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Multidimensional growth measurements ofabdominal aortic aneurysmsGiampaolo Martufi, PhD,a Martin Auer, PhD,b Joy Roy, MD, PhD,c Jesper Swedenborg, MD, PhD,c

Natzi Sakalihasan, MD, PhD,d Giuseppe Panuccio, MD,e,f and T. Christian Gasser, PhD,a Stockholm, Sweden;Vienna, Austria; Liège, Belgium; Perugia, Italy; and Münster, Germany

Background: Monitoring the expansion of abdominal aortic aneurysms (AAAs) is critical to avoid aneurysm rupture insurveillance programs, for instance. However, measuring the change of the maximum diameter over time can only providelimited information about AAA expansion. Specifically, regions of fast diameter growth may be missed, axial growthcannot be quantified, and shape changes of potential interest for decisions related to endovascular aneurysm repair cannotbe captured.Methods: This study used multiple centerline-based diameter measurements between the renal arteries and the aorticbifurcation to quantify AAA growth in 51 patients from computed tomography angiography (CTA) data. Criteria forinclusion were at least 1 year of patient follow-up and the availability of at least two sufficiently high-resolution CTAscans that allowed an accurate three-dimensional reconstruction. Consequently, 124 CTA scans were systematicallyanalyzed by using A4clinics diagnostic software (VASCOPS GmbH, Graz, Austria), and aneurysm growth was monitoredat 100 cross-sections perpendicular to the centerline.Results: Monitoring diameter development over the entire aneurysm revealed the sites of the fastest diameter growth,quantified the axial growth, and showed the evolution of the neck morphology over time. Monitoring the development ofan aneurysm’s maximum diameter or its volume over time can assess the mean diameter growth (r [ 0.69, r [ 0.77) butnot the maximum diameter growth (r [ 0.43, r [ 0.34). The diameter growth measured at the site of maximumexpansion was w16%/y, almost four times larger than the mean diameter expansion of 4.4%/y. The sites at which themaximum diameter growth was recorded did not coincide with the position of the maximum baseline diameter (r [ 0.12; P [ .31). The overall aneurysm sac length increased from 84 to 89 mm during the follow-up (P < .001), whichrelates to the median longitudinal growth of 3.5%/y. The neck length shortened, on average, by 6.2% per year and wasaccompanied by a slight increase in neck angulation.Conclusions: Neither maximum diameter nor volume measurements over time are able to measure the fastest diametergrowth of the aneurysm sac. Consequently, expansion-related wall weakening might be inappropriately reflected by thistype of surveillance data. In contrast, localized spots of fast diameter growth can be detected through multiple centerline-based diameter measurements over the entire aneurysm sac. This information might further reinforce the quality ofaneurysm surveillance programs. (J Vasc Surg 2013;-:1-8.)

Clinical Relevance: Although the size of the aneurysm still remains the most accepted predictor of rupture risk, smallabdominal aortic aneurysms (AAAs) may also rupture. Thus, the new tools presented in this study use three-dimensionalaneurysm models, based on computed tomography angiography and multiple centerline-based diameter measurementsover the entire aneurysm sac, could help clinicians when making decisions to treat AAAs and when choosing alternativetreatments for AAAs, regardless of the diameter size.

The indication for elective abdominal aortic aneurysm rupture and is given for aneurysms that reach a maximum

(AAA) repair is strongly related to the aneurysm’s risk for

the Department of Solid Mechanics, School of Engineering Sciences,oyal Institute of Technology (KTH), Stockholma; Vascops GmbH,evelopment, Viennab; the Department of Vascular Surgery, Karolinskaniversity Hospital and Institute, Stockholmc; the Department ofascular Surgery, University Hospital of Liege, Lièged; the Division ofascular and Endovascular Surgery, University of Perugia, Perugiae;d the Clinic for Vascular and Endovascular Surgery, Münster Univer-y Hospital, Münster.f

or conflict of interest: none.rint requests: Dr Giampaolo Martufi, Royal Institute of TechnologyTH), Department of Solid Mechanics, School of Engineering Sciences,eknikringen 8, 100 44 Stockholm. Sweden (e-mail: martufi@kth.se ortp://130.237.24.173/vascumech/index.html).editors and reviewers of this article have no relevant financial relationshipsdisclose per the JVS policy that requires reviewers to decline review of anyanuscript for which they may have a conflict of interest.-5214/$36.00yright � 2013 by the Society for Vascular Surgery.://dx.doi.org/10.1016/j.jvs.2012.11.070

