Topic 5 Extracranial cerebral and subclavian arteries

Question 1

Why are carotid ultrasounds commonly performed?

Answer 1

• find the cause of a TIA, stroke, amaurosis fugax when symptoms have already occured
• find patients with a stenosis who require endarterectomy or stenting before symptoms occur. These are patients at high risk of underlying cardiovascular disease

Question 2

Describe low echogenicity plaque

Answer 2

• Less echogenic than surrounding muscle
• Absent b-mode texture with a thin, fibrous cap
• indicates a significant lipid core or haemorrhage, which makes them vulnerable to rupture

Question 3

Describe moderate echogenicity plaque

Answer 3

• less echogenic or equally echogenic compared to surrounding muscle
• less echogenic than the adventitia
• plaque relates to greater content of collagen and fibrin

Question 4

Describe high echogenicity plaque

Answer 4

• Greater echogenicity than surrounding tissue

- may have shadowing from calcifications

Question 5

Describe the different surfaces of plaque

Answer 5

Plaque can be smooth or irregular. The presence of irregular surface can represent the presence of ulceration. Irregular surfaces can also indicate adjacent plaque formation, or plaque that is not ulcerated. It is difficult and unreliable to confirm the presence of ulceration. Focal irregularity is worth highlighting

Question 6

What is the importance of the degree of stenosis?

Answer 6

Increasing degree of stenosis = increasing risk of stroke. Degree of stenosis and presence of symptoms can help the doctor determine whether medical management or surgical intervention is required

Question 7

Define a stenosis

Answer 7

Stenosis is the reduction in diameter of the lumen

Question 8

What is the NASCET duplex criteria?

Answer 8

<50% stenosis:

• <125cm/s
• <50% plaque on b-mode
• ICA EDV <40cm/s
• ICA/CCA ratio <2

50-69% stenosis:

• > 125cm/s
• > 50% plaque on b-mode
• ICA EDV 40-100cm/s
• ICA/CCA ratio 2-4

> 70% - near occlusion:

• > 230cm/s
• > 50% plaque on b-mode
• ICA EDV >100cm/s
• ICA/CCA ratio >4

Near occlusion:

• High, low or absent velocity
• Plaque visible, lumen present

Occlusion:

• No velocity
• Plaque visible, no detected lumen

Question 9

Describe the ECA criteria for stenosis

Answer 9

• Velocity ranges from 150cm/s upwards (180-200cm/s)

Question 10

Describe vertebral artery criteria for stenosis

Answer 10

• Atherosclerotic stenosis usually occurs at the origin of the vertebral artery
• typically the velocity will be up to 50cm/s
• contralateral artery can be hypoplastic or absent, so the high velocity may not indicate pathology
• best indication for vertebral artery stenosis includes raised velocity with evidence of aliasing and reduced luminal diameter

Question 11

What is a primary collateral?

Answer 11

Primary collaterals provide immediate diversion of cerebral blood flow to ischaemic regions through existing anastomosis

Question 12

What can common carotid occlusion cause?

Answer 12

Retrograde flow in the ECA and can involve retrograde flow in the superior thyroid artery.

Question 13

What happens if the ICA is occluded proximal to the opthalmic artery?

Answer 13

There may be retrograde flow in the ipsilateral opthalmic artery and retrograde flow in the supraorbital artery

Question 14

What happens if the ICA is occluded distally to the opthalmic artery?

Answer 14

This will not change the direction of the opthalmic or other ipsilateral facial arteries.

Question 15

What are some clinical indications for transcranial ultrasound?

Answer 15

• identify a stenosis or vasospasm
• AV fistula
• monitoring of microemboli
• assisting with identification of flow loss in brain death.