Topic 5 - Extra cranial cerebral vessels and sub clavian

Question 1

What are the two main reasons patients are referred or a carotid ultrasound?

Answer 1

• To find a cause of TIA, stroke or amaurosis fugax when symptoms have already occurred.
• To find patients with stenosis who require endarterectomy or stenting before symptoms have occurred.
These patients are usually at high risk of carotid disease because of underlying cardiovascular risk factors or the presence of a bruit.

Question 2

What questions should you ask patients who attend for a carotid ultrasound who have symptoms?

Answer 2

• Have symptoms of numbness, tingling or weakness been experienced? If so, which side was affected and which part of the body?
• Has any visual disturbance been experienced? If so, which side was affected?
• Has speech been affected?
• Has vertigo occurred?
• Has memory been affected?
For any of the above, determine approximately
• how long the symptoms lasted
• how long since the symptoms occurred
• were multiple episodes of symptoms experienced (including duration and time between episodes).

Question 3

What questions should you ask patients who attend for a carotid ultrasound who do not have symptoms?

Answer 3

• A general indication of the type of risk factor is sufficient.
• Patients who are going to surgery for atherosclerosis in other arteries are often referred for carotid studies because of the association of atherosclerosis in multiple circulations.
• This is especially relevant for the patients undergoing coronary bypass surgery as there is a strong association between coronary and carotid disease.

Question 4

What are the three questions that need answering in a cerebrovascular ultrasound?

Answer 4

1. Which artery is the atheroma located in? (identifying carotid arteries)
2. What type of atheroma (or other pathology) is present? (Plaque characterisation)
3. How tightly does the disease narrow the artery? ( Degree of stenosis)

Question 5

How can you use the spectral waveform to assist in identifying the ECA?

Answer 5

ECA has a much steeper upstroke phase in systole and lower diastolic velocity when compared to the ICA but this is not always true. A temporal tap can also be elicited in the ECA however this is also true of the proximal ICA.

Question 6

Why is plaque characterisation used as a predictor of those who may be at high risk of TIA or stroke.

Answer 6

If the patient develops a high degree of stenosis, then the need for intervention is indicated.
However, not all patients with a high degree of stenosis will develop symptoms and patients with lesser degrees of stenosis may also experience symptoms.

Question 7

What are the two plaque characteristics that are assessed?

Answer 7

1. Plaque echogenicity

2. Surface characteristics

Question 8

What does a low echogenic plaque indicate?

Answer 8

Less echogenic than the surrounding muscle or absent B-mode texture (echolucent) with a thin fibrous cap.
This indicates a significant lipid core or haemorrhage which makes them more vulnerable to rupture and causing symptoms

Question 9

What does moderate echogenicity plaque indicate?

Answer 9

Less echogenic or equal echogenicity compared to surrounding muscle but less echogenic than the adventitia. This plaque relates to a greater content of collagen and fibrin.

Question 10

How are plaques with strong echogenicity described?

Answer 10

Greater echogenicity than the surrounding tissue and may show shadowing from calcification

Question 11

How are homogenous plaques described?

Answer 11

Plaque is uniform in echo texture and may be echolucent or echogenic. Plaque with echolucent regions are considered at higher risk of symptoms than plaque with calcified regions.

Question 12

What causes heterogeneous plaque?

Answer 12

Plaque contains various levels of echogenicity which may represent highly echogenic calcification or echolucent regions which may represent plaque haemorrhage.

Question 13

What is he significance of irregular plaque?

Answer 13

may represent the presence of ulceration
but can also indicate adjacent plaque formations
or an irregular plaque which is not ulcerated.
It is difficult and unreliable to confirm the presence of ulceration but in some cases the focal irregularity of a plaque is worth highlighting.

Question 14

Why is calculating the degree of stenosis important?

Answer 14

The degree of stenosis has the strongest relationship to the incidence of symptoms and increasing degrees of stenosis increase the risk of significant stroke

Question 15

• The European Carotid Surgery Trial (ECST) and the North America Carotid Endarterectomy Trial (NASCET) show?

Answer 15

that symptomatic patients with greater than 80% and 70% stenosis respectively will have a clear benefit from surgical endarterectomy.

Question 16

What did the ACAS study show?

