Elsevier

Journal of Vascular Surgery

Volume 49, Issue 2, February 2009, Pages 443-454
Journal of Vascular Surgery

Basic research study
Vessel asymmetry as an additional diagnostic tool in the assessment of abdominal aortic aneurysms

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Objective

Abdominal aortic aneurysm (AAA) rupture is believed to occur when the local mechanical stress exceeds the local mechanical strength of the wall tissue. On the basis of this hypothesis, the knowledge of the stress acting on the wall of an unruptured aneurysm could be useful in determining the risk of rupture. The role of asymmetry has previously been identified in idealized AAA models and is now studied using realistic AAAs in the current work.

Methods

Fifteen patient-specific AAAs were studied to estimate the relationship between wall stress and geometrical parameters. Three-dimensional AAA models were reconstructed from computed tomography scan data. The stress distribution on the AAA wall was evaluated by the finite element method, and peak wall stress was compared with both diameter and centerline asymmetry. A simple method of determining asymmetry was adapted and developed. Statistical analyses were performed to determine potential significance of results.

Results

Mean von Mises peak wall stress ± standard deviation was 0.4505 ± 0.14 MPa (range, 0.3157-0.9048 MPa). Posterior wall stress increases with anterior centerline asymmetry. Peak stress increased by 48% and posterior wall stress by 38% when asymmetry was introduced into a realistic AAA model.

Conclusion

The relationship between posterior wall stress and AAA asymmetry showed that excessive bulging of one surface results in elevated wall stress on the opposite surface. Assessing the degree of bulging and asymmetry that is experienced in an individual AAA may be of benefit to surgeons in the decision-making process and may provide a useful adjunct to diameter as a surgical intervention guide.

Clinical Relevance

There is much debate about the most appropriate time to intervene with surgical treatment of abdominal aortic aneurysms. Currently, maximum diameter is deemed the most accurate indicator of rupture potential because size is not only an obvious factor in the decision-making process but is also easy for the clinician to determine from computed tomography scans. The method of determining vessel asymmetry proposed here is easy to interpret and was shown to be as significant as diameter in the cases examined. Therefore, asymmetry could become a useful adjunct to diameter in the decision-making process of the clinician.

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Supported by the Irish Research Council for Science, Engineering and Technology (IRCSET) Grant RS/2005/340, and Grant No. R01-HL-060670 from the United States National Heart Lung and Blood Institute.

Competition of interest: none.