Module 3 : Intracranial Arteries Flashcards
(132 cards)
1
Q
how is doppler ultrasound use to asses cerebral hemodynamics
A
- measures blood flow velocities in the basal vessels in the circle of willis
2
Q
what must be known before performing TCD
A
- status of the extra cranial vessels
3
Q
what type of pulse wave doppler is used with TCD
A
- range gated [ulsed wave doppler
4
Q
what is non imaging PW doppler with a spectral analyzer used for
A
- excellent signal to noise ratio, lower bandwidth
- variable focusing depth, transmit power, adjustable gate depth
5
Q
is TCD or TCI more portable
A
- TCD
6
Q
what is the most common pitfall of TCD
A
- misidentification of vessels
7
Q
what y parameters aid in the identification of vessels with TCD
A
- depth of insonation
- flow velocity
- direction o fbeam angle
- response to carotid compression
- direction of flow
- probe position
- traceability of vessels
8
Q
what is TCI (TCCD) imaging
A
- adds imaging and uses color flow to act as a guide during the TCD exam
- also allows placement of sample volume
9
Q
what decreases doppler sensitivity with TCI
A
- larger footprint
10
Q
what type of doppler is preferred with TCI imaging
A
- power doppler Duttons to increased sensitivity and angle independence
11
Q
what is the most common application of TCD
A
- serial monitoring of MCA and other vessels for vasospasm
12
Q
what are 9 other applications of TCD/ TCI imaging
A
- monitor vasospastic effect of sickle cell anemia
- detect intracranial stenosis and occlusion
- adjunct to extra cranial and carotid duplex stenosis
- asses collateral circulation
- functional reserve testing
- evaluate intracranial aneurysm and AV malformation
- confirm brain death
- intraoperative monitoring
- detect right to left cardiac shunts PFO
13
Q
what are 5 limitations to TCD
A
- recent eye surgery may eliminate trans orbital approach
- no window or bone to thick
- inaccurate identification of vessels with TCD
- patient compliance
- technical expertise
14
Q
what are the 3 segments of the internal carotid artery
A
- cervical ICA
- Petrous ICA
- cavernous ICA (carotid siphon)
15
Q
where is the location of the cervical ICA
A
- carotid bifurcation to the carotid canal of the petrous portion of the temporal bone
16
Q
where is the location of the petrous ICA
A
- runs through petrous portion of the temporal bone
- not visualized with ultrasound
17
Q
what are the three portions of the cavernous ICA
A
- parasellar portion (prox segment)
- genu portion (bend)
- supraclinoid portion (distal segment)
18
Q
what is the first major branch of the ICA and what portion of the ICA does it arise from
A
- ophthalmic artery
- cavernous portion of the ICA
19
Q
what two vessel bifurcate from the terminal ICA
A
- anterior cerebral artery
- middle cerebral artery
20
Q
how many congenital malformations of the circle of willis are there
A
- at least 9
21
Q
what is the most common variations
A
- involve the communicating arteries
22
Q
what is the size of the circle and where is it located
A
- 3cm
- base of the brain
23
Q
are velocities in the circle of willis faster in the anterior or posterior circulation
A
- anterior (ICA distribution)
24
Q
which vessel carries the majority of the flow
A
- MCA
25
rank the velocities in the vessels from highest to lowest
MCA>>ACA>>PCA>>BA>>VERTS
26
do velocities in the circle of willis increase or decrease with age
- decrease
27
what percentage of population have an intact and functioning circle
- 50%
28
what percentage of population have the classic circle configuration
18-25%
29
what is the course of the MCA
- laterally towards the temporal bone with several branches
30
what are the 2 segments of the MCA and what are their locations
- M1= form MCA origin to first branch
| - M2= MCA distal to first branch
31
what is normal velocity range of MCA
- <90
| - usually 55 +/- 12
32
what are the 2 segments of the ACA and what are there course
- A1 = course medially towards the midbrain
| - A2 = course anteriorly to supply anterior segments of the brain
33
what vessel does the ACA give rise to
- anterior communicating artery which runs between the two ACAs
34
what is the purpose of the posterior cerebral artery
- perfuse posterior hemispheres
| - wrap around cerebral peduncles
35
what are the 2 segments of the PCA and what are there course
- P1 = origin to the posterior communicating artery
| - P2 = distal to PCoA
36
which vessel arises from P1
- posterior communicating artery
37
what is the purpose of PCoA
- connects to the anterior circulation and is a route for collateralization
38
what vessel do the vertebral arteries arise from
