Abstract:
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Purpose: Doppler sonography is used to reliably diagnose internal carotid artery stenosis, however, its ability to differentiate between pre-occlusive stenosis (> 95%) and complete occlusion remains controversial. The "string" sign and "trickle flow" are angiographic terms that have been applied to ultrasound findings. The aims of this study were (1) to define the term string sign as applied to carotid ultrasound and (2) to assess the ability of the "sonographic string" sign to differentiate between pre- and complete internal carotid artery occlusion.
Methods and Materials: 9219 carotid Dopplers were performed in our institution between 1998 and 2002. Of these, examinations reported as showing occlusion, 80-99% stenosis, or a "string sign" (n=526) were retrospectively reviewed by three radiologists blinded to the original interpretation. If a sonographic "string sign" was present, the "string" was further assigned to one of three categories; long, short or pseudostring. "Long" was defined as a color channel that extends throughout the visualized portion of the ICA. "Short" was defined as a color channel extending £ 2 cm from the carotid bifurcation. A "pseudostring" was defined as color seen intermittently in a non-contiguous pattern throughout the ICA. The sonographic diagnosis was then correlated with the angiographic findings.
Results: 30 patients were identified as having a "string sign". There were 9 long, 16 short, and 5 pseudostrings. Angiographic correlation of the 9 long strings yielded 8 pre-occlusions and 1 complete occlusion. The 16 short strings yielded 15 complete occlusions and 1 pre-occlusion. The 5 pseudostrings yielded 5 complete occlusions. The sonographic "long string" correlates best with the original angiographic terminology (sens 90%, spec 94%). The sonographic "short string" (sens 94%, spec 90%) and the sonographic "pseudostring" (sens 100%, spec 100%) should be interpreted as representing complete occlusion.
Conclusion: This study highlights the need to clarify the term "string sign" when applied to carotid ultrasound. The long string represents true trickle flow indicative of a pre-occlusive stenosis. We postulate that the short string on carotid Doppler is due to pulsatile erosion of the occluded stump. We believe the pseudostring is due to motion artifact associated with the low PRF/reduced wall filter selected for optimising slow flow visualization. Routine use of these terms should improve the accuracy of carotid Doppler ultrasound to differentiate between pre-occlusion and complete occlusion.
Questions about this event email: p_obrien70@yahoo.com
O'Brien MD, P,
The Sonographic "Carotid String" Sign: Long or Short?. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3107948.html
