European Journal of Vascular & Endovascular Surgery
Volume 31, Issue 3 , Pages 237-238, March 2006

The Small Abdominal Aortic Aneurysm

  • J. Golledge

      Affiliations

    • The Vascular Biology Unit, James Cook University, Townsville, Qld 4811, Australia
    • Corresponding Author InformationCorresponding author. Prof. Jonathan Golledge, Director, The Vascular Biology Unit, James Cook University, Townsville, Qld 4811, Australia.
    • ,
  • J. Muller

      Affiliations

    • The Vascular Biology Unit, James Cook University, Townsville, Qld 4811, Australia
    • ,
  • D. Coomans

      Affiliations

    • School of Mathematical and Physical Sciences, James Cook University, Townsville, Qld 4811, Australia
    • ,
  • P.J. Walker

      Affiliations

    • Department of Surgery, University of Queensland, Clinical Sciences Building, D Floor Room D6, Royal Brisbane and Women's Hospital, Herston, Qld 4029, Australia
    • ,
  • P.E. Norman

      Affiliations

    • School of Surgery and Pathology, University of Western Australia, Fremantle Hospital, Fremantle, WA 6959, Australia

Accepted 28 October 2005. published online 22 December 2005.

Article Outline

 

Despite a number of large randomised trials (with more underway) the management of small abdominal aortic aneurysms remains controversial.1, 2, 3 In this issue of the European journal of vascular and endovascular surgery Vega de Ceniga and colleagues report on the growth rate of abdominal aortic aneurysms measuring <5cm in maximum diameter followed for a mean of four and half years.4 The authors divide the patients into two groups with aortic diameters measuring 3–3.9cm (n=246) and 4–4.9cm (n=106) imaged by annual ultrasound and 6-monthly CT, respectively. The authors report that the larger aneurysms grow at over twice the rate of smaller aneurysms (4.7 compared to 2.1mm/year) and using Kaplan–Meier analysis estimated that 56 and 82% compared to 2 and 18% of aortas reached 5cm diameter by 2 and 5 years, respectively.4

The study of aortic aneurysm growth has important implications in a number of areas, including understanding the pathogenesis of the disease, as a basis for comparison with aortic diameters following endovascular aneurysm repair (EVAR) and in order to develop new treatment protocols. At present the treatment of small aneurysms is conservative in most centres with intervention reserved for those expanding to beyond a diameter limit of between 5 and 5.5cm. Evidence in support of this policy is provided by two large randomised trials which showed no advantage of early surgery for aortic aneurysms measuring a maximum diameter of 4–5.5cm, and demonstrated it was safe to follow an ultrasound surveillance approach with intervention primarily determined by growth to the intervention diameter.1, 2 Despite this evidence there is increasing interest in treating smaller aneurysm using EVAR, which is associated with lower early and medium term aneurysm-related mortality than open surgery.5, 6 Based on the findings of Vega de Ceniga et al., it could be argued that since the majority of 4–4.9cm aneurysms are going to reach 5cm within 2–5 years EVAR could reasonably by undertaken at aortic diameters under 5cm. Prior to accepting this approach a number of issues need to be considered, namely the calculation of aneurysm growth, the long-term outcome and cost of EVAR and the opportunity to develop medical treatments for aortic aneurysms.

The study of aneurysm progression using maximal diameter is hampered by the variable growth pattern of aneurysms, the loss of patients undergoing intervention or coming to the end of follow-up and the measurement error of the imaging modality.7, 8 The variation in aortic aneurysm growth patterns has received little attention. In a recent report of the UK Small Aneurysm Trial (UKSAT), Brady and colleagues reported a variety of growth patterns in patients followed-up for many years characterised by growth spurts and periods of stasis and in 6.4% aneurysm regression.7 Vega de Ceniga et al. noted no aneurysm growth in 25 and 18% of 3–3.9 and 4–4.9cm aneurysms, respectively.4 In calculating mean aneurysm expansion rates many authors use a statistical model in order to represent the behaviour of the cohort, such as linear regression, quadratic model or exponential growth. The variation in aneurysm growth is rarely taken into account with most authors using linear regression, which has been found to be less representative than a quadratic model.7 The random nature of growth and losses to follow-up due to intervention has been interpreted as requiring a Bayesian multilevel random effects model using quadratic regression terms.7 On the basis of this model, UKSAT clearly demonstrated that a simple linear regression approach over-estimates aneurysm growth rate by 29%.7 While Vega de Ceniga and colleagues did not outline their method of growth calculation it is assumed a linear expansion model was employed and may be one reason why they reported a greater percentage of aneurysms expanding to intervention level at 5 years than noted in the small aneurysm trials (around 60% at 5 years).1, 2

