| AAA Size (cm) | Growth rate (cm/yr) | Annual rupture risk (%) |
|---|
| 3.0-3.9 | 0.39 | 0 |
| 4.0-4.9 | 0.36 | 0.5-5 |
| 5.0-5.9 | 0.43 | 3-15 |
| 6.0-6.9 | 0.64 | 10-20 |
| >=7.0 | - | 20-50 |
Although the current standard of determining rupture risk is based on maximum diameter, it is known that smaller AAAs that fall below this threshold (diameter<5.5 cm) may also rupture, and larger AAAs (diameter>5.5 cm) may remain stable. In one report, it was shown that 10 - 24% of ruptured AAAs were less than 5 cm in diameter.
Alternative methods of rupture assessment have been recently reported. The majority of these approaches involve the numerical analysis of AAAs using the common engineering technique of the finite element method (FEM) to determine the wall stress distributions. Recent reports have shown that these stress distributions have been shown to correlate to the overall geometry of the AAA rather than solely to the maximum diameter. It is also known that wall stress alone does not completely govern failure as an AAA will usually rupture when the wall stress exceeds the wall strength. In light of this, rupture assessment may be more accurate if both the patient-specific wall stress is coupled together with patient-specific wall strength. A non-invasive method of determining patient-dependent wall strength was recently reported, with more traditional approaches to strength determination via tensile testing performed by other researchers in the field. Some of the more recently proposed AAA rupture-risk assessment methods include: AAA wall stress; AAA expansion rate; degree of asymmetry; a rupture potential index (RPI); a finite element analysis rupture index (FEARI); biomechanical factors coupled with computer analysis; growth of ILT; geometrical parameters of the AAA; and also a method of determining AAA growth and rupture based on mathematical models.
Further Reading
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