Increased Intracranial Pressure | Blood-Brain Barrier | Meningeal Irritation Flashcards
Cerebrospinal Fluid (CSF) description
Clear, colorless liquid
Acellular
T or F
No substances normally found in blood that are not also found in the CSF
FALSE
No substances normally found in CSF that are not also found in blood
Walang substances sa CSF na Wala si blood pero may mga substances si blood na wala si CSF
CSF vs Plasma
• Higher concentrations of sodium, chloride and magnesium
• Lower concentrations of potassium, calcium, glucose and protein
Location of CSF
ventricles of the brain and subarachnoid space of the brain and spinal cord
Functions of the CSF
• Cushions and protects the CNS from trauma
• Provides mechanical buoyancy and support
• Reservoir and assists in the regulation of the contents of the skull
• Nourishes CNS
• Removes metabolites (CO2, lactate and hydrogen ions)
• Pathway for pineal gland secretions to reach pituitary gland
CSF appearance
Clear, Colorless
Volume of CSF
c. 150 mL
CSF Rate of Production
0.35 mL/min
Pressure (spinal tap in lateral recumbent position)
60-150 mm H2O
Main sites of CSF Formation
70% choroid plexus (lateral, 3rd, and 4th ventricles)
12% - metabolic water production based on glucose oxidation
18% - capillary ultrafiltrate
CSF is formed under
Hydrostatic pressure
— constantly being formed and removed
Ave intracranial volume
1700 mL
Ave intracranial volume - Brain
1,200 - 1,400mL
Ave intracranial volume -CSF
70-160mL
Ave intracranial pressure - ventricle
25 mL
Ave intracranial pressure - blood
150 mL
CSF average range for formation
21-22 mL/h
(0.35mL/min; 500mL/day)
Bulk volume of CSF is renewed
4-5x/day
Structure of the choroid plexus
• Villous structure extending from ventricular surface into the CSF
• Single layer of cuboidal epithelium with basal infoldings resting on the basement membrane enclosing an extensive capillary network embedded in connective tissue
• Apical microvilli - in contact with CSF
• Tight junctions surround the apical regions of the epithelial cells form a barrier to the passive exchange of proteins and hydrophilic solutes between blood and
CSF
• Regulates production and composition of
CSF
CSF Circulation
Lateral ventricle -foramina of Monroe -
> 3rd ventricles -> cerebral aqueduct -›
4th ventricle -> foramen of Luschka and Magendie -> cerebellomedullary cistern
-> SAS of the brain and SC
CSF Pressure
Highest in the ventricles and diminishes successively along the way
help dive the fluid centrifugally from the ventricles
Arterial pulsations of choroid plexus
CSF Absorption
Passively returned to the venous system via
Arachnoid villi
Structure of Arachnoid villi
Microscopic outgrowth of arachnoid membrane that penetrate the dura and protrude into venous structures
One way valves
Arachnoid villi is most numerous in
Superior sagittal sinus
CSF Absorption
CSF Pressure _ venous pressure
>
Small amount of CSF taken up by
ependyma, arachnoid capillaries, lymphatics and perivascular tissues
• The functioning and survival of all neurons is dependent on the maintenance of physical and chemical milieu within a narrow range.
