Page 70 - Libro 2

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PART 2 — CEREBROVASCULAR
Vessel-Specific Abnormal Waveform Contours
“String sign” flow is characterized by blunted, some- what resistive waveforms and is the pattern that pre- cedes complete occlusion of the vessel (Fig. 4-20A,B). This is most likely to be found in a severely diseased ICA. It is important to differentiate string sign flow from complete vessel occlusion. With a string sign, the patient may still undergo an endarterectomy, whereas the patient with a completely occluded ves- sel will not be a surgical candidate. To aid in this dif- ferentiation, the vessels should be imaged along both the long axis and the transverse planes using color Doppler (with settings of low scale and high gain)
and power Doppler to detect the presence of any flow. Careful interrogation of the most distal extracranial ICA segment is important to avoid overlooking a pat- ent but small lumen in that location.
A markedly decreased diastolic flow or resistive component and overall “blunted” appearing wave- form in the extracranial ICA indicates a severe ste- nosis or occlusion in the more distal or intracranial segments (Fig. 4-21). This may be associated with severe distal extracranial ICA stenosis due to fibro- muscular dysplasia or segmental dissection. These changes will be observed even when there is a ste- nosis in the proximal ICA. Resistive and blunted flow
A
B
Figure 4-20 Duplex images of a functionally occluded inter- nal carotid artery with “string sign” Doppler flow. A: Use of color Doppler and spectral Doppler modalities. B: Use of color power angio modality.