- subclavian arteries
39
what is the course of the vertebral arteries
- course between the transverse processes of the spine
| - enter the skull at the foramen magnum
40
what are the two intracranial branches of the vertebral artery
- anterior spinal artery
| - posterior inferior cerebellar artery
41
what is the basilar artery formed by
- two intracranial vertebral arteries
42
how long is the basilar artery
3cm
43
what does the basilar artery bifurcate into
tow posterior cerebral arteries
44
what vessels allow for cross filling and collateralization when an ICA obstruction is present
- ACoA
| - PCoA
45
what happens in patients with a nonfunctioning circle if an ICA obstruction occurs
- more significant neurologic ischemia
46
what are the four different approaches or windows to allow insonation of the arteries and what is the assumed angle of insonation
- transtemporal
- transorbital
- transforamenal/suboccipital
- submandibular (uncommon)
- 0º
47
What is the TCI imaging method
- noninvasive imaging of the intracranial arteries with color
- determines whether there is flow in the vessel
- real time
48
how is vessel identification done with TCD
- probe portion and beam angle
- depth of vessel
- flow direction
- traceability of vessel
- mean velocity value
49
what are the two different mean velocities with TCI imaging
- time averaged mean velocity
| - time averaged peak velocity
50
what is the time averaged mean velocity
- used for flow volume calculation
| - when the mean velocity calculation is displayed they'll be a line running through the middle of the waveforms
51
what is the time averaged peak velocity
- used in TCD and TCI
- not refereed to as mean velocity, MEAN OF THE PEAK VELOCITY OVER TIME
- all TCD velocity values are mean velocities
52
what does "mean" mean
- mean of the peak velocities over time referred to as TAMX
53
what is the most promising TCD/TCI window
- transtemporal
54
what vessels are being interrogated when an anterior angulation of 6º is used from the trans temporal window
- MCA, portion of carotid siphon, ACA, ACoA
55
what vessels are being interrogated when an posterior angulation of 5º is used from the trans temporal window
- PCA, basilar artery, PCoA
56
what is the insonation depth, flow direction, and velocity from the transtemporal window in the MCA
- 30-60mm
- antegrade flow
- 55cm/sec
57
what is the insonation depth, flow direction, and velocity from the transtemporal window in the MCA/ACA bifurcation
- 55-65mm
- bidirectional flow
- 50cm/sec
58
what is the insonation depth, flow direction, and velocity from the transtemporal window in the ACA
- 60-80mm
- retrograde flow
- 50cm/sec
59
what is the insonation depth, flow direction, and velocity from the transtemporal window in the ACoA
- 70mm
| - flow direction is present dependant on collateralization
60
what is the insonation depth, flow direction, and velocity from the transtemporal window in the PCA P1
- 60-70mm
- antegrade flow
- 40cm/sec
61
what is the insonation depth, flow direction, and velocity from the transtemporal window in the PCA P2
- 65-70mm
- retrograde flow
- 40cm/sec
62
what is the insonation depth, flow direction, and velocity from the transtemporal window in the PCoA
- only if fiction
| - not routinely assessed
63
what is the insonation depth, flow direction, and velocity from the transtemporal window in the TICA
- 55-65mm
- antegrade flow
- 39cm/sec
64
what are the 3 potential locations of the transtemporal windows
- posterior
- middle
- anterior
65
where is the probe placed for the trans orbital window
- probe situated medially on closed eyelid
66
what is the insonation depth, flow direction, and velocity from the transorbital window in the ophthalmic artery
- 40-60mm
- antegrade flow
- 21cm/sec
67
what is the insonation depth, flow direction, and velocity from the transorbital window in the 3 segments of the carotid siphon
- depths 60-80mm
- paraseller = antegrade, genu=bidirectional, supraclinoid= retrograde
- 47cm/sec
68
what technical parameter must be adjusted when scanning through the transorbital window
- power should be reduced to prevent damage to the eye and scanning time should be limited
69
what is the probe placement for the transforamenal window
- midline approach, angulation right to left
70
what is the insonation depth, flow direction, and velocity from the transforamenal window in the vertebral window
- 60-90mm
- retrograde flow
- 38cm/sec
71
what is the insonation depth, flow direction, and velocity from the transforamenal window in the basilar artery
- depth >80mm
- retrograde flow
