Understanding "No Hemodynamically Significant Internal Carotid Artery Stenosis"
"No hemodynamically significant internal carotid artery stenosis" means there is less than 70% narrowing of the internal carotid artery, and therefore the stenosis is not severe enough to cause reduced blood flow to the brain that would impact cerebral perfusion.
Definition and Measurement
Hemodynamically significant internal carotid artery (ICA) stenosis generally refers to a narrowing of 70% or greater, which is the threshold at which blood flow becomes significantly compromised 1.
Carotid stenosis is typically measured using duplex ultrasonography, which combines 2-dimensional real-time imaging with Doppler flow analysis to evaluate blood flow velocity as an indicator of stenosis severity 1.
According to established guidelines, specific velocity criteria are used to classify the degree of stenosis 1:
- Peak systolic velocity (PSV) <110 cm/s: 0-29% stenosis
- PSV 111-130 cm/s: 30-49% stenosis
- PSV >130 cm/s, end-diastolic velocity (EDV) <100 cm/s: 50-69% stenosis
- PSV >130 cm/s, EDV >100 cm/s: 70-99% stenosis (hemodynamically significant)
Clinical Significance
A finding of "no hemodynamically significant stenosis" indicates that the patient has either no stenosis or a stenosis less than 70% that is unlikely to cause cerebral hypoperfusion 1.
Patients with non-hemodynamically significant stenosis (less than 70%) have a lower risk of stroke compared to those with stenosis of 70% or greater 2, 3.
Even non-hemodynamically significant stenosis may still represent atherosclerotic disease and could be a marker for systemic atherosclerosis and risk for coronary events 1.
Hemodynamic Impact
In carotid stenosis less than 70%, blood flow is typically maintained at adequate levels through the stenotic segment without significant pressure drop across the lesion 4, 5.
The primary mechanism of stroke in patients with carotid stenosis is typically embolization rather than hemodynamic compromise in those with non-hemodynamically significant stenosis 4.
Collateral circulation plays a crucial role in maintaining cerebral perfusion, which is why some patients with even severe stenosis may remain asymptomatic 6, 5.
Management Implications
For asymptomatic patients with non-hemodynamically significant carotid stenosis (<70%), medical therapy remains the mainstay of treatment 3.
Invasive treatments like carotid endarterectomy or stenting are generally not indicated for asymptomatic patients with stenosis less than 70% 1, 3.
For symptomatic patients (those who have had TIA or stroke), even moderate stenosis (50-69%) may warrant consideration for intervention, though severe stenosis (70-99%) carries the strongest indication 3.
Monitoring Recommendations
For patients with non-hemodynamically significant stenosis (50-69%), it is reasonable to perform annual duplex ultrasonography to monitor for progression 1.
Once stability has been established over an extended period, longer intervals between surveillance imaging may be appropriate 1.
If the stenosis progresses to become hemodynamically significant (≥70%), reassessment of management strategy would be warranted 1.
Conclusion
When a report indicates "no hemodynamically significant internal carotid artery stenosis," it means the patient has a stenosis less than 70%, which is unlikely to cause cerebral hypoperfusion but may still represent atherosclerotic disease requiring medical management and surveillance.