Dissection of the Internal Carotid Artery: Doppler Signs and Ultrasound Limitations
General Concepts of Dissection
Dissection is a tear in the intima with blood entering the vessel wall, forming a second (false) lumen separated from the true lumen by a detached intimal flap. The main ultrasound sign is a mobile echogenic membrane (detached flap) oscillating in sync with heartbeats, separating two lumens with different flow characteristics: in the false lumen, the flow is slowed, possibly turbulent or thrombosed. On color Doppler imaging (CDI), lumens often appear with different flow directions or intensities.
Doppler Signs of Dissection
According to sources, key findings in duplex scanning include:
| Sign | Characteristic |
|---|---|
| Detached intimal flap (membrane) | Mobile echogenic structure oscillating with the heart |
| Two lumens | True and false, separated by the flap |
| Flow characteristics in the false lumen | Slowed, turbulent, or thrombosed |
| CDI | Different flow directions or intensities in lumens |
Limitations of Ultrasound in ICA Dissection
Ultrasound examination has specific limitations described in sources related to vascular diagnostics in general. For instance, the accuracy of velocity measurements decreases with significantly calcified plaque; certain segments (aorta, common iliac arteries) may be obscured by intestinal gas. Some imaging modes do not display aliasing and flow direction, complicating interpretation.
Specifically for ICA dissection, the diagnostic accuracy of color duplex has been studied in separate works dedicated to recognizing spontaneous carotid artery dissection causing ischemia, as well as cases with isolated Horner syndrome. Specific sensitivity and specificity values are not provided in fragments [clarify].
Identification of ICA and Auxiliary Techniques
For reliable identification of the ICA and ECA, the tapping test on the superficial temporal artery (a branch of the ECA) is used: rhythmic oscillations ('sawtooth' pattern) appear on the diastolic part of the ECA spectrum, while the ICA does not respond to tapping. The external carotid artery is always described — this is a requirement of accreditation standards (IAC/SRU), as in the case of ICA or CCA occlusion, the ECA becomes a key collateral to the brain via the ophthalmic anastomosis.
Frequently asked questions
What is the main ultrasound sign of dissection?
A mobile echogenic membrane (detached intimal flap) oscillating in sync with heartbeats, separating true and false lumens.
What does the flow look like in the false lumen?
The flow in the false lumen is slowed, possibly turbulent or thrombosed.
What does CDI show in dissection?
Lumens often appear with different flow directions or intensities.
What ultrasound limitations are important to consider?
Significant calcification hinders accurate velocity measurements, some segments may be obscured by intestinal gas; some modes do not display aliasing and flow direction.
Has the accuracy of duplex in ICA dissection been studied?
Yes, separate studies focus on the accuracy of color duplex in spontaneous carotid artery dissection causing ischemia and cases with isolated Horner syndrome; specific figures are not provided in fragments [clarify].