© 2010 Canadian Medical Association Can J Surg, Vol. 53, No. 1, February 2010 25
RESEARCH • RECHERCHE
Morphometric analysis of anatomic variables
affecting endovascular stent design in patients
undergoing elective and emergency repair of
endovascular abdominal aortic aneurysm
Background: Our objective was to identify morphologic trends in elective and emer-
gency endovascular aneurysm repair (EVAR). This work will inform hospitals with
endovascular programs about the diameters and lengths of endostents that should be
available to efficiently care for patients with these conditions.
Methods: We performed a retrospective review of patients undergoing elective
(n = 127) and emergency (n = 17) EVAR. Using computed tomography and 3-dimensional
reconstructions, we evaluated the following: diameters of the aneurysm (D3), the aorta
at the superior mesenteric (D1) and renal (D2a,b,c; 3 levels) levels, the iliac arteries
(D5a,b; right and left) and the aortic bifurcation (D4); lengths from the lowest renal
artery to the distal aspect of the aortic neck (H1), to the aortic bifurcation (H3), to the
right and left iliac bifurcations (H4a,b); and angles of the origin of the common iliac
arteries on the transverse plane (A1). We used descriptive statistics of trends within
groups and independent sample t tests.
Results: In elective and emergency aneurysm repair, D2max (26, standard deviation
[SD] 3, mm v. 30.7 [SD 3] mm), D5a (16 [SD 4.7] mm v. 19.3 [SD 5] mm), D5b (15.3
[SD 4] mm v. 18.1 [SD 3.6] mm), H1 (25.6 [SD 8.6] mm v. 18 [SD 2] mm), H4a (173
[SD 22] mm v. 189.5 [SD 22] mm) and H4b (174 [SD 25] mm v. 190 [SD 14] mm)
were significantly different between the 2 groups (p = 0.001, p = 0.006, p = 0.007,
p < 0.001, p = 0.05 and p = 0.01, respectively). H3 (118 [SD 17] mm v. 121.5 [SD 13.5]
mm) was not significantly different (p = 0.40). In elective patients, A1 identified the
right common iliac more frequently anterior relative to the left common iliac (mean
23°, SD 16°).
Conclusion: Significant anatomic differences between elective and emergency
patients will require hospitals to stock separate endovascular devices to treat abdom -
inal aortic aneurysms in both groups.
Contexte : Nous voulions dégager des tendances morphologiques dans la réparation
endovasculaire d’un anévrisme (REVA) élective et d’urgence. Ce travail informera les
hôpitaux qui ont des programmes endovasculaires au sujet du diamètre et de la
longueur des endostents qui devraient être disponibles pour traiter efficacement les
patients qui ont ces problèmes.
Méthodes : Nous avons procédé à une étude rétrospective des dossiers des patients
qui ont subi une REVA élective (n = 127) et d’urgence (n = 17). On a utilisé la tomo -
densitométrie et des reconstructions tridimensionnelles pour évaluer les aspects sui -
vants : diamètres de l’anévrisme (D3), aorte aux niveaux mésentérique supérieur (D1)
et rénal (D2a,b,c; 3), artères iliaques (D5a,b; droite et gauche) et bifurcation de l’aorte
(D4); longueurs entre l’artère rénale la plus basse jusqu’à l’aspect distal du col de
l’aorte (H1), à la bifurcation de l’aorte (H3) et aux bifurcations iliaques droite et
gauche (H4a,b); ainsi qu’angles de l’origine des artères iliaques communes sur le plan
transversal (A1). Nous indiquons les diamètres et les longueurs en millimètres et nous
avons utilisé des statistiques descriptives des tendances à l’intérieur de groupes et des
tests t sur échantillonnage indépendants.
Résultats : Dans les cas de réparation élective et d’urgence d’un anévrisme, D2max
(26 mm, écart-type [ET] 3 c. 30,7 [ET 3] mm), D5a (16 [ET 4,7] mm c. 19,3 [ET 5]
mm), D5b (15,3 [ET 4] mm c. 18,1 [ET 3,6] mm), H1 (25,6 [ET 8,6] mm c. 18
[ET 2] mm), H4a (173 [ET 22] mm c. 189,5 [ET 22] mm) et H4b (174 [ET 25] mm
c. 190 [ET 14] mm) présentaient une différence significative entre les 2 groupes
Michael Kilian, BHSc (Hon)
Wilfred Dang, BHSc (Hon)
Claudio S. Cinà, MD
From the Division of Vascular Surgery,
St. Michael’s Hospital, University of
Toronto, Toronto, Ont.
