Module 11 - Herniation Syndrome Flashcards
Normal ICP{
5-15 mmHg`
The head is a confined cavity with a non expandable skull, what are the 3 compatments that make up the volume?
10% - Blood volume
10% CSF
80% Brain tissue
Monroe Kellie Hypothesis
change in volume of one compartment can be compensated for by a change in one or both of the other two compartments
What two compartments are most able to compensate for changes in ICP?
CSF or Blood Volume
What can increase CSF
excessive production
decreased absorption
obstructed circulation
What can decrease CSF
translocation to the spinal subarachnoid space (basal cisterna)
or
Increased reabsorption
What can increase Blood Volume (BV)
vasodilation of cerebral blood vessels
OR
obstruction of venous outflow
What can decrease Blood volume
low pressure venous system has limited buffering capacity (since blood likes to go high to low)
blood flow control by autoregulatory mechanisms (hyperventilation to decrease PCO2 which leads to vasoconstriction (which can lower blood volume)) - but vasoconstriction is temporary before compensation through vasodilation
Effects of Increased ICP
obstructs cerebral blood flow (cannot go high to low or it cant flow at all)
destroys brain cells
displaces brain tissue (herniation)
damages delicate brain structures
Cerebral Compliance
as cerebral volume increases from brain tumor, cerebral edema, and hematoma there is some compliance in pressure to allow change in volume
Change in volume / Change in Pressure!!!
Pressure-Volume Curve
once compensatory mechanisms are exceeded, even small changes in volume cause dramatic increases in pressure in the brain
Cerebral perfusion pressure
70-100 mmHg
CPP = MABP - ICP
Brain ischemia occurs in CPP is…
<50-70 mmHg
If ICP is greater than or equal to MABP, what happens?
there is a very low pressure so inadequate tissue perfusion, cellular hypoxia, and neuronal death occur
Stages of Intracranial HTN
Stage 1 - Compensation
Stage 2 - Increased ICP
Stage 3 - Decompensation
Stage 4 - Herniation or Loss of CPP
Stage 1: Compensation
occurs on a normal basis
increased volume in one compartment –> decrease in one or both of other compartment volumes
ICP remains near normal
Stage 2: Increased ICP
Brain responds by constricting cerebral arteries to reduce pressure but results in hypoxia and hypercarbia and deterioration of brain function
Stage 3: Decompensation
cerebral arteries respond to hypoxia and hypercarbia with reflex dilation –> this increases Blood volume –> this further increases ICP
Small changes in intracranial volume at this point results in large changes in pressure
Stage 4: Herniation or Loss of CPP
Swelling and pressure lead to herniation
if ICP = MABP (or higher than) means there is no cerebral perfusion
The earliest and most reliable sign of increased ICP is…
decrease in level of consciousness
Cushing Reflex
CNS ischemic response triggered by ischemia of vasomotor center in the brain
Rarer nowadays because of ICP monitoring
Late indicator of Increased ICP
A last ditch effort
What are the three responses in the Cushing Triad/Reflex
- Increased MABP (body trying to perfuse brain)
- Widening Pulse Pressure (systolic - diastolic because diastolic gets very high)
- Reflex Bradycardia (baroreceptors in carotids tell vasomotor center to tell vagus center to slow heart to decrease ICP and prevent herniation)
What does it mean by the Cushing Reflex being a Last Ditch effort?
it is a last ditch effort to maintain cerebral circulation (and regulate BP)
Brain Septae
protects against excessive brain tissue movement
help divide the brain and keep things where they should be
Falx Cerebri
sickle shaped brain septae
separates the two hemispheres of the brain (left and right)
Tentorium Cerebelli
divides the cranial cavity into anterior and posterior fossae (front and back)
Divides the brain from the cerebellum
brain septae
Incisura or Tentorial Notch
Large semicircular opening in the midbrain that occupies the anterior portion
Supra means…
tissue above the temporium
Infra means…
tissue below the temporium
Brain Herniation
displacement of brain tissue under the falx cerebri
or through the tentorial notch or incisura of the tentorium cerebelli
Herniation Syndromes
based on the area of the brain that has herniated and structure under which it has been pushed
Supratentorial herniation
Above the cerebellum and above the tentorium
Has different syndromes and they each have distinguishing features in early phases
What are the different Supratentorial Herniation Syndromes
Cingulate or Across the Falx Cerebri
Uncal or lateral
Central or Transtentorial
Common element between supratentorial herniation syndromes?
compression of the vasculature and CSF flow
All supratentorial syndromes have distinguishing features early on but ..
the clinical signs become more similar as the compression of the pons and medulla continues and pressure builds
What happens at the maximum point of ICP in supratentorial herniations?
