma
Tonsil hernation
occurs when tonsil of cerebellum herniates through foramen magna leading to compression of medulla
Symptoms of inc ICP
Headache, papilledema, altered mental status, increased BP, decreased HR
What is papilledema
Effusion or edema in and around eye = eye appears cloudy
What is Cushing’s reflex (triad)
Inc systolic BP, inc pulse pressure, dec HR
What are the three types of cerebral edema?
vasogenic edema, cytotoxic edema, and interstitial edema
Describe vasogenic edema
Inc permeability of BBB leads to an increase in ECF
Describe cytotoxic edema
Due to hypoxia or failure of Na/K pump –> inc intracellular fluid and cell swelling
Describe interstitial edema
inc edema and fluid in white matter around ventricles, due to hydrocephalus or increased CSF
How to lower ICP
Hyperventilate with respirator
Elevate head to 30 degrees
Maintain BP in normotensive state
(High BP inc ICP, low BP compromises cerebral blood flow)
