Non-invasive imaging of carotid artery stenosis

Background and Purpose:

Carotid endarterectomy has been shown to be beneficial in symptomatic patients with a severe stenosis (70-99%) of the internal carotid artery (ICA). Digital subtraction angiography (DSA) is the standard of reference in the diagnosis of carotid artery stenosis, but has a relatively high complication rate. In this thesis in a diagnostic study and a cost-effectiveness analysis we investigated whether DSA could be replaced by non-invasive testing.

Methods:
In a prospective diagnostic study we performed duplex ultrasound (DUS), magnetic resonance angiography (MRA), and DSA on 350 consecutive symptomatic patients. Stenoses were measured with the observers blinded for clinical information and other test results. Separate and combined test results of DUS and MRA were compared with DSA. Only the stenosis measurements of the arteries on the symptomatic side were included in the analyses. A cost-effectiveness analysis, integrating diagnostic accuracy, acute complications, long term outcomes, costs and quality of life was performed by means of a diagnostic and prognostic model. Additionally, in this thesis further test specific characteristics of MRA were studied and patients preferences for DSA, MRA, and DUS were investigated.

Results:
DUS analysed with previously defined criteria resulted in a sensitivity of 87.5% (95%CI, 82.1%-92.9%) and a specificity of 75.7% (95%CI, 69.3%-82.2%) in identifying severe ICA stenosis (70-99%). Stenosis measurements on MRA yielded a sensitivity of 92.2% (95%CI, 86.2%-96.2%) and a specificity of 75.7% (95%CI, 68.6%-82.5%). Combining MRA and DUS results, agreement between these two modalities (84% of patients) gave a sensitivity of 96.3% (95%CI, 90.8%-99.0%) and a specificity of 80.2% (95%CI, 73.1%-87.3%) for identifying severe stenosis. The use of DUS, MRA, and the combination of DUS and MRA resulted in comparable outcomes in terms of QALYs and total lifetime costs, whereas DSA resulted in QALY loss and higher costs.

Conclusions:
Both DUS and MRA are accurate diagnostic tests to detect carotid artery stenosis. Particularly if DUS and MRA are in agreement, the combined test result has a high sensitivity and specificity, making DSA redundant for the decision whether carotid endarterectomy should be performed. In the event of disagreement DSA may be considered. In the majority of patients it is more effective and less expensive to replace DSA by the combination of DUS and MRA.