Occlusive atherosclerosis of the internal carotid artery (ICA) and secondary angiographic string sign

Findings

Figure 1: The left proximal common carotid artery demonstrates an atypical high-grade waveform, and a high resistance systolic upstroke. This waveform is more characteristic of the external carotid artery, and less like the internal carotid artery.
Figure 2: There is complete absence of flow in the left ICA and the ICA on grayscale appears completely occluded.
Figure 3 and Figure 4: Lateral views show the angiographic string sign. Early arterial phase images demonstrate a 99% stenosis of the proximal ICA. A trickle of contrast material is seen in the ICA distal to the stenosis.

Differential diagnoses
- String sign secondary to atherosclerosis at the proximal ICA and distal collapse of the ICA
- Dissection of the ICA
- Subacute/chronic thrombosis of the ICA
- Carotid artery stenosis secondary to radiation


Diagnosis: Occlusive atherosclerosis of the internal carotid artery (ICA) and secondary angiographic string sign


Atherosclerosis is the most common cause of the angiographic string sign. As the plaque enlarges, the pressure threshold for continued antegrade flow distal to the stenosis is reached. The distal ICA vessel lumen collapses as a result of decreased flow leading to the production of the string sign.

Carotid duplex ultrasound with color Doppler flow imaging and CT are first line diagnostic modalities for patients with symptomatic atherosclerotic vascular disease. When an occlusion of the carotid artery is seen, confirmatory imaging may be requested because differentiation between partial occlusion and a complete occlusion has important therapeutic implications.

The North American Symptomatic Carotid Endarterectomy Trial (NASCET) demonstrated a significantly decreased risk of stroke in patients with at least 70% stensoses, undergoing endarterectomy versus medical management (9% vs. 26%, respectively).