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centerline-based diameter of 55 mm.1 However, severalreports have demonstrated a rupture risk of AAAs sized <5cm in diameter and also that the rate of expansion of theaneurysm is crucial for a certain number of AAAs, indepen-dent of their size.2-4 Therefore, a single threshold diameteris not appropriate for every patient, and the decision toperform elective AAA repair should ideally be individualized.Consequently, apart from aneurysm size, many other riskfactors for aneurysm rupture have been suggested. Forexample, aneurysm shape, blood pressure, female gender,and other wall-weakening effects have been mentionedspecifically.5

Apart from static criteria (ie, risk factors evaluated atone time point), dynamic risk factors, such as the expansionrate, have also been suggested.2-4 Aneurysm expansion incommon clinical practice is defined as the change inmaximum aortic diameter over time, and an expansionrate of 10 mm/y is generally considered as an indication

1

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Table I. Patient demographics and abdominal aorticaneurysm (AAA) details

Variable No. or mean (range)

Patients 51Age, years 70 (49-85)SexMale 44Female 7

Mean arterial pressure, mm Hg 97 (90-146)Surveillance time frame, months 12 (2-24)AAA diameter, mmBaseline 46.6 (34.7-56.4)Follow-up 49.5 (37-63)

JOURNAL OF VASCULAR SURGERY2 Martufi et al --- 2013

for elective repair.1,6 This practice is justified to someextent through an expected wall weakening effect inresponse to undesirable wall remodeling at fast AAAgrowth. Specifically, aneurysm expansion correlates withthe density of the inflammatory cell,7,8 which in turnincreases matrix metalloproteinase activity7,8 and leads tocompromised wall strength.9,10 This biologic activity islocalized, such that spots of increased expression and acti-vation of matrix metalloproteinases might contribute tofast local aneurysm expansion.7,8

The biomechanical rupture risk assessment alreadyintegrates many static risk factors into indices, such as thepeak wall stress11 and the peak wall rupture risk.12-14 Simi-larly, dynamic wall-weakening effect could potentially beintegrated, which might further improve the biomechanicalrupture risk assessment.

Developing models that prescribe aneurysm wall weak-ening as a consequence of their expansion rate requiresdetailed growth information. Available data are currentlybased on measuring the maximum diameter at two pointsin time, which clearly cannot provide a comprehensivepicture on how aneurysm size and shape change overtime. For example, the morphology of the aneurysm neckis especially important to minimize complications relatedto endovascular aneurysm repair (EVAR),15,16 and itschange over time can clearly not be studied from maximumdiameter measurements.

Measuring the expansion of AAAs also presents anumber of methodologic challenges. First, the change indiameter over time is small, nonlinear, and hard topredict.17 It is characterized by periods of rapid growth,followed by quiescience.18,19 Aortic diameter measure-ments that use ultrasound imaging and, to a lesser extent,computed tomography angiography (CTA), have a marginof error of 2 to 3 mm,17,20,21 which is within the range ofthe annual expansion of many small AAAs. Finally, thedevelopment of treatment protocols based on AAA expan-sion is somewhat limited due to missing follow-up data foraneurysms that reach the AAA repair indication threshold.

Measuring the maximum diameter at two points intime provides only limited information about aneurysmgrowth. Specifically, regions of fast diameter growth mightbe missed, axial growth cannot be quantified, and shapechanges of potential interest for EVAR-related decisionscannot be captured. Motivated by these limitations, theprincipal aim of the present study was to explore and inves-tigate the growth pattern of the entire AAA sac. A multidi-mensional analysis of AAA growth was applied to CTAfollow-up data from 51 patients. The applied analysismethod used multiple centerline-based diameter measure-ments between the renal arteries and the aortic bifurcation.Sites with the highest diameter growth and axial growth, aswell as the evolution of the neck morphology over time,could be extracted from the collected measurements.Finally, the derived growth information allowed a criticalevaluation of conventional procedures to measure AAAgrowth.

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METHODS

Cohort. Data for 51 patients with nonrupturedinfrarenal AAAs were retrospectively collected from theS. M. Misericordia Hospital Perugia, Italy (n ¼ 32), Karo-linska University Hospital, Stockholm, Sweden (n¼13),and University Hospital Liege, Belgium (n ¼ 6). Patientswere monitored between 2 and 24 months with repeatedcontrast-enhanced multislice CTA, where the medianoverall follow-up period was 12 months (interquartilerange [IQR], 11 to 13 months). Some further patient dataare given in Table I.