• Regulate transport of chemical substances
• Barrier system that maintains physiochemical composition of the microenvironment within
Brain barriers
2 types of brain barriers
• Blood brain barrier (BBB)
• Blood-CSF barrier
Structure of blood brain barrier
• Selective semi-permeable membrane between blood and interstitium of the brain, allowing cerebral vessels to regulate molecule and ion movement between the blood and brain
• Separates CSF and brain from blood
Functions of blood brain barrier
• Shield the brain from toxic substances
• Supply brain with nutrients
• Maintain homeostatic environment within the
CNS structures
a continuous homogenous basement membrane and numerous astrocytic processes separates the plasma from the extracellular space within the CNS
Capillary endothelium
Structure of capillary endothelium
a continuous homogenous basement membrane and numerous astrocytic processes separates the plasma from the extracellular space within the CNS
• Capillary endothelium contain tight junctions which restrict intercellular diffusion of solutes
• Selective semi-permeable membrane between blood and interstitium of the brain, allowing cerebral vessels to regulate molecule and ion movement between the blood and brain
• Separates CSF and brain from blood
Blood Brain Barrier
Movement of molecules - water
Diffusion
Movement of molecules
D- glucose, large amino acid
Carrier mediated transport
Movement of extracellular potassium from brain and CSF to plasma against a concentration gradient
Active transport
What molecules do not permeate
Lipid soluble molecules bound to protein
Metabolically active-contains enzymes
Endothelial cells
-Dopa decarboxylase (dopamine to L Dopa; 5-hydroxytryptophan to serotonin)
circumventricular organs (CVOs) - lack endothelial cells barrier but have fenestrated capillary endothelium
circumventricular organs (CVOs)
Have fenestrated capillary endothelium
Have fenestrated capillary endothelium
circumventricular organs (CVOs)
Factors affecting permeability:
Inversely related to the size of the molecules
• Directly related to lipid solubility
Lipid solubility
- gasses and water are readily permeable
- glucose and electrocuted pass more slowly
- almost impermeable to plasma proteins and other large organic molecules
- Compounds w/ MW -> 60000 remain within the circulatory system
Specialized tissued located at strategic positions in the midline ventricular system that are devoid of BBB
Circumventricular Organs
All except — are unpaired and bear relationship with the diencephalon and 3rd ventricle
area postrema
Circumventricular Organs
Pineal body
Subcommissural organ
Subfornical organ
Organism vasculosum of lamina terminals (or supraoptic crest)
Median eminence of hypothalamus
Neurohypophysis
Area posterema
Secretes melatonin hormone into blood
Pineal body
Circulating angiotensin II acts here to inc water intake
Subfornical organ
Osmoreceptor
controlling vasopressin secretion and
thirst
Organum vasculosum of the lamina terminalis
Secretes hormones
Into blood
Post Pituitary
a chemoreceptor trigger zone that initiates vomiting in response to chemical changes in the plasma
Area postrema
Intracranial pressure in lumbar cistern at recumbent position
100-180 mmH2O
3 volumes of intracranial pressure
- Brain parenchyma
- CSF
- Blood volume
Sum of volumes of brain, CSF and intracranial blood is constant.
Monroe Kelly Doctrine
Monroe kelly doctrine
Once the sutures and fontanelles of the skull have closed, the intracranial contents are contained within an unyielding and rigid skull.
The intact cranium and vertebral canal, together with the relatively inelastic dura, form a rigid container such that an increase in the volume of any of its contents-brain, blood, or CSF-will elevate the ICP.
Furthermore, an increase in any one of these components must be at the expense of the other two.
Signs and symptoms of increased intracranial pressure - Compensated stage
Headache
Vomiting
Papilledema
Small increments in brain volume does not immediately raise ICP because of
buffering effect of displacement of CSF from the cranial cavity into the spinal canal
compensatory mechanism for an increased intracranial pressure
there is deformation of the brain and stretching of the infoldings of the falx and tentorium
Inc in intracranial pressure
Once these compensatory measures are exhausted,
a mass within one dural compartment leads to displacement or herniation of brain tissue.
Decompensated stage
Inc in intracranial pressue
• Reduced volume of intracranial blood in veins and sinuses
• Slower formation of CSF
Decompensated stage signs and symptoms
Deterioration of LOC (Level of consciousness)
Crushing’s Triad
• Hypertension
- Bradycardia
• Irregular respiration
Causes on increased ICP
Cerebral or extracerebral mass
Generalized brain swelling
Increase venous pressure
Obstruction to flow and absorption of CSF
CS volume expansion or increase CSF production
Cerebral or extracerebral mass
brain tumor, abscess, hematomas, cerebral infarction with edema
Generalized brain swelling
Hypoxic ischemic encephalopathy
, Hypertensive encephalopathy
Increase venous pressure