The only place brain will be able to go is through the foramen magnum causing brain stem herniation, medullary herniation and compression and death
Cingulate Herniation
Type of Supratentorial herniation syndrome
Displacement of the cingulate gyrus and hemisphere beneath the sharp edges of the falx cerebri to the opposite side of the brain (so this is a herniation to opposite hemisphere - left or right)
Displacement compresses local blood supply and brain tissue –> this causes ischemia and edema –> this leads to increased ICP
Key S/S of Cingulate Herniation
Leg weakness can be seen - early sign
can progress to leg paralysis
The top of the brian is where the motor strip is so there would be consequences of motor activity
Uncal Herniation
Subtype of transtentorial herniation
A lateral mass pushes brain tissue centrally and forces medial aspect of the temporal lobe (containing the uncas and hippocampus gyrus) under the edges of the tentorial incisura and into the posterior fossa
Uncus
innermost part of temporal lobe
Increased ICP makes it move towaad the tentorium and put pressure on the brain stem
This especially happens on the mid brain
Also it puts pressure on CN III which controls pupil dilation which means there are eye issues
What are the CNIII (oculomotor) nerve and posterior cerebral artery caught between in uncal herniation?
the uncas and tentorium
Earliest sign of Uncal Herniation
Ipsilateral pupillary dilation from CNIII entrapment (same side)
Consciousness may not be affected, but deterioration proceeds rapidly
What are motor changes like in Uncal Herniation
ipsilateral changes in motor strength and coordination of voluntary movements d/t compression of descending motor pathways - HEMIPARESIS
occurs same side as herniation because its before the cross at medulla oblongata
Two Big Signs of Uncal Herniation are…
Ipsilateral pupillary dilation
ipsilateral motor changes
What are some late signs of Uncal herniation?
Bilateral positive Babinski sign and respiratory changes (Cheyne strokes, ataxic patterns)
Decorticate and Decerebrate Posturing
Dilated, Fixed pupils, flaccidity, and repsiratory arrest
Central Herniation
Downward displacement of cerebral hemispheres, basal ganglia, and midbrain through the tentorial incisura
Herniation is downward
What is different between Central and Uncal Herniation
Central is just downward moving but Uncal is in and down
What is the earliest sign of central herniation
Clouding/decrease in level of consciousness because of pressure on the RAS system for wakefulness
They may be confused and this is a sign of decreased LOC
Other Early signs of Central herniation
Clouding of Consciousness
Bilateral small pupils (2mm) with full range of constriction
Motor responses to pain that are purposeful or semi purposeful (localizing) and often asymmetric
Late signs of Central Herniation
Painful stimulation –> decorticate posturing which may be asymmetric
Waxing and waning of respirations with periods of apnea (Cheyne Stokes)
What are some late signs of midbrain involvement in a central herniation?
Fixed and mid-sized (5 mm) pupils, reflex adduction is impaired
Pain –> cerebrate posturing
Respirations –> neurogenic hyperventilation (40 bpm)
What are some late signs of Pons and Medullary involvement in Central herniation?
pupils –> fixed, midsize with loss of reflex eye adduction
Pain –> no motor response or only leg flexion occurs
Decorticate Posturing comes from damage where
to cortical structures in the anterior frontal area
Decerebrate posturing comes from damage where
to central structures like the midbrain
What is worse, decerebrate or decorticate posturing
decerebrate - damage occurred to more central structures that do automatic function
Infratentorial Herniation
Herniation that starts bellow the tentorial incisura and tentorium cerebelli – can go up through the incisura or down below the foramen magnum opening to the spine
Results from increased pressure in the infratentorial compartment
Tends to progress rapidly and can cause death
Infratentorial Herniations are more likely to involve what?
Lower brain stem centers that control vital cardiopulmonary functions
How can infratentorial herniations move?
- Superiorly (Upward) through the tentorial incisura
2. Inferiorly (Downward) through the foramen magnum
Superiorly Moving Infratentorial herniation leads to …
upward movement through the incisura –> blockage of aqueduct of sylvius –> hydrocephalus –> coma
Inferiorly Moving Infratentorial herniation leads to …
downward movement through the foramen magnum –> cardiac or resp arrest
What can happen if there is a pre existing increased ICP and a lumbar puncture is done?
Downward herniation can occur when pressure is released causing cardiac or respiratory arrest
A cingulate herniation looks like what?
herniation of brain tissue from right to left or left to right under the falx cerebri
An uncal herniation looks like what?
movement over and down toward the incisura
What does a transtensorial/downward herniation look like?
downward across the tentorium and pushes the tentorium