Criteria for inclusion were at least 1 year of patientfollow-up and the availability of at least two sufficientlyhigh-resolutionCTAscans that allowed accurate reconstruc-tion at two different time points. CTA scans with stronglyinhomogeneous lumen intensity were rejected. Other exclu-sion criteria were patients with chronic kidney disease,contrast agent intolerance, and symptomatic patients.

Patient age, sex, blood pressure, and smoking statuswere taken from patient records. The collection and useof anonymized data from human subjects was approvedby the local ethics committees.

Aneurysm geometry representation. Aortic geome-tries between the renal arteries and the aortic bifurcationfrom 124 CTA scans were systematically analyzed by a singleobserver. The three-dimensional (3D) AAA geometry(Fig 1, A) was reconstructed using deformable (active)contour models22 that were implemented in the A4clinics4.0 diagnostic software (VASCOPS GmbH, Graz, Austria).The accuracy of this type of geometric reconstruction is inthe range of one in-plane pixel size.22 All reconstructionswere verified by another author of the study.

Reconstructed AAA geometry was used to automati-cally calculate the aneurysm volume (V); that is, the volumethat is enclosed by the outer surface and between the trans-versal planes at the lowest renal artery and the aortic bifur-cation, respectively. Then, the 3D model was automaticallysliced orthogonally to the centerline so that the aneurysm’sluminal and outer surfaces were represented throughsplines (Fig 1, B). Specifically, 100 splines were used foreach aneurysm, which together with the centerline,

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Fig 1. Abdominal aortic aneurysm (AAA) geometry acquisition. A, Three-dimensional anatomy is reconstructed fromcomputed tomography angiography scans using a deformable segmentation model. B, Simplified geometry repre-sentation uses splines perpendicular to the aneurysm’s centerline.

Fig 2. Definition of the geometric properties of an abdominal aortic aneurysm (AAA). A, Centerline-based outeraortic diameters. Dmax, maximum diameter; D1, aortic diameter at the lowest renal artery. B, Centerline lengthsegments. N, neck length; S, aneurysm sac length. C, Angulation a.

print&web4C/FPO

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provided a simplified 3D representation. This geometricrepresentation allowed a fully automatic analysis witha specially developed in-house algorithm using MatLabsoftware (The MathWorks, Natick, Mass).

Luminal and outer diameters were measured from eachspline, which in turn defined the largest outer diameter(Dmax) and the diameter (D1) at the lowest renal artery(Fig 2, A). The aneurysm neck length (N), the portionbetween the lowest renal artery and the proximal onset ofthe aneurysmatic enlargement (ie, where the outer diameterwas 10% larger than the aortic diameter at the lowest renal

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artery [D1])23,24 was extracted (Fig 2, B). Similarly

extracted was the aneurysm sac length (S), the length ofthe centerline from the proximal onset of the aneurysmdown to the aortic bifurcation (Fig 2, B). Finally, the angu-lation (a) was computed (Fig 2,C); that is, the rotation thatis required, such that the extrapolation of the straightcenterline in the neck meets the aortic bifurcation.23,24

Aneurysm growth measurements. To quantify aneu-rysm growth, the changes of the geometric properties werecompared between two consecutive CTA scans. Multiplecomparisons were made for patients who had more than

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Fig 3. Box and whisker plots show multiple centerline-basedaneurysm expansions and global-based aneurysm expansions.gMAX, maximum diameter growth; gMEAN, mean diameter growth,which is averaged between the renal arteries and the aortic bifur-cation; gD, global maximum diameter-based expansion rate; gS,global longitudinal aneurysm expansion; gV, global volume-basedaneurysm expansion. The horizontal line in the middle of each boxindicates the median, the top and bottom borders of the box markthe 75th and 25th percentiles, respectively, the top whiskers markthe 75th percentile þ1.5 interquartile range (IQR), while thebottom whiskers mark the 25th percentile �1.5 IQR, and the þsymbols denote outliers.

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two CTA scans, and 7300 expansion observations wereprocessed in the present study.

Specifically, the nonlinear growth model

g ¼�X 1-year follow�up

X baseline � 1�$100

¼ ½Expð12 rÞ � 1�$100½%=y�;

where X baseline and X 1-year follow-up denote baseline and1-year follow-up quantities, was used. Exp (d) is theexponential function of (d). Because the measured quantityX was not always given at the 1-year follow-up, the loga-

rithmic growth factor r ¼ 1tLn

�X follow�up

X baseline

�was used to

calculate g, where t denotes the time interval betweentwo measurement points in months. Ln (d) is the naturallogarithmic function of (d).

