A systematic review 1 including 9 studies with a total of 619 subjects was abstracted in DARE. The crude sensitivity ranged from 66 to 98%. The predicted change point in aneurysm size was 7.7 mm (95% confidence interval, CI: 7.0 to 8.9), above which false negatives did not occur. The sensitivities stratified by aneurysm size ranged from 53% (95% CI: 44 to 62) for 2-mm aneurysms to 95% (95% CI: 92 to 97) for 7-mm aneurysms. The crude specificity ranged from 77 to 100%. The overall estimated specificity for the studies was 98.9% (95% CI: 91.5 to 99.99), but there was between-study heterogeneity. The medium sensitivity for ruptured aneurysms, as derived from computer simulations, was 92% (95% CI: 90 to 94); the corresponding medium sensitivities for unruptured aneurysms and for aneurysms greater than 5 mm were 82% (95% CI: 78 to 86) and 92% (95% CI: 89 to 95), respectively. When screening for an unruptured aneurysm of at least 6 mm, with a low pre-test probability of 2%, a negative CTA resulted in a post-test probability of 0.024%. For a high pre-test probability of 10%, the post-test probability after a negative CTA was 0.13%. For a pre-test probability of 2% the post-test probability of a true-positive was 68%, and for a pre-test probability of 10%, the post-test probability was 92%. False-positives for aneurysms greater than 6 mm are unlikely.
Comment: The quality of evidence is downgraded by indirectness: The results may not be replicable in clinical practice. The authors conclude that CTA is useful in the descriptive imaging of a known aneurysm. Small aneurysms detected by CTA should be investigated further, unless there is a high pre-test probability of a ruptured aneurysm. When screening for ruptured aneurysms, a negative CTA should be investigated further. However, a negative CTA results in a very low probability of a clinically important aneurysm when screening for unruptured aneurysms.
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