Accepted for publication
July 13, 2008
Dr. C.S. Cinà
Division of Vascular Surgery
University of Toronto
St. Michael’s Hospital
55 Queen St. E, #308
Toronto ON MSC 1R6
responsible for about 1658 deaths per year.5A population-
based study has shown that 66% of patients with ruptured
AAAs die before undergoing operative repair.6The risk of
rupture increases with AAA size from 1% per year for a
diameter of 4.0–4.9 cm to 26% for a diameter greater than
6.0 cm.7–9Screening, timely treatment and reduction in peri-
operative mortality will reduce the burden of this disease.5
Until recently, repair of AAAs required invasive open
surgery. This resulted in perioperative mortality of
5%–8%10–15and risk of complications of 15%–20%.16
Endovascular aortic aneurysm repair (EVAR) is an accepted,
minimally invasive modality of treatment with reduced peri-
operative mortality of 1%–2%16–18and risk of complications
of 5%–10%.16Although certain anatomic criteria must be
satisfied, a significant proportion of patients (40%–60%) is
eligible for EVAR.19,20To fit a patient’s anatomy, EVAR
relies on customized modular stents that are deployed at the
site of the aneurysm to divert blood flow from the weakened
walls of the aneurysm.20–22The components available for
EVAR are so numerous that more than 65 000 combina-
tions may be possible using components from a single
manu facturer. This number will increase exponentially if
hybrid endografts, made of components derived from multi-
ple manufacturers, are also considered. The cost of these
endovascular grafts limits the applicability of this treatment
and is a serious consideration for hospitals, which need to
stock a large number of components for patients undergoing
elective and emergency EVAR.
This study defines trends in aortoiliac anatomic mea-
surements in patients undergoing elective and emergency
EVAR. The results may be used by hospitals to improve
cost-efficiency by stocking a limited number of devices and
permitting expansion of existing endovascular programs or
facilitating the development of new ones. In addition, the
results of this study may inform the industry to optimize the
production of stents in terms of diameters, lengths and con-
figurations, and possibly improve graft hemodynamics.
bdominal aortic aneurysms (AAAs) are more
prevalent among men than among women over 64
years of age (6% v. 1%).1–4In Canada, AAAs are
We performed a retrospective review of prospectively
collected data of consecutive patients undergoing elective
and emergency EVAR from October 2004 to December
2007 in a tertiary vascular centre. We defined ruptured
aneurysms as displaying extravasation of contrast outside
the limits of the aortic wall. This study received institu-
tional ethics approval.
To determine the most common anatomic measure-
ments of elective EVAR patients, we evaluated aortoiliac
diameters, lengths and angles. We measured aortic diam -
eters at the superior mesenteric (D1), proximal, middle and
distal levels of the infrarenal aortic neck (D2a,b,c), the
widest section of the abdominal aneurysm (D3) and the
region immediately proximal of the aortic bifurcation (D4).
We assessed diameters of the right and left common iliac
26 J can chir, Vol. 53, No1, février 2010
Fig. 1. Aortoiliac anatomic measurements. Note: D1 = diameter
of the superior mesenteric artery; D2a,b,c = diameter at the proxi-
mal, middle and distal levels of the infrarenal aortic neck, respec-
tively; D3 = diameter at the widest section of the abdominal
aneurysm; D4 = diameter at the region immediately proximal of
the aortic bifurcation; D5a,b = diameters of the right and left com-
mon iliac arteries, respectively; H1 = length from the lowest renal
artery to the distal aspect of the aortic neck; H3 = length from the
lowest renal artery to the aortic bifurcation; H4a,b = length from
the lowest renal artery to the right and left iliac bifurcations,
respectively; H5a,b = length from the lowest renal artery to the
right and left external iliac arteries, respectively.
(p = 0,001, p = 0,006, p = 0,007, p < 0,001, p = 0,05 et p = 0,01 respectivement). Il n’y
avait pas de différence significative pour H3 (118 [ET 17] mm c. 121,5 [ET 13,5] mm)
(p = 0,40). Chez les patients qui ont subi une intervention élective, A1 identifiait
l’artère iliaque commune droite plus souvent en position antérieure par rapport à
l’artère iliaque commune gauche (moyenne de 23°, ET 16°).