To study the diameter expansion, g was computed at100 cross-sections along the aneurysm. Specifically, thediameters that were at the same relative centerline position,between the two time points at which CTA scans weretaken, were thought to correspond to each other. Fromthese measurements, maximum gMAX and mean gMEAN

diameter expansions were extracted.Standard maximum-diameter measures were used to

define the global maximum diameter-based expansion

rate gD, with r ¼ 1tLn

Dfollow�upmax

Dbaselinemax

which compares the

maximum diameters at baseline and follow-up. Note thatthe maximum diameters Dbaseline

max and Dfollow�upmax are, in

general, not at the same relative centerline position.Finally, volume measurements were used to define

global volume-based aneurysm expansion gV with

r ¼ 1tLn

�V follow�up

V baseline

�; and centerline length measurements

defined global longitudinal aneurysm expansion gS with

r ¼ 1tLn

�S follow�up

Sbaseline

�.

Statistics. Statistical analysis was performed withSPSS 20.0 software (SPSS Inc, Chicago, Ill). The nor-mality of the data was assessed using the Shapiro-Wilktest. The paired t-test was used for paired variables withnormal distribution, and the Wilcoxon matched pairs testwas used for non-normal data. For the null hypothesistest, a two-sided P < .05 was set to determine statisticalsignificance.

Correlations between the maximum diameter-basedexpansion rates ðgDÞ, the volume-based expansion ratesðgVÞ, and the multiple centerline-based growth measuresof gMAX and gMEAN were assessed. This analysis aimed atquantifying the extent to which aneurysm growth couldbe extracted from measuring the maximum diameters orthe volumes at two time points. In addition, the correlationbetween the site of the maximum diameter and the site ofmaximum growth was investigated.

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RESULTS

AAA growth measurements. The calculated growthmeasurements are shown in Fig 3. The maximum di-ameter growth gMAX (median, 16%/y; IQR, 12.3% to23%/y) was about four times larger than the mean diam-eter growth gMEAN (median, 4.4%/y; IQR, 2% to 7.4%/y).The maximum diameter growth gMAX differed significantly(P < .001) from gD(median, 6.4%/y; IQR, 3.5% to 8.6%/y) and gV(median, 10.7%/y; IQR, 7.7% to 17%/y); that is,the growth based on relating the maximum diameters orthe volumes measured at the two time points, respectively.

The overall aneurysm sac length (S) increased (P <.001) from 85.37 mm (IQR, 74.3 to 95.7 mm) to 89.44mm (IQR, 81.55 to 101.75 mm) during the follow-up,which relates to a median longitudinal growth ðgSÞ of3.5%/y (IQR, �0.84% to 11.5%).

The subgroup analysis reported in Table II found thatAAA expansion was not associated with age and mean arte-rial pressure but were increased in current smokers,women, and larger baseline diameters, similar to previousreports.17,25 However, none of the subgroup results re-ported in Table II reached statistical significance, probablydue to the small sample size.

The relative centerline position, at which the maximumdiameter growth gMAX was recorded, did not coincide withthe position of the maximum baseline diameter Dbaseline

max .This was confirmed by a Spearman coefficient of 0.12(P ¼ .31) that defined the correlation between the twofrequency distributions shown in Fig 4.

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Fig 4. Locations of maximum diameter growth ðgMAXÞ andmaximum baseline diameter ðDbaseline

max Þ as a function of the relativecenterline position. 0 corresponds with the renal arteries locationand 1 with the aortic bifurcation position.

Table II. Measured abdominal aortic aneurysm (AAA)growth by patient characteristics at baseline and riskfactors

Factor Pts, No.

AAA growth measurements, %per year (median)

gMAX gMEAN gD gV gS

Age at baseline,years (tertiles)

49-69 20 16.7 5 6.1 12.9 4.370-74 17 22.4 5.8 7.8 11.7 3.2475-85 14 16.8 4 5.2 10.7 3.79

SexMale 44 16.4 4.6 5.6 11.8 2.8Female 7 20.9 5.2 7.9 16.9 10.2

Dbaselinemax , mm (tertiles)35-45 17 15.7 3.2 4 10.3 2.4546-48 17 18.3 4.7 7 10.4 3.4448-56 17 18.9 5.9 7.2 16.7 5.9

Smoking statusNever 20 17.2 3.9 4.9 10.6 1.33Former 9 17.5 4.8 6.1 12.7 1.97Current 11 22.9 5.6 6.7 16.7 4.7Unknown 11 16.4 4.2 7 13.8 1.53

MAP at baseline,mm Hg (tertiles)

90-93 30 16.6 4.7 6.4 11.2 494-98 4 18.4 5.3 4.9 14.6 399-147 17 18.7 4.7 7.5 14 3.45

Dbaselinemax , Maximum diameter at baseline; gMAX , maximum diameter growth;

gMEAN , mean diameter growth; gD, global maximum diameter-basedexpansion rate; gS, global longitudinal aneurysm expansion; gV , globalvolume-based aneurysm expansion; MAP, mean arterial pressure.

