# NASCET — NASCET carotid stenosis measurement

> Quantifies internal carotid artery stenosis severity.

**Situação:** vigente · **Órgão:** Vascular · **Órgão emissor:** NASCET investigators · **Versão:** 1991 · **Ano:** 1991

## Procedência e vigência
- Família: léxico
- Tipo de lógica: flat
- Modalidade: CT, MRI, US
- Fonte primária: North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade stenosis (NASCET) (1991) — https://doi.org/10.1056/NEJM199108153250701
- Última verificação: 2026-06-26
- Última checagem: 2026-06-26

## Categorias

| Código | Rótulo | Critérios | Conduta | Risco | Localizador | Verificado |
| --- | --- | --- | --- | --- | --- | --- |
| <50% | Mild stenosis | Mild internal carotid artery stenosis by the NASCET method — a NASCET-derived diameter reduction of 0-49%. NASCET quantifies stenosis by comparing the narrowest residual luminal diameter at the stenosis to the diameter of the normal distal cervical internal carotid artery (ICA) well beyond the bulb, where the walls are parallel and unaffected by plaque: percent stenosis = (1 - [minimal residual luminal diameter / diameter of normal distal ICA]) x 100. In the trial this band gained no significant benefit from carotid endarterectomy. | In symptomatic patients this degree of stenosis was found to derive no significant benefit from carotid endarterectomy (medical/best-medical management). | Lowest stroke risk of the symptomatic bands; surgery did not significantly reduce ipsilateral stroke and in the lowest-stenosis (<30%) subgroup CEA tended to be harmful (pooled 5-year RR ~1.25 for stroke/operative death), so the risk-benefit favours medical therapy. | Severity band from ESCR consensus (PMC9889495), 'Quantifying the degree of stenosis': 'According to NASCET, luminal stenosis is classified as "mild" (0-49%), "moderate" (50-69%), and "severe" (70-99%).' NASCET formula/measurement points from same section and from Wikipedia 'Carotid artery stenosis' Diagnosis section. 'No significant benefit <50%' and 'surgery tended to be harmful in participants with less than 30% stenosis' (RR ~1.25) from the Cochrane/CEA synthesis PMC6481587/PMC8536099 and StatPearls 'Carotid Endarterectomy' (NBK470582), Indications section. | ✓ |
| 50-69% | Moderate stenosis | Moderate internal carotid artery stenosis by the NASCET method — a NASCET-derived diameter reduction of 50-69% (measured by the same residual-lumen-vs-normal-distal-ICA ratio described for the <50% band). | Symptomatic patients with 50% or more ipsilateral stenosis plus a history of ipsilateral stroke or TIA are, per practice guidelines derived from NASCET, candidates for carotid endarterectomy; benefit in the moderate (50-69%) group is smaller than in the severe group. | Moderate stroke risk with modest surgical benefit. In NASCET, the 5-year risk of ipsilateral stroke for symptomatic 50-69% stenosis was about 15.7% with CEA versus 22.2% with medical therapy (absolute risk reduction roughly 6.5 percentage points, a ~29% relative reduction; number-needed-to-treat about 15). In pooled trial data the moderate band gave only a small benefit (5-year RR ~0.84). Benefit is therefore real but smaller than in the severe band and sensitive to surgical risk. | Severity band from ESCR consensus (PMC9889495), 'Quantifying the degree of stenosis' ('moderate' = 50-69%). 5-year CEA vs medical ipsilateral-stroke risk (15.7% vs 22.2%; ARR ~6.5%; RRR ~29%; NNT ~15) from WikiJournalClub NASCET summary (open-access, citing NEJM 1998); pooled 5-year RR ~0.84 for moderate stenosis from the Cochrane/CEA synthesis PMC6481587; CEA candidacy for >=50% symptomatic stenosis from StatPearls 'Carotid Endarterectomy' (NBK470582), Indications. | ✓ |
| 70-99% | Severe stenosis | Severe internal carotid artery stenosis by the NASCET method — a NASCET-derived diameter reduction of 70-99% (the residual lumen is reduced to little more than a thread relative to the normal distal ICA). This is the high-grade stenotic-but-still-patent band, short of complete occlusion. | Symptomatic 70-99% stenosis showed the greatest benefit from carotid endarterectomy in NASCET, establishing the 70% threshold as a key indication for surgery in symptomatic patients; the severe arm of the trial was stopped early because the benefit was so pronounced. | Highest stroke risk and greatest surgical benefit of the symptomatic bands. In the pooled trial analysis, CEA roughly halved the 5-year ipsilateral-stroke risk for severe (70-99%) stenosis (RR ~0.47, approximately 10% surgical vs 23% medical). The benefit was large enough that the severe arm was terminated early and all such patients referred for CEA. | Severity band from ESCR consensus (PMC9889495), 'Quantifying the degree of stenosis' ('severe' = 70-99%). Pooled 5-year ipsilateral-stroke RR ~0.47 (~10% surgical vs ~23% medical) for >=70% stenosis from the Cochrane/CEA synthesis PMC6481587; early termination of the severe arm and CEA benefit from WikiJournalClub NASCET summary (open-access) and StatPearls NBK470582, Indications. | ✓ |
| occlusion | Near occlusion or occlusion | Complete (100%) occlusion of the internal carotid artery — there is no residual lumen, so a NASCET percent-stenosis ratio cannot be meaningfully computed (NASCET treated near-occlusion/occlusion as a distinct category rather than calculating a percentage). Distinct from the patent 70-99% severe band. | Carotid endarterectomy is generally not indicated for a completely (chronically) occluded ICA, since there is no lumen to reopen; management is medical/best-medical therapy. The separate 'near-occlusion' subgroup (a tight stenosis with a collapsed/threadlike distal ICA) showed little or no clear benefit from surgery in the NASCET analyses and is also typically managed medically. | Near-occlusion paradoxically carried a relatively low subsequent stroke risk on medical therapy in NASCET (lower than the 70-99% severe band), which is part of why surgical benefit was not demonstrated for it; complete occlusion is not amenable to revascularization. | Occlusion (100%) / near-occlusion handled as a distinct category beyond the calculable bands per ESCR consensus (PMC9889495), Table 1 categories 'Near-occlusion'/'Occlusion'. No-benefit/low-risk of near-occlusion and non-revascularization of complete occlusion from NASCET near-occlusion analyses as summarized in StatPearls NBK470582 and the NASCET/CEA syntheses (PMC8536099); near-occlusion percent-not-calculated point corroborated by Wikipedia 'Carotid artery stenosis'. | ✓ |