- 40cm/sec
72
what vessels are interrogated from the submandibular window
- extradural segments of the distal ICA and carotid siphon
73
what is the insonation depth, flow direction, and velocity from the submandibular window in the extradural segments of the distal ICA and carotid siphon
- 80mm
- retrograde flow
- 30cm/sec
74
what do the vessels do with the collateral pathway through the ACoA on the normal side
```
MCA= toward, normal
ACA = away elevated
PCA P1 = toward, normal
PCA P2 = away, normal
BA = away normal
```
75
what do the vessels do with the collateral pathway through the ACoA on the diseased side
```
MCA = towards, normal/increased
ACA = toward, turbulent
PCA P1 = towards, normal
PCA P2 = away, normal
BA = Away normal
```
76
what do the vessels do with the collateral pathway through the PCoA on the normal side
```
MCA = toward normal
ACA = away elevated
PCA P1 = toward normal
PCA P2 = away normal
BA = away, elevated also expect elevated VA's
```
77
what do the vessels do with the collateral pathway through the PCoA on the diseased side
```
MCA= toward, normal/increased
ACA=toward turbulent
PCA P1 = toward elevated
PCA P2 = away normal
BA = away, normal
```
78
what do the vessels do with the collateral pathway through the OA on the normal side
```
MCA = toward normal
ACA = way normal
PCA P1= toward normal
PCA P2 = away normal
BA = away normal
```
79
what do the vessels do with the collateral pathway through the PCoA on the diseased side
MCA = toward, velocity dependant on capability of OA flow
ACA = toward, velocity dependent on capability of OA flow
PCA P1 = toward normal
PCA P2 = away, normal
BA = away, normal
80
what are the 11 clinical applications of transcranial doppler
- intracerebral aneursym
- intracranial stenosis/occlusion
- extra cranial stenosis/occlusion
- AV malformation
- intraoperative monitoring
- vasospasm
- brain death
- functional reserve testing or vasomotor reactivity
- screening patients with sickle cell anemia
- emboli detection
- PFO
-
81
what does aneurysmal disease result from
- wakening fo the structural proteins within the media
82
what can large aneurysms have a risk of
- constricting surrounding arterial flow
- rupture
- subsequent subarachnoid hemorrhage
- cerebral infarct
83
what is the most common site for intracranial aneurysm
- ACoA
| - especially when associated with SAH
84
what are two other common sites of intracranial aneurysms
- PCoA
| - MCA bifurcation
85
what will stenosis look like in transcranial doppler
- large basal arteries show increased velocity, disturbed flow with increased spectral broadening and co-vibration phenomenon
86
what are the pitfalls of evaluating for stenosis intracranially
- changes can be due to collateral flow or vessels supplying AVM's
87
what will occlusion look like in transcranial doppler
- absence of arterial signal at expected depth, patent communicators, and altered flow in communicating vessels
88
what are the pitfalls of evaluating for occlusion intracranially
- inadequate temporal window causing non visualization, displacement of vessel form its normal position by a tumor
89
how is patency of the circle of willis performed
- tested with compression or oscillation maneuvers
90
how is compression used to asses circle of willis
- application go slow pressure to CCA for 2-4 cardiac cycles with slow release, noting changes to flow direction and velocity
91
how is oscillations used to asses circle of willis
- short, rapid incomplete compressions, note transmitted oscillation
92
how are velocities in collaterals affected by contralateral CCA compressions
- already increased velocities accentuated
93
what are 3 different collateralization pathways
- crossover/right to left
- external to internal
- posterior to anterior
- vertebrobasilar
94
what is the crossover/right to left pathway
- antegrade flow is evident in ipsilateral ACA
- due to flow in patent ACoA
- increased velocities >150% in contralateral ACA are seen
- MCA velocities decrease with contralateral CCA compression
95
what is the external to internal pathway
- retrograde flow is seeing the ipsilateral ophthalmic artery
- due to flow form ECA branches that communicate with ophthalmic
- confirmed by noting reduction, obliteration, reversal of opthalmic flow with ipsilateral ECA compression
96
what is the posterior to anterior pathway
- flow velocities in ipsilateral PCA exceed that of the MCA by 125%
- increased flow velocities with compression of the CCA confirm this finding
97
what is the vertebrobasilar pathway
- circulation abnormalities due to subclavian steal are uncommon