Answer 16

• For patients without symptoms, has suggested benefit from surgery in patients with stenosis of greater than 60%

Question 17

When a lesion is not haemodynamically significant how is plaque graded?

Answer 17

Real-time imaging
• when blood flow velocities are less than 125 em/sec, then the percentage lumen diameter narrowing is subjectively estimated
• Although cross-sectional imaging in the transverse plane may offer better delineation of asymmetric and eccentric plaques, the physics of ultrasound make it difficult to resolve the edges of the more lateral aspects of the artery.
• Sizing of carotid plaque can be performed either by measuring the height or amount of thickening of the wall rather than by determining the residual lumen of the vessel.
• Direct measurements of plaque height (wall thickness) are now used for the evaluation of the response of atherosclerotic plaque to various therapies

Question 18

What is the special criteria NASCET?

Answer 18

NASCET and and ECST studies used angiography to estimate stenosis
afterward a number of studies were published which determined Duplex criteria to identify stenosis of greater than 70% (NASCET) and 80% (ECST).
the NASCET method is most commonly used in Australia

Question 19

What is the consensus criteria for normal carotid?

Answer 19

<125 psv
no bmode plaque
<40 EDV ICA
ICA/CCA psv <2

Question 20

What is the consensus criteria for 50-69% stenosis carotid?

Answer 20

50-59 b mode
>125
>40 EDV
ICA/CCA 2-4

Question 21

What is the consensus criteria for 70-89 % stenosis carotid?

Answer 21

70-89 b mode
>230 psv
>100 EDV
>4 ICA/CCA psv

Question 22

What is important to remember about bmode versus spectral calculation of stenosis?

Answer 22

• spectral criteria are not considered valuable for lesions under 50%
• B-mode measurement will allow an estimate of the ‘burden’ of atheroma present.
• It is also considered that B-mode and colour estimates of stenosis above 50% are not accurate and velocity criteria should be used.

Question 23

What is the ECA criteria for stenosis?

Answer 23

• difficult to identify in the literature
• can range from 150cm/s upward.
• At 150cm/s the incidence of false positive results will be high, so a higher value of about 180-200cm/s may be more appropriate assuming that it matches with visible atheroma in the artery.

Question 24

What is the criteria for vertebral artery stenosis?

Answer 24

• usually occurs at the origin
• difficult to determine.
• Typically the vertebral artery will have a velocity of up to 50cm/s
• The blood flow pattern should resemble that of the internal carotid artery.
• if the contralateral artery is hypoplastic or absent then the velocity in the ipsilateral artery can be substantially higher without indicating pathology.
• The best indication of vertebral artery stenosis includes a raised velocity with evidence of aliasing and reduced luminal diameter on colour flow

Question 25

What can an absent vertebral artery indicate?

Answer 25

• The vertebral artery may be vestigial and show a minor flow channel (trickle flow) or appear to be absent.
• An occluded vertebral artery may also appear absent, thus ‘non visualisation’ of a vertebral artery may indicate either a vestigial or occluded artery

Question 26

What does reverse flow of the vertebral artery indicate?

Answer 26

• A completely reversed pattern of blood flow is seen when the subclavian artery on the same side of the neck is occluded or has a severe stenosis

Question 27

What can indicate a proximal subclavian stenosis?

Answer 27

• Any period of flow reversal or sudden fall in velocity at any time in the vertebral artery spectral trace may indicate proximal subclavian stenosis and should be investigated.

Question 28

What is subclavian steal syndrome?

Answer 28

an example of a collateral pathway that develops in order to compensate for the effects of a proximal subclavian artery occlusion.

Question 29

What happens with left subclavian steal syndrome?

Answer 29

With a left subclavian artery occlusion, collateral flow is redirected from the opposite vertebral through the basilar artery to the subclavian artery distal to the occlusion.
On occasion, the collateral supply is through the circle of Willis.

Question 30

What happens with right subclavian steal syndrome?

Answer 30

The proximal occlusion involves the innominate artery. Blood flow is redirected from the opposite vertebral down the ipsilateral vertebral.
The vertebral then goes on not only to supply the subclavian artery but also the ipsilateral common carotid and then the internal carotid.
Blood flow in both systems is markedly reduced.

Question 31

What is the earliest change in vertebral artery waveform in subclavian steal syndrome?