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Correlation analysis. The correlations between themaximum diameter-based expansion rates gD, thevolume-based expansion rates gV, and the multiplecenterline-based growth measures gMAX and gMEAN areshown in Fig 5. These variables were distributed normally,and the Pearson correlation was calculated. Specifically,poor correlation was found between gMAX and gD(r ¼0.43; P < .001) as well as between gMAX and gV(r ¼ 0.34;P < .001), and gMAX and gMEAN (r ¼ 0.42; P < .001),which means that measuring the maximum diameters orthe volumes at two time points cannot be used to quantifythe maximum diameter growth.

In contrast, a correlation was seen between gMEAN

and gD (r ¼ 0.69; P < .001) as well as between gMEAN

and gV (r ¼ 0.77; P < .001), indicating that measuringthe maximum diameters or the volumes at two timepoints allows an estimation of the mean diameter growth.Moreover, no correlation was found between gMAX andgS (r ¼ 0.13; P ¼ .26) or between gMEAN and gS

(r ¼ �0.06; P ¼ .64).Aortic aneurysm neck evolution. There were no

significance differences (P ¼ .99) between the diametersD1 at the lowest renal artery at baseline (median, 23.93mm; IQR, 21.74 to 27.37 mm) and at follow-up(median, 24.16 mm; IQR, 22.02 to 27.02 mm). Themean diameter growth of 2.4%/y (IQR, �3.7% to 6.8%/y)

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and the maximum diameter growth of 6.9%/y (IQR, 0% to13%/y) defined the enlargement of the neck.

The aortic neck length N shrank slightly over time,from 17.53 mm (IQR, 11.00 to 29.12 mm) at baselineto 15.38 mm (IQR, 9.41 to 26.73 mm) at follow-up,which statistically was not a significant difference (P ¼.12). It corresponds to a median longitudinal growthof �6.2%/y (IQR, �33% to 22.3%/y; Fig 6).

A slight increase in aortic neck angulations a wasobserved, from 28.62� (IQR, 20.10� to 39.98�) at baselineto 29.48� (IQR, 20.78� to 43.54�) at follow-up, which wasnot statistically significant (P ¼ .32). It corresponds toamedian rate of 2.134�/y (IQR,�2.65� to 7.30�/y; Fig 6).

DISCUSSION

Fast growth of the aneurysm wall compromises itsstructural integrity,7-10 which naturally increases the riskfor AAA rupture. Consequently, monitoring the growth

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Fig 5. Association of maximum ðgMAXÞ and mean (gMEAN) diameter growth with global maximum diameter-basedexpansion rate ðgDÞ and global volume-based aneurysm expansion ðgVÞ with Pearson correlation.

Fig 6. Box and whisker plots of aortic aneurysm neck morphologychange during the follow-up period. The horizontal line in themiddle of each box indicates the median, the top and bottomborders of the box mark the 75th and 25th percentiles, respectively,the top whiskers mark the 75th percentile þ1.5 interquartile range(IQR), while the bottom whiskers mark the 25th percentile �1.5IQR, and the þ symbols denote outliers.

JOURNAL OF VASCULAR SURGERY6 Martufi et al --- 2013

of small AAAs is critical to avoid rupture in surveillanceprograms, for instance. AAA growth is currently monitoredby measuring the development of its maximum diameterover time. The present study showed that aneurysms didnot grow fastest at the site of the maximum diameter butrandomly anywhere along the aneurysmatic sac. Thus,monitoring the development of the maximum diameter isnot able to measure the maximum diameter growth of

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the aneurysm. Similarly, monitoring the volume of anAAA cannot predict its maximum growth. Althoughvolume measurements account to some extent for longitu-dinal growth, small focal areas of fast growth cannot bedistinguished from larger areas of slow growth.