cerebral venous thrombosis,
obstruction in jugular veins
CS volume expansion or increase CSF production
- SAH, choroid plexus tumor
abnormal mass of tissue resulting from excessive, uncontrolled cell division; benign or malignant
Tumors
localized collection of pus
Abscess
sac-like pocket of membranous tissue which contains fluid, hair or other substances
Cyst
Localized collection of blood
Hematoma
chronic inflammatory lesion characterized by large number of various cells types (macrophages, lymphocytes, fibroblasts, giant cells), some degrading and some repairing tissues
Granulomas
“water brain”
• Condition of ventricular enlargement due to obstruction to normal CSF
flow
• There is Cor accumuiation under increasing pressure thereby enlarging the ventricles and expanding the hemispheres (children)
Hydrocephalus
Causes of communicating or non obstructive
Overproduction of CSF
Inadequate absorption
Causes of noncommunicating or obstructive
Obstruction of CSF flow
Pathogenesis of Hydrocephalus
Accumulation of CSF and expansion of the ventricles are midirectional
Proximal to the obstruction enlarges
• Ventricle closest to the obstruction enlarges the most
SAH, cerebral hemorrhage or brain abscess that rupture into the ventricles expand the CSF volume by obstruction of CSF pathways within the ventricular system or at basal cisterns
Swelling of the brain due to abnormal shifts of water across various compartments
• The relative volume of brain tissue increases as it swells with edema
Cerebral Edema
Categories of cerebral edema
- Vasogenic
- Cytotoxic
- Osmotic
- Interstitial
Most common
• Disruption of BBB
• lons and proteins flow freely into the extravascular space which draws fluid into the brain interstitium
• Extracellular edema which mainly affects white matter via leakage from capillaries
Vasogenic edema
Causes of Vasogenic edema
Peritumor edema
• Cerebral abscess
• Cerebral hemorrhage
• Extracellular edema which mainly affects — via leakage from capillaries
White matter
Result of inability to maintain Na K ATPase pumps which is responsible for high extracellular and low intracellular sodium concentration
• Sodium accumulates within the cell, drawing water
• Cellular swelling; decreased ECF volume
• Neurons, glia, endothelial cells
• No endothelial dysfunction and does not affect capillary permeability
• Affects gray and white matter
Cytotoxic Edema
Causes of Cytotoxic Edema
• Traumatic brain injury
• Stroke
Results from outflow of CSF from intraventricular space to the interstitial areas of brain
• Increased pressure within ventricles
• Fluid accumulates in the extracellular space of the white matter
• Disruption of ventricular ependymal lining
• Periventricular white matter
Interstitial (Hydrocephalic) Edema
Causes of Interstitial (Hydrocephalic) Edema
• Hydrocephalus
• Meningitis
Results from derangements of osmolarity
• Brain cells pull water from the plasma
• Widespread edema
Osmotic Edema
Causes of Osmotic Edema
Hyponatremia
• Diabetic ketoacidosis
Pressure from a mass within any one dural compartment causes shifts or herniations of brain tissue to an adjacent compartment with lower pressure
Herniation
Most common
• Cingulate gyrus is pushed under the falx
• Generally caused by unilateral frontal, parietal or temporal lobe disease that pushes ipsilateral cingulate gyrus beneath the free edge of the falx cerebri
• Occlusion of ACA resulting to a frontal lobe infarct
• Subfalcial herniation (Cingulate/Subfalcine)
• Or pressure cone
• Downward displacement of the inferomedial parts of the cerebellar hemisphere (tonsils) through the foramen magnum, dorsolateral to cervical cord
• Preterminal event as brainstem is compressed against the clivus
• Medullary compression leads to respiratory arrest
• Neuroimaging: inferior descent of cerebellar tonsils >3mm below the foramen magnum level
(McRae line)
Cerebellar-foramen magnum herniation
(Tonsillar)
• Superior surface of the cerebellar vermis and midbrain are pushed upward compressing the dorsal mesencephalon, adjacent blood vessels and cerebral aqueduct
• Through incisura of the tentorium
• Due to mass effect in the posterior fossa
• Decerebrate posturing
• Upward cerebellar herniation
Downward transtentorial
• Symmetric or severe mass effect resulting in the downward displacement oof the thalami and midbrain
• Central transtentorial herniation
Transtentorial downward
• When an expanding lesion forces the medial edge of the temporal lobe to herniate medially and downward over the free tentorial edge into the tentorial notch
• Uncal herniation
Ipsilateral fixed, dilated pupil due to CN II! compression with or without problems with ocular mobility
• Loss of consciousness due to distortion of the
ARA
ascending reticuber act
system
• Contralateral hemiparesis due to compression of the cerebral peduncles
• Compression of the PCA causing bilateral visual field infarction
Uncal herniation
Herniation of brain external to the calvaria through a skull defect
• Herniated tissue is at risk of ischemia and venous infarction
Extracranial or Transcalvarial
Herniation
Causes of Extracranial or Transcalvarial
Herniation
Trauma
• Post surgical
