Carotid Artery Ultrasound Examination
Evidence 2
Indication
Carotid artery pathologies are predominantly due to atherosclerosis disrupting
haemodynamic signature of cerebral flow. These generally present as
i)
ii)
iii)
iv)
v)
vi)
Transient ischaemic attacks
Amaurosis fugax
Impaired Coordination
Vertigo
Parasthesis , as well as
Non atherosclerotic lesions.
For this portfolio, I will focus on atherosclerotic changes of the intima.
Ultrasound is the modality of choice when examining the carotid arteries
because it is non-invasive and easily accessible. Ultrasound has advantage over
other modalities in its ability to examine both the haemodynamics of blood
flow within the artery as well as assessing critical plaque that might not cause
any haemodynamic significance. Traditionally, haemodynamic changes have
been used in the diagnosis, however assessing the intima for plaque
characterisation plays a very important part in diagnosis
Plaque Classification
ultrasoundpaedia
n
images of normal intima, smooth echogenic intima, with a hypoechoic intima
media. Thickness of equal or less than 0.9mm
Soft plaque low level echoes , smooth surface. May be undetected unless colour or power Doppler
is used.
Fibrotic plaque is thickened intima with echogenic non shadowing . This plaque is stable but needs
to be monitored
Complex plaque is significant plaque. It contains echogenic plaque with shadowing. This type of
plaque has an irregular surface. On colour Doppler, ulceration and necrosis is usually demonstrated.
Necrotic plaque has potential to dislodge and travel upstream resulting in patient’s symptoms.
Identifying the different types of plaque is diagnosis enough even if the stenosis does not result in
haemodynamic changes. When we find plaque, we need to determine the degree of stenosis it
causes. Measuring the residual lumen and pulse wave Doppler are methods used to evaluate the
degree of stenosis
Two trials , European and North American studies, using B Mode imaging evaluate the degree of
stenosis by measuring residual lumen
North American Symptomatic Carotid
Endarterectomy Trial
European Carotid Surgery Trial
Measures stenosis by comparing lumen diameter Measures stenosis by comparing overall
at level of stenosis to distal lumen diameter
diameter to residual lumen diameter at
maximum stenosis
Comparing diameters is also used to assess the degree of stenosis. This can be used in follow up
scans.
Pulse wave Doppler is used to demonstrate haemodynamic changes within the Carotid Artery that
occur due to plaque. Both flow velocities and type of waveform are diagnostic
Below is a table of diagnostic values (ASUM guidelines revised March 2008)
Stenosis Grade
0
< 15 %
18- 49 %
50-69%
70-79%
Pulse wave Doppler criteria
Normal waveform. No spectral broadening
Deceleration with spectral broadening PSV <125
cm/sec
Spectral broadening PSV < 125 cm/sec
Spectral broadening
PSV>125cm/sec EDV 110 cm/sec
ICA?CCA >2
Spectral broadening
PSV >270cm/sec EDV >110cm/sec
ICA/CCA >4
80-99%
Occlusion
Spectral broadening
PSV>270cm/sec EDV >140 cm/sec
ICA/CCA >4
No flow on colour and power dopplerTerminal
thump on pulse wave doppler
Signature pulse wave Dopplers
Common Carotid (CCA)
High resistance flow with prolonged diastolic flow. (Combination of both Internal and external
Carotid waveforms)
No spectral broadening
Internal Carotid
Low resistance flow
Prolonged flow in diastole
No spectral broadening
External Carotid artery
High resistance flow with low diastole
Prominent dichrotic notch compared to internal Carotid waveform
No spectral broadening
Severe stenosis in Internal Carotid artery
Above image shows very high Peak Systolic Velocity causing aliasing. Very high end dystolic velocity
with spectral broadening.
References
1 Hedrick, Wayne R., Davis Hykes L., and Dale Starchman E. Ultrasound Physics and instrumentation.
St Louis MO. Elsevier Mosby 2005.
2 Gill, Robert. The physics and technology od diagnostic ultrasound: A Practitioner’s guide.
Abbotsford N.S.W.:High frequency Publishing 2012
3 Myers, Kenneth A. and Amy clough. Making sence of vascular Ultrasound. A Hands on Guide.
London:Arnold 2004
4 Allan, Paull. P. clinical Doppler ultrasound [Oxford]: Churchill Livingstone/Elsevier. 2006