### Citações por categoria
- **<50%**: North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade stenosis (NASCET) (1991) — https://doi.org/10.1056/NEJM199108153250701 · Severity band from ESCR consensus (PMC9889495), 'Quantifying the degree of stenosis': 'According to NASCET, luminal stenosis is classified as "mild" (0-49%), "moderate" (50-69%), and "severe" (70-99%).' NASCET formula/measurement points from same section and from Wikipedia 'Carotid artery stenosis' Diagnosis section. 'No significant benefit <50%' and 'surgery tended to be harmful in participants with less than 30% stenosis' (RR ~1.25) from the Cochrane/CEA synthesis PMC6481587/PMC8536099 and StatPearls 'Carotid Endarterectomy' (NBK470582), Indications section.
- **50-69%**: North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade stenosis (NASCET) (1991) — https://doi.org/10.1056/NEJM199108153250701 · Severity band from ESCR consensus (PMC9889495), 'Quantifying the degree of stenosis' ('moderate' = 50-69%). 5-year CEA vs medical ipsilateral-stroke risk (15.7% vs 22.2%; ARR ~6.5%; RRR ~29%; NNT ~15) from WikiJournalClub NASCET summary (open-access, citing NEJM 1998); pooled 5-year RR ~0.84 for moderate stenosis from the Cochrane/CEA synthesis PMC6481587; CEA candidacy for >=50% symptomatic stenosis from StatPearls 'Carotid Endarterectomy' (NBK470582), Indications.
- **70-99%**: North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade stenosis (NASCET) (1991) — https://doi.org/10.1056/NEJM199108153250701 · Severity band from ESCR consensus (PMC9889495), 'Quantifying the degree of stenosis' ('severe' = 70-99%). Pooled 5-year ipsilateral-stroke RR ~0.47 (~10% surgical vs ~23% medical) for >=70% stenosis from the Cochrane/CEA synthesis PMC6481587; early termination of the severe arm and CEA benefit from WikiJournalClub NASCET summary (open-access) and StatPearls NBK470582, Indications.
- **occlusion**: North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade stenosis (NASCET) (1991) — https://doi.org/10.1056/NEJM199108153250701 · Occlusion (100%) / near-occlusion handled as a distinct category beyond the calculable bands per ESCR consensus (PMC9889495), Table 1 categories 'Near-occlusion'/'Occlusion'. No-benefit/low-risk of near-occlusion and non-revascularization of complete occlusion from NASCET near-occlusion analyses as summarized in StatPearls NBK470582 and the NASCET/CEA syntheses (PMC8536099); near-occlusion percent-not-calculated point corroborated by Wikipedia 'Carotid artery stenosis'.


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> Conteúdo de referência reescrito. Confira a publicação primária vigente. Não é dispositivo médico nem substitui o julgamento clínico. O radiologista responsável pelo laudo permanece o autor e o responsável.

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