- basilar artery flow may be reduced or show a "to and fro" pattern if both vertebral arteries are diseased
- revered flow is rarely seen
- subclavian steal is a benign condition
98
what will arteries look like with an AV malformation AVM
- increased systolic and diastolic velocities
- adjacent arteries have decreased flow
- reduced pulsatility
- velocities as high as 280
- little response to CO2 stimulation
99
what is intraoperative monitoring
- monitoring blood flow during endarterectomies and bypass surgery
100
what does intraoperative monitoring detect
- rapid changes in flow which alert surgeon to possible complications that alter operative technique
101
which vessel is monitored with intraoperative monitoring
- MCA giving information about cerebral perfusion
102
what MCA velocity indicates adequate collateral flow during intraoperative procedure
> 10cm/sec
103
what is the most frequent application of transcranial doppler
- detecting vasospasm
104
what is a spasm of cerebral arteries a complication of
- subarachnoid hemorrhage
105
where does a SAH occur
- between the arachnoid and Pia mater layers of the cerebrum
106
are vasospasms asymptomatic or symptomatic
- mild can be asymptomatic, but severe reduces cerebral perfusion and symptomatic ischemic deficit can result
107
what are the symptoms of vasospasm
- confusion
- decreased levels of consciousness
- stroke
108
where do vasospasms occur relative to the aneurysmal side
- can occur ipsilateral or contralateral to the side of the aneurysm or bilaterally
109
when does vasospasm usually occur
- 4-14 days post hemorrhage
110
what does an MCA velocity >120cm/sec indicate
- reaction to a documented hemorrhage
111
what does an increase of >20cm/sec per day in the MCA velocity indicate
- poor prognosis
112
what is an MCA velocity >200cm/sec associated with
- critical reduction in cerebral blood flow
113
what is an alternative method of diagnosis of vasospasm
- angiography
114
what three things is the determination of brain death is based on
- clinical status
- EEG results
- angiographic demonstration of absent intracranial circulation
115
what does spectral signals progressing toward brain death show
- decrease in diastolic flow
| - eventually reaching zero
116
what will signals show just prior to brain death
- reversed flow with a to and fro motion that is easily detected on a TCD spectral tracing
117
how does systolic velocity change with brain death
- decreases to the end result of no flow in the brain
118
what is functional reserve testing
- evaluates the reserve mechanism of cerebral vasculature in the presence of carotid occlusive disease using O2 stimulus
119
what vessel is monitored with functional reserve testing
- MCA
120
what is the normal response to functional reserve testing
- peripheral vascular bed should dilated in response to hypoxia and flow in MCA should increase
121
what is the abnormal response to functional reserve testing
- no change with CO2 stimulus this indicates peripheral beds are already maximally dilated therefore exhausting the vasomotor reserve
122
what is sickle cell anemia
- genetic defect of hemoglobin synthesis
| - sickle shaped RBCs clump together
123
what are patients with sickle cell at risk for
- strokes
124
what vessel velocities are investigated with sickle cell anemia
- MCA velocities
125
what MCA velocities indicate risk of stroke with sickle cell anemia
- >200cm/sec
| - patient should receive transfusions
126
what is emboli
- particulate matter can arise from carotid system plaque, heart tumors, or thrombus
- air emboli can occur during operative procedures
127
what is emboli detection also called
- micro emboli signals, or high intensity transient signals
128
what value is considered serious for emboli detection increasing risk of stroke
- >50HITS over a 10 minute period
129
what are three criteria for emboli detection
- duration usually <300cm/sec
- unidirectional signal within the doppler velocity spectrum
- signal is accompanied by snap or chirp on the audible output
130
what is a patent foramen ovale PFO
- abnormal right to left blood shunts in the heart that bypasses the pulmonary artery and lungs
131
what is a potential complication from PFO
- potential for venous thromboemboli ending up in the peripheral arterial system or in the cerebral vasculature
132
how does TCD detect PFO
- micro for bubbles are injected into a superficial vein in the arm during bilateral monitoring of the MCA blood flow
- foramen ovale is closed the bubbles fo to the lungs
- foramen ovale is open the bubbles will cause HITS in the MCA after a few seconds