The recent EVAR 1 trial reported that aneurysm related mortality was slightly lower in patients undergoing EVAR compared to open aortic surgery, however, all cause mortality was equivalent and cost and complications greater with EVAR.6 The re-intervention rate was around 20% during the first 5 years following stent-graft insertion.6 Rather than interpreting the findings of studies such as those of Vega de Ceniga et al. as support for lowering the diameter threshold for EVAR, we feel that the results favour greater investigation of medical treatments for aortic aneurysm. For example, Vega de Ceniga et al. confirmed the intriguining observation that diabetes and occlusive lower limb artery disease are associated with reduced aneurysm expansion.4, 7 A number of suggestions have been made for the negative association of diabetes with aneurysm presence and growth, such as changes in extracellular matrix and proteolysis.9 These important negative associations along with the increased recognition of variable growth patterns provide an important basis for investigations of the mechanisms underlying aneurysm development and progression. The great interest in extending EVAR to smaller aneurysms would be benefited by an equally strong push to develop drug therapies.

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Acknowledgements 

JG and PN are supported by funding from the NHMRC (279408) and the NIH (R01 HL080010-01).

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References 

  1. The UK Small Aneurysm Trial Participants. Long-term outcomes of immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med. 2002;346:1445–1453
  2. Lederle FA, Wilson SE, Johnson GR, Reinke DB, Littooy FN, Archer CW, et al. Immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med. 2002;346:1437–1443
  3. Cao P, CAESAR Trial Collaborators . Comparison of surveillance vs endografting for small aneurysm repair (CAESAR) trial: study design and progress. Eur J Vasc Endovasc Surg. 2005;30:245–251
  4. Vega de Ceniga M, Gomez R, Estallo L, Rodriguez L, Banquer M, Barba A. Growth rate and associated factors in small abdominal aortic aneurysms. Eur J Vasc Endovasc Surg 2006; this issue (doi: 10.1016/j.ejvs.2005.10.007).
  5. Greenhalgh RM, Brown LC, Kwong GP, Powell JT, Thompson SG, EVAR trial participants . Comparison of endovascular aneurysm repair with open repair in patients with abdominal aortic aneurysm (EVAR trial 1), 30-day operative mortality results: randomised controlled trial. Lancet. 2004;364(9437):843–848
  6. EVAR trial participants. Endovascular aneurysm repair versus open repair in patients with abdominal aortic aneurysm (EVAR trial 1): randomised controlled trial. Lancet. 2005;365(9478):2179–2186
  7. Brady AR, Thompson SG, Fowkes GR, Greenhalgh RM, Powell JT. Abdominal aortic aneurysm expansion. Risk factors and time intervals for surveillance. Circulation. 2004;110:16–21
  8. Singh K, Jacobsen BK, Solberg S, Kumar S, Arnesen E. The difference between ultrasound and computer tomography measurements of aortic diameter increases with aortic diameter: analysis of axial images of abdominal aortic and common iliac artery diameter in normal and aneurismal aortas. Eur J Vasc Endovasc Surg. 2004;28:159–167
  9. Powell JT, Brady AR. Detection, management and prospects for the medical treatment of small abdominal aortic aneurysms. Arterioscler Thromb Vasc Biol. 2004;24:241–245

PII: S1078-5884(05)00701-X

doi:10.1016/j.ejvs.2005.10.032

European Journal of Vascular & Endovascular Surgery
Volume 31, Issue 3 , Pages 237-238, March 2006

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