Introduction 

Four arteries, the internal carotid and vertebral arteries on each side supply the brain. Ultrasound has a good access to the extracranial portion of these vessels.

 Mechanism

 Ischaemia from severe stenosis due to atherosclerotic disease involving the extra-cranial vessels is implicated in 30% of strokes. Atherosclerosis usually involves the proximal ICA and carotid bulb. 80% of strokes are thrombo-embolic in origin; often the carotid plaque is the embolic source.

Risk Factors

Hypertension

Diabetes

Myocardial Infarction

Smoking

Hypercholesterolemia

Atrial fibrillation

Alcohol

CCF 

Indications for carotid Doppler 

Presence of carotid bruit in an asymptomatic patient

CVA/ Stroke (loss of motor, sensory or cerebral function)

TIA (loss of function for less than 24 hours)

Vertebro-basilar symptoms (vertigo, ataxia, diplopia)

History of peripheral vascular disease, atherosclerosis 

Basic Anatomy

 The left CCA originates from the arch of aorta. Right CCA originates from the brachiocephalic artery. CCA runs cephalad, lying lateral to the ipsilateral thyroid lobe and medial to the IJV. The ECA is antero-medial, and has multiple branches. The ICA is postero-lateral; it has an increased diastolic flow when compared to ECA.

Flow Pattern

Laminar flow is seen in the normal carotid arteries, as seen in variations in color from center to periphery; slower velocities near the vessel wall are bright red while higher velocities in the center are lighter shades of red. This pattern indicates that most of the blood cells are moving at similar velocities. The “window” pattern seen in the Doppler spectrum of a normal carotid artery is due to laminar flow. Disturbance of this laminar flow usually occurs at the carotid bulb.

In the CCA and ICA, color persists on the Doppler image throughout the cardiac cycle because blood flow in these vessels is continuous throughout diastole, while flow in the ECA ceases or is markedly diminished during diastole.

Thus the spectral pattern is such:

ICA and CCA exhibit low pulsatility features consisting of broad systolic pulses and forward flow during diastole, while the ECA displays high pulsatility features, including a narrow, sharp systolic peak, and no flow / reversal of flow in diastole (look above).

 Carotid Interpretation

Vessel wall thickness: more than 0.8 mm is considered abnormal

 Plaque characterization: extent, location, surface contour and texture, ulceration

Plaque inhomogenecity is also considered a useful feature because it has been associated with intra-plaque hemorrhage, which in turn are related to intimal inflammation, ulceration, and rapid enlargement of plaque.

Evaluation of stenosis: in transverse plane

Plaque composition

Fibrofatty plaques, which contain a large amount of lipid material, are the least echogenic of plaques; echogenecity of plaques increases with collagen content.

Criteria for diagnosis of ICA disease

Some sonologists give a diameter narrowing as criteria for stenosis, some give a combination of PSV and diameter.

Vertebral Arteries

Important collateral pathway in carotid artery stenosis

The PSV is usually 0.2 to 0.5 m/s

Maximum diameter is usually not > than 4 mm, and not less than 2 mm.

Increased resistance is suggestive of intrinsic vertebral aertery disease

Failure to visualize a vertebral artery could indicate that the vessel is occluded, but more often than not, it could be a false-positive finding due to poor visualization / poor image quality.

Subclavian steal phenomenon:

Results from a stenosis of the subclavian artery proximal to the origin of the vertebral artery. The main direct sign of the steal phenomenon is reversed blood flow in the ipsilateral vertebral artery.

Conclusion

Stenosis, plaques, hemodynamic flow disturbances can be graded accurately and non-invasively by color Doppler.

Compiled with inputs from

Dr. Rahul Sachdev (Delhi), Dr. Alpana Joshi (Mumbai), Dr. Sanjeev Mani (Mumbai)

To be Concluded…..Troubleshooting Tips in Carotid Doppler