Conclusion : Les différences anatomiques importantes entre les patients qui subis-
sent une intervention élective et une intervention d’urgence obligeront les hôpitaux à
stocker des dispositifs endovasculaires distincts pour traiter les anévrismes de l’aorte
abdominale chez les 2 groupes.
Can J Surg, Vol. 53, No. 1, February 2010 27
arteries (D5a,b) at the estimated landing zone. We mea-
sured lengths from the lowest renal artery to the distal
aspect of the aortic neck (H1), the aortic bifurcation (H3),
the right and left iliac bifurcations (H4a,b) and the right
and left external iliac arteries (H5a,b) in patients who
required landing in the external iliac artery (Fig. 1). Using
the proximal, middle and distal measurements (D2a,b,c),
we defined the shape of the aortic neck as cylindrical,
flared, reversed flare or hourglass. We used a change in
diameter of greater than 10% between the most proximal
and most distal measurements as the threshold for classifi-
cation. A flared neck implied that the distal diameter was
larger, whereas a reversed flare assumed the opposite con-
figuration. For patients in the emergency EVAR group, we
did not measure D1, D3, D4, H5a and H5b given the
emergency of the settings and the fact that these variables
were not relevant to choose the appropriate stent graft.
In addition, we described the position of the origin of
the common iliac arteries relative to each other and
expressed the relation as an angle on the transverse plane
(A1). To accomplish this measurement, we established the
estimated centre of the right common iliac artery as the
origin of the angle. From this origin, 2 lines, one horizon-
tal and one through the estimated centre of the left com-
mon iliac artery (LCIA), were drawn. The position of the
LCIA was defined in degrees of an angle. We described
the angle as positive if the LCIA was anterior, and negative
if the LCIA was posterior in relation to the right common
iliac artery (RCIA). We defined an angle of 5° or less in
either direction as an angle of zero, and we considered
both arteries to be in the same plane (Fig. 2).
Between October 2004 and September 2006, we took
measurements of elective EVAR from axial scans with slice
thickness ranging from 5 to 3 mm, and reconstructions
created with 1.5-mm overlap. Starting in September 2006,
we assessed measurements using computed tomography
(CT) scans obtained with a 64-slice scanner and postpro-
cessing with an Aquarius workstation v. 3.5 (TeraRecon
Inc.). The senior vascular surgeon (C.S.C.) obtained all
measurements, which were entered in a specifically
designed planning form. We performed measurements of
diameters from adventitia to adventitia, and we estimated
lengths using centre line reconstructions (Fig. 3).
We obtained emergency EVAR measurements from
axial CT scans generated from 8- to 64-slice scanners
while the patient was being prepared for surgery. In each
case, the senior vascular surgeon (C.S.C.) evaluated the
appropriate variables. We assessed measurements using
different CT readers according to availability. In this
group of patients, the diameter measurements could usu-
ally be assessed accurately from the available imaging tech-
niques. Lengths were often estimated by a combination of
tomographic imaging and intraoperative angiography.
Three investigators entered measurements into a data-
base. At least 2 investigators were present at each session to
minimize errors associated with entering the variables and
to discuss any disagreements that arose during the process.
Investigators resolved any remaining disagreements
through discussion with the senior author (C.S.C.).
Excluded from the analysis were thoracic (n = 25) and tho-
racoabdominal (n = 12) aneurysms. We conducted statisti-
cal analysis using SPSS software v.15.0. We expressed
diameters, lengths and angles in millimetres and as means
and standard deviations (SDs), and we used the maximum
Fig. 2. A computed tomography scan showing the angle used to
define the relative position of the iliac arteries: centre of the right
common iliac artery (A) and centre of the left common iliac artery (B).
Fig. 3. Centre line measurements in a stretched view of the aorta
(left) and in 3-dimensional rendering (right): H1 (neck of the
aneurysms) is 45.60 mm; H3 (distance between the lowest renal
artery and the aortic bifurcation) is 121.89 mm; and H4a (distance
from the lowest renal artery to the iliac bifurcation) is 203.15 mm.
28 J can chir, Vol. 53, No1, février 2010
and minimum values to represent the range of measure-
ments for each variable. We calculated the mode, with the
number of counts it appeared for each measurement, to
determine the most frequent dimensions.