Answer 31

the “bunny” sign since the contour resembles the silhouette of a rabbit.

Question 32

What PSV value is a good indicator of a haemodynamically significant lesion in the carotid?

Answer 32

• A peak systolic velocity above 125 em/sec

Question 33

Describe the ultrasound features which identify the carotid arteries

Answer 33

• Anatomic relationship – In most cases the ICA is lateral and posterior and the ECI is medial and anterior
• Branching – The ECA will show branches on colour investigation and the ICA will not
• Spectral waveform - ECA has a much steeper upstroke phase in systole and lower diastolic velocity when compared to the ICA but this is not always true. A temporal tap can also be elicited in the ECA however this is also true of the proximal ICA.

Question 34

What are parameters other than PSV that can be used to indicate stenosis?

Answer 34

• an elevated end diastolic velocity is a useful marker of a more severe stenosis
• The peak systolic velocity ratio is favoured as a diagnostic criterion over the end-diastolic velocity ratio.
• An end-diastolic velocity ratio above 2.4 is considered abnormal.
• the ratio of the peak systolic velocities between the right and left sides. This should normally be between 0.7 to 1 .3.

Question 35

What is the spectral appearance of a normal carotid?

Answer 35

mostly monophasic flow pattern
strong systolic and diastolic flow throughout the cardiac cycle.
The contour of the waveform tends to be smooth.
Peak systolic velocities are normally 80 to 100 em/sec in younger patients and 60 to 80 em/sec in older patients.

Question 36

Describe the flow patterns after an endarterectomy

Answer 36

• Disturbed (nonlaminar) blood flow patterns are commonly seen following endarterectomy.
• Caused by the loss of the normal endothelial lining and remodeling of the shape of the artery leads to a disruption of the normal laminar contour of blood flow near the arterial wall interface
as well as vorticeal, spiraling, and vorticeal blood flow patterns.
• This can cause an artificial elevation in the velocity of blood flow in parts of the artery lumen

Question 37

What are Ipsilateral effects of ICA stenosis on CCA?

Answer 37

PSV and EDV may decrease

strong evidence for the presence of a severe stenosis

Question 38

What are the ultrasound features of a stenotic jet?

Answer 38

• The stenotic jet can extend over distances of up to 2 cm
• The velocity of blood within this jet can be measured and used to estimate what the peak systolic velocity would be at the stenosis proper
• The jet tends to direct itself preferentially in one direction and to hit the wall of the carotid in the same spot.
• A zone of flow reversal normally starts to form just beyond the stenosis, around the stenotic jet
Appears as a jet of aliasing on colour doppler

Question 39

What is important to consider when imaging a high grade stenosis?

Answer 39

• A stenosis of greater than 95% diameter narrowing can cause the volume of blood flow through the diseased carotid artery to decrease to the extent that the peak systolic velocities also decrease.
• Measurement of the peak systolic velocity may therefore miss significant lesions
• A simple way around this problem is to look at the size of the color flow lumen.
• A small-diameter color (or power Doppler) lumen can help confirm this diagnosis.
• Depressed velocities in the internal carotid should suggest the possibility of a high-grade obstruction in the intracranial portion of the internal carotid
• especially when diastolic flow is depressed (high resistance pattern)

Question 40

How does an almost occluded ECA present on ultrasound?

Answer 40

• High-grade lesions of the external carotid artery can affect the velocity of blood in the ipsilateral internal carotid artery.
• The velocity of blood is artificially increased in the internal carotid since almost all of the blood flow from the common carotid artery is going into the internal carotid.
• This only becomes noticeable if the external carotid has a very high-grade stenosis close to a total occlusion

Question 41

How can common carotid artery occlusion change flow patterns?

Answer 41

• may cause retrograde flow in the external carotid artery and can involve retrograde flow in the superior thyroid artery.
• In some cases the superior thyroid artery may supply both the internal carotid and distal external carotid arteries.

Question 42

How can ICA occlusion change flow patterns?

Answer 42

• If the occlusion is proximal to the ophthalmic artery, there may be reverse flow in the ipsi-lateral ophthalmic artery with reverse flow in the supra orbital artery.
• Occlusion distal to the ophthalmic artery will not change the flow direction of the ophthalmic or other ipsi-lateral facial arteries.
• may result in extra blood flow in the contra-lateral carotid system, with a consequent increase in peak systolic velocity.