In contrast, monitoring the development of themaximum diameter or the volume over time providesadequate measurements for the aneurysm’s average growthrate. Here, volume measurements are slightly better thanmaximum diameter measurements, indicating that volumemight be a more representative parameter to reflectmorphologic aneurysm changes, as suggested earlier.26

However, the complex shape of aneurysms is defined bystrong local changes in surface curvature,27 which naturallycannot be described by single parameters such as themaximum diameter or the volume.

The maximum diameter growth of about 16%/y in ourcohort was almost four times larger than the mean diam-eter expansion of 4.4%/y. Apart from diameter growth,the aneurysms also grew considerably in the longitudinaldirection by 3.5%/y. This observation questions moni-toring methods that are related to certain cross-sections.Because the aneurysm neck length shrank only minimallyover time (1.09 mm/y), the measured longitudinal growthtranslates into (further) bending of the aneurysm.

The observed absolute mean diameter growth over 1year of 2.05 mm/y is within the margin of error for ultra-sound measurement methods, which makes this methodproblematic when monitoring small AAAs. One reasonfor its poor accuracy is the 2D nature of standard ultra-sound measurements, and analyzing a 3D geometric model

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JOURNAL OF VASCULAR SURGERYVolume -, Number - Martufi et al 7

naturally improves the accuracy. The present study useda general geometric analysis of 3D aneurysm models basedon CTA data, which basically would be clinically applicable.However, generating CTA data is not only more expensivethan ultrasound imaging but also exposes patients toionizing radiation and intravenous contrast, which mightnot be suitable for all patients. If CTA scanning is contra-indicated, magnetic resonance angiography or 3D ultra-sound imaging could provide alternative input data forthe proposed multidimensional AAA analysis.

The multiple centerline-based diameter measurementsapplied in this study also provided a comprehensive pictureof the anatomic changes of the aneurysm neck over time,which could influence EVAR treatment decisions. Theaortic diameter at the lowest renal artery was 15% largerthan in a healthy population of the same age and genderratio28 and expanded at 2.4% per year, which is about2.5 times faster than for the normal aorta.28 This resultmight indicate that the neck tissue too is already aneurys-matically altered. Finally, the neck length shortened by anaverage of 6.2% per year, which was accompanied by a slightincrease in neck angulation. These results are confirmed byearlier studies reporting that despite anatomic changes inaortic aneurysm shape, suitability for EVAR and clinicalmanagement do not significantly change at midtermfollow-up.29

CTA is not the standard follow-up modality for smallAAAs, which explains the short follow-up time and thesmall number of patients in this study. This must also beseen as the main study limitation, and a prospective studywith at least 3 years of follow-up and larger sample sizethat takes into account all the baseline characteristics ofpatients and AAAs would be required to get meaningfulinformation for clinical practice, as reported in theliterature.17

Regardless of this shortcoming, our results can becompared with previous results. On the basis of an averagegrowth rate of 4.4%/y from our cohort, a 40-mm AAAwould breach 55 mm at the time t ¼ Ln[55/40]/Ln[1.044] ¼ 7.4 years. Similarly, considering the quartile offast growers in our cohort, we can estimate that 25% of40-mm AAAs would breach 55 mm within <4.5 years.This result correlates nicely with earlier reports.6,30 Ontop of this “average growth analyses,” one might alsoconsider patient individual information to assess the devel-opment of the diameter (based on average and maximumdiameter growth) as well as neck length and angulationdevelopment.

CONCLUSIONS

Clinical trials indicate that surveillance is a safe, cost-effective way of managing small AAAs,1,31-34 with annualor less frequent surveillance intervals for all AAAs <45mm in diameter.17 However, neither maximum diameternor volume measurements over time are able to measurethe fastest diameter growth of the aneurysmatic sac. Asa consequence, expansion-related wall weakening might

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be inappropriately reflected by this type of surveillancedata. In contrast, localized spots of fast diameter growthcan be detected through multiple centerline-based diam-eter measurements over the whole aneurysm sac. Thisinformation might further reinforce the quality of aneu-rysm surveillance programs.

AUTHOR CONTRIBUTIONS

Conception and design: GM, JR, JS, TGAnalysis and interpretation: GM, TGData collection: GM, MA, JR, NS, GPWriting the article: GM, TGCritical revision of the article: JR, JS, NS, GP, TGFinal approval of the article: GM, MA, JR, JS, NS, GP, TGStatistical analysis: GMObtained funding: JS, NS, TGOverall responsibility: TG

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Submitted Aug 21, 2012; accepted Nov 17, 2012.

19 April 2013 � 4:06 pm