Editors' commentary

Abstract

The abdominal aortic aneurysm (AAA) diameter is a key component in the surveillance of AAAs for the assessment of aneurysm progression. AAA external diameter has been shown to be a reliable method for repeated measurements in cases near the threshold for surgical referral. Other measures such as volume or wall stress have had, until now, a limited value in clinical practice. This argument was well developed by Mastracci et al in this debate. But with reported mean annual growth rates of 2 to 3 mm in diameter, a high reproducibility is required to allow detection of small changes in AAA diameter. In a systematic review of ultrasound measurement of the abdominal aorta diameter, Beales et al1Beales L. Wostenhulme S. Evans J.A. West R. Scott D.J.A. Reproducibility of ultrasound measurement of the abdominal aorta.Br J Surg. 2011; 98: 1517-1525Crossref PubMed Scopus (87) Google Scholar reported intraobserver and interobserver values greater than the 5-mm level regarded as acceptable by the U.K. and U.S. screening programs. These differences may have had a significant clinical impact on screening and surveillance. In addition, even though ultrasound diameter imaging has been used for years, no standardized image acquisition exists. This limitation has been emphasized by Bredahl et al,2Bredahl K. Eldrup N. Meyer C. Eiberg J.E. Sillesen H. Reproducibility of ECG-gated ultrasound diameter assessment of small abdominal aortic aneurysms.Eur J Vasc Endovasc Surg. 2013; 45: 235-240Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar who showed the importance of a standardized protocol including electrocardiograph-gating and subsequent off-line reading with minute caliper placement to reduce variability. Grondal et al have also shown that measurement of the maximum external AAA diameter by ultrasound is influenced by the pulse wave propagation, with an average difference of 1.9 mm between diastole and systole and a wide range in variation (0-4.7 mm).3Grondal N. Bramsen M.B. Thomsen M.D. Rasmussen C.B. Lindholt J.S. The cardiac cycle is a major contributor to variability in size measurements of abdominal aortic aneurysms by ultrasound.Eur J Vasc Endovasc Surg. 2012; 43: 30-33Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar This explains why ultrasound has been supplanted by computed tomography angiography with the use of center-lumen of flow by postprocessing software to estimate the AAA diameter with greater accuracy. As discussed by our debaters, assessment of the AAA volume is another parameter beyond diameter. It allows measurement of contour changes of the AAA and intraluminal thrombus volume. Using segmentation software, it permits accurate measurements of the AAA volume even using non-contrast-enhanced computed tomography scans. Volumetric measurements also have a higher sensitivity for AAA growth than diameter measurements. In addition, three-dimensional ultrasound permits quantification of the intraluminal thrombus without any risk of contrast agent or radiation. As shown by van Keulen,4van Keulen J.W. van Prehn J. Prokop M. Moll F.L. van Herwaarden J.A. Potential value of aneurysm sac volume measurements in addition to diameter measurements after endovascular aneurysm repair.J Endovasc Ther. 2009; 16: 506-513Crossref PubMed Scopus (47) Google Scholar aortic volume measurement may be particularly useful for surveillance after endovascular aneurysm repair. In his study, sac expansion was detected by volumetry in 32 patients, although an increase in sac diameter was seen only in 14 of them. Despite ample evidence,5Prinssen M. Verhoeven E.L. Verhagen H.J. Blankensteijn J.D. Decision-making in follow-up after endovascular aneurysm repair based on diameter and volume measurements: a blinded comparison.Eur J Vasc Endovasc Surg. 2003; 26: 184-187Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar, 6Wever J.J. Blankensteijn J.D. Th M Mali W.P. Eikelboom B.C. Maximal aneurysm diameter follow-up is inadequate after endovascular abdominal aortic aneurysm repair.Eur J Vasc Endovasc Surg. 2000; 20: 177-182Abstract Full Text PDF PubMed Scopus (151) Google Scholar volume assessment is still not carried out in many institutions. The reasons are many: Volume assessment is time consuming and requires dedicated software and skilled technicians and may be difficult to organize in high-volume centers. Furthermore, observer variability still exists in multiplanar reconstructions. Finally, the ability of aortic volume to predict rupture has not been established.7Parr A. Jayaratne C. Buttner P. Golledge J. Comparison of volume and diameter measurement in assessing small abdominal aortic aneurysm expansion examined using computed tomographic angiography.Eur J Radiol. 2011; 79: 42-47Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar In conclusion, even if volumetric measurements are likely to be of value in assessing the efficacy of new therapies for small AAA, we need more evidence to revise our guidelines, based until now on diameter thresholds. The role of diameter versus volume as the best prognostic measurement of abdominal aortic aneurysmsJournal of Vascular SurgeryVol. 58Issue 1PreviewAccurate measurement of abdominal aortic aneurysms is necessary to predict rupture risk and, more recently, to follow aneurysm sac behavior following endovascular repair. Up until this point, aneurysm diameter has been the most common measurement utilized for these purposes. Although aneurysm diameter is predictive of rupture, accurate measurement is hindered by such factors as aortic tortuosity and interobserver variability, and it does not account for variations in morphology such as saccular aneurysms. Full-Text PDF Open Archive