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According to this review article, for symptomatic internal carotid artery stenosis:

[Carotid endarterectomy] was highly beneficial in participants with 70% to 99% stenosis without near-occlusion (N = 1095, RR 0.47, 95%CI 0.25 to 0.88). However, there was no evidence of benefit (N = 271, RR 1.03, 95%CI 0.57 to 1.84) in participants with near-occlusions

Why is carotid endarterectomy beneficial for 70%-99%, but not 100% stenosis (unsure if this is the correct term)?

Source: Orrapin S, Rerkasem K. Carotid endarterectomy for symptomatic carotid stenosis. Cochrane Database Syst Rev. 2017 Jun 7;6(6):CD001081. doi: 10.1002/14651858.CD001081.pub3. PMID: 28590505; PMCID: PMC6481587.

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  • I don't think that review says anything about "symptomatic complete internal carotid occlusion", the group is "near-occlusions" which says nothing about symptomatic (nor is it truly complete if it's a near-occlusion).
    – Bryan Krause ♦
    Sep 22, 2020 at 19:33
  • I do admit I have confusion between the terms 99% stenosis, complete occlusion, and near-occlusion. Let me reword the question.
    – D.Tan
    Sep 22, 2020 at 19:35
  • If you look at the review article, it is specifically looking at symptomatic carotid stenosis. I think asymptomatic stenosis has a different treatment recommendation.
    – D.Tan
    Sep 22, 2020 at 19:38
  • Oops, yes you are right about only symptomatic. There was one sentence that made me think both were included. Near-occlusions are those where the vessel appears occluded and yet tracer passes through slowly.
    – Bryan Krause ♦
    Sep 22, 2020 at 19:43
  • A detailed description of how "near occlusion" is defined and what radiologic procedures are used to diagnosis it appears here. radiopaedia.org/articles/carotid-near-occlusion?lang=us As explained at this website, synonymous terms are "near-total occlusion, pseudo-occlusion, subocclusion, incomplete occlusion, functional occlusion, and preocclusive stenosis." So near-occlusions are not 100% occlusion. This doesn't answer your question but perhaps the findings of this pooled analysis don't seem so contradictory recognizing this.
    – Diana Petitti
    Sep 23, 2020 at 21:31

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I think this is probably due to selection bias, but I cannot find a source from someone in the field to reference.

Instead, to support this conclusion, note that in the review you reference, the people with near-occlusions overall have fewer negative outcomes than those with lesser occlusions.

People who are not already dead while having such a blockage clearly have enough collateral circulation to compensate for the near-occlusion. Something that is already blocked cannot become suddenly blocked in the future.

The review also mentions that these are all intent-to-treat analyses, and so it's not necessarily the case that those with near-occlusions did end up having surgery after all, despite being allocated to the non-surgery group. However, the lower (rather than higher) risk in this group seems to argue against that.

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