Elsevier

Annals of Vascular Surgery

Volume 22, Issue 1, January–February 2008, Pages 37-44
Annals of Vascular Surgery

Clinical Research
Analysis of Expansion Patterns in 4-4.9 cm Abdominal Aortic Aneurysms

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Our objective was to analyze the growth pattern of 4-4.9 cm infrarenal abdominal aortic aneurysms (AAAs). We used an observational, longitudinal, prospective study design. We followed 4-4.9 cm AAAs with 6-monthly abdominal computed tomographic (CT) scans (January 1988-August 2004). AAA growth was defined as an increase in aortic diameter ≥2 mm in each surveillance period. We established the aortic expansion pattern in AAA with three or more CT scans as continuous, discontinuous. The latter includes at least one period of nongrowth (<2 mm/6 months). We studied the influence of cardiovascular risk factors (CVRFs), comorbidity, and AAA anatomical characteristics using the chi-squared test, t-test, life tables, and Kaplan-Meier for statistical analysis. We included 195 patients: 183 (93.8%) men, age 71 ± 8.3 years (50-90). The follow-up period was 50 ± 36.4 months (6.5-193.7). The growth pattern (n =131) was continuous in 15 (11.5%) and discontinuous in 116 (88.5%) AAA. The mean expansion rate was higher in AAAs with continuous expansion (7.92 ± 3.74 vs. 2.74 ± 2.94 mm/year, p < 0.0001). No CVRFs or comorbidity influenced the expansion pattern (p > 0.05). The eccentric thrombus was associated with a greater incidence of continuous growth (p = 0.05), with no influence of aortic calcification (p > 0.1). The expansion of 4-4.9 cm AAA is mostly irregular and unpredictable. We have not found any modifiable risk factors which influence their growth pattern. The eccentric distribution of the thrombus is associated with continuous expansion.

Introduction

The growth rates of small abdominal aortic aneurysms (AAAs) have been established as 3-6.9 mm/year.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 This is a practical way of evaluating AAA expansion and rupture risk, but it assumes a linear or at least a continuous and stable pattern of growth. However, AAAs have been reported to grow exponentially or even irregularly rather than linearly,4, 6, 8, 9, 10, 12, 13, 14 although there is only very limited evidence on this issue.

There is currently much debate on the best management for patients with small (<5 cm) AAAs. The UK Small Aneurysm Trial (UKSAT) and the Aneurysm Detection and Management Trial (ADAM) recommended conservative treatment due to very small rupture risk in 4-5.5 cm AAAs.15, 16 Two trials comparing surveillance versus endovascular aortic repair (EVAR) for small AAAs are currently being conducted (Comparison of Surveillance vs. Aortic Endografting for Small Aneurysm Repair [CAESAR] in Europe and PIVOTAL in the United States),17 and their results are expected by the end of 2007.

Besides defining AAA growth rates and possible influencing factors, in order to accurately learn about the natural history of AAAs, to help predict AAA enlargement, and to make precise surgical or endovascular indications, we believe it is important to study the pattern of growth of these small AAAs.

The objective of our study was to establish the growth pattern in our series of 4-4.9 cm AAAs. We also analyzed some clinical and anatomical factors which may have influenced these expansion patterns.

Section snippets

Patients and Methods

This is an observational, prospective study, run from January 1988 until August 2004. We followed 195 consecutive patients diagnosed with a 4-4.9 cm asymptomatic infrarenal AAA. We included in the study all patients with 4-4.9cm infrarenal AAAs who were followed for at least 6 months (two or more consecutive scans). Our exclusion criteria included <4 cm and ≥5 cm AAA, location of the AAA other than infrarenal (juxtarenal, suprarenal, thoracoabdominal aneurysms), follow-up fewer than two CT

Results

We followed a total of 195 4-4.9 cm AAAs in our center. The clinical characteristics of the series are reflected in Table I. The mean initial AAA size was 42.5 ± 2.8 mm (40-49). The mean follow-up period was 50 ± 36.4 months (6.5-193.7). During the follow-up, 49 patients (25.1%) died, one (0.5%) after AAA elective repair and two (1%) because of AAA rupture. One additional AAA ruptured during the follow-up at size 5.6 cm in a patient who was considered unfit for elective surgery due to severe

Discussion

The growth rate of AAA is usually reported using the ratio of the difference between the final and the initial CT AAA diameters and the time interval in between (mm/year). However, this rate does not really express the natural history of the AAA, and it does not precisely predict the sequential changes in AAA size. Hirose et al.13 expressed the AAA growth curve as a monoexponential equation for electively repaired AAAs and a biexponential equation for AAAs which eventually ruptured. The former

Conclusions

The expansion of 4-4.9 cm AAAs is mostly irregular and unpredictable. A 6-month period of expansion does not necessarily imply additional continuous rapid growth. The expansion rates may differ greatly between one observational period and the next, but eventually almost half of them will reach a surgical size after 2 years and 70% after 5 years. The patients can be evaluated and prepared for elective AAA repair, but hasty surgical decisions cannot be made on the asumption that <5 cm AAAs expand

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