Question 43

What can a thickened intimal media thickness indicate?

Answer 43

• Individuals with increased wall thickness have more atherosclerosis in other arterial beds than those with thinner walls.
• Individuals with thicker walls are also more likely to have heart attacks or strokes than those with thinner walls.
• Thickening of the wall above 0.6 mm in a young population is thought to represent evidence of early atherosclerosis.
• Serial changes in IMT occur in response to either drug or dietary interventions
• Can be thickened by Takayasu arteritis and giant cell arteritis

Question 44

How do you define an ulcerated plaque?

Answer 44

An ulcer is defined as a cavity 2 mm wide by at least 2 mm deep in a carotid artery plaque

Question 45

What are the ultrasound features of arythmia?

Answer 45

• The ectopic beat is likely to show decreased blood flow velocity due to the transient decrease in cardiac output
• whereas the postectopic beat will be potentiated and have increased blood flow velocity

Question 46

What method should you use to determine a stenosis in a patient with arrythmia?

Answer 46

The use of the peak systolic velocity ratio is recommended specifically in patients who have a significant arrhythmia.
the peak systolic ratio from the highest common and internal carotid artery

Question 47

What are some masses that may cause carotid flow abnormalities?

Answer 47

• carotid body tumors
• hyperthyroidism
• rarely adenomatous nodules
• Passive displacement of the carotid by a soft tissue mass often creates the illusion that the artery itself is enlarged.

Question 48

What is the purpose of transcranial Doppler?

Answer 48

• identification of stenosis or vasospasm
• A-V fistula
• monitoring microemboli
• assisting with the identification of flow loss in brain death.

Question 49

1. List the presenting symptoms for a patient with subclavian steal syndrome.

Answer 49

Subclavian steal is usually an incidental finding during carotid and vertebral examination.
Patients are usually asymptomatic
- five percent will exhibit signs of ischaemia, such as pain, weakness, cold arm, and decreased pulse
- Clinically, the affected arm will demonstrate a decreased brachial and radial pulse.
- Patients will report difficulties with blood pressure measurements on the affected arm.
- There also may be decreased strength and pallor of the hand.

Question 50

List the possible diseases that might cause vertebrobasilar insufficiency.

Answer 50

• arteriosclerosis causing stenosis, occlusion, aneurysm;
• cervical trauma causing arterial dissection;
• subclavian steal syndrome;
• cardiac dysfunction;
• haemodynamic effects of carotid artery disease;
• vertebral artery ectasia; and
• vertebral artery impingement.

Question 51

How would you determine whether the patient’s symptoms related to carotid artery or vertebral artery disease in vertebrobasilar insufficiency?

Answer 51

not possible to be certain clinically - there is an overlap of symptoms;
• vertebral impingement - try to reproduce the patient’s symptoms, scan the vertebrals;
• ultrasound examination of the carotid and vertebral arteries; and
• transcranial examination of the vertebral and basilar arteries.

Question 52

List the symptoms for thoracic outlet syndrome.

Answer 52

• Neck, shoulder, arm pain
• Numb, cold arm and hand
• Pallor of the hand
• Decreased hand strength

Question 53

List the causes for thoracic outlet syndrome.

Answer 53

• Cervical rib
• Fibrous bands
• Trauma to shoulder region causing compression

Question 54

List he treatments for thoracic outlet syndrome.

Answer 54

• Physiotherapy to relax scalene muscles

* Surgery to remove cervical rib or fibrous bands or whatever is causing compression

Question 55

Briefly list the procedure to assess for entrapment of the subclavian artery from the thoracic outlet.

Answer 55

The patient is often best sat in a chair. Prior to scanning, the position of the arm in 0 deg, 45 deg, 90 deg. and 110deg. is explained. This is shown to them. Spectral waveforms are then recorded just lateral to the clavicle in the subclavian artery in each position. If there is a velocity increase or cessation of flow, the arm is moved to determine exactly what angle the entrapment occurs at.
The venous system in then assessed for thrombosis. It is also observed through this range of movement.
As this is often a bilateral anomaly, the contralateral side is also scanned. The diagnosis in generally a clinical one. Careful discussion with the patient about their symptom will assist you in determining the likelihood of this pathology.