We calculated missing data points for elective patients
by linear interpolation for all variables excluding D1.23This
involved averaging the values closest to (e.g., above and
below) the missing data point to provide an estimate of the
missing value. We interpolated the missing H5a,b values
when the patients’ operative report showed an external iliac
landing zone. We estimated missing D1 values using the
largest of the 3 aortic neck diameters D2a,b,c (D2max).
We deemed this a more accurate technique over interpola-
tion owing to the proximity of the 2 measurements in rela-
tion to the patient’s anatomy.
We used independent sample 2-tailed t tests to compare
variables when the assumption of equality of variances
(Levene test) was satisfied, and we applied an appropriate
correction when this assumption was not satisfied. We
used a Fisher exact test to evaluate categorical variables and
considered p ≤ 0.05 significant.
Overall, 158 patients underwent EVAR. Data were not
available for 12 patients undergoing elective EVAR and for
2 patients with ruptured aneurysms, leaving 144 patients
for evaluation (127 elective and 17 emergency). One hun-
dred elective patients were selected for the analysis of A1.
Among the included elective patients, missing values per
variable were as follows: D1 = 56, D3 = 22, D4 = 21, D5a =
8, D5b = 5, H3 = 14, H4a = 4, H4b = 9, H5a = 2, H5b = 2.
There were no missing values for D2 and A1. No missing
values were present among the emergency patients. Table 1
and Table 2 describe the variables for elective and emer-
gency patients, respectively. Table 3 contains the results of
the independent samples t tests comparing the 2 groups.
Among elective patients, D1 had a mean diameter of 26.3
(SD 3.2, range 21) mm. The most frequent measurement
of 28 mm occurred 22 times among the sample population.
The average largest aneurysm diameter (D3) in the elective
group was 60 mm (SD 8.7, range 55, mode 55 mm, count
= 20). D4 mean was 28.9 mm (SD 7.9, range 45; modes 22
and 25 mm, each with a count of 11).
Maximum aortic neck diameter (D2max) and
diameter of right and left common iliac arteries (D5a,b)
D2max was smaller in the elective compared with the
emergency group (26.2, SD 3.0, range 21 mm v. 30.7,
SD 3.4, range 14 mm; p < 0.001). The most frequent
D2max measurements were 28 mm and 31 mm, occurring
in 23 elective and 6 emergency patients, respectively. No
significant difference was found between D1 and D2max
measurements in the elective group (p = 0.90).
In elective patients, D5a and D5b were 15.9 (SD 4.7,
range 34) mm and 15.4 (SD 3.8, range 30) mm, respec-
tively. The mode for both D5a and D5b was 15 mm, with
Table 3. Comparison of results of independent sample t tests
in patients undergoing emergency v. elective endovascular
abdominal aortic aneurysm repair
6.00 to 2.90
5.80 to 1.00
4.60 to 0.70
–4.99 to –8.73
12.00 to 5.30
27.30 to 4.90
28.10 to 3.50
CI = confidence interval; sig. = significance.
*Test for equality of variance.
†Emergency compared with elective endovascular abdominal aortic aneurysm repair.
Table 1. Descriptive statistics for patients undergoing
elective endovascular abdominal aortic aneurysm repair
Mean (SD) Mode Maximum Minimum
N/A = not applicable; SD = standard deviation.
*Diameters and lengths are expressed in mm; see Fig. 1 for description of the variables.
†The largest of the 3 D2(a,b,c) is reported.
‡Expressed in degrees of an angle.
§Multiple modes exist (the smallest is shown).
¶Measurements appeared only once per group.
Table 2. Descriptive statistics for patients undergoing
emergency endovascular abdominal aortic aneurysm repair
Mean (SD) Mode Maximum Minimum
SD = standard deviation.
*Diameters and lengths are expressed in mm.
†Multiple modes exist (the smallest is shown).
Can J Surg, Vol. 53, No. 1, February 2010 29
counts of 18 and 21, respectively. Diameters were greater
in the emergency group: 19.3 (SD 4.97, range 18) mm
(p = 0.006) and 18.1 (SD 3.6, range 13) mm (p = 0.007),
respectively. Among emergency patients, the most fre-
quent measurements were 19 (count = 3) and 20 mm
(count = 4) for D5a and D5b, respectively.
Lengths of aortic neck (H1)
H1 was greater in the elective than in the emergency
patients (25.7 [SD 8.6, range 46] mm v. 18.8 [SD 2.25,
range 7] mm; p < 0.001); modes were 20 mm (count = 29)
and 19 mm (count = 4), respectively.
Length from lowest renal artery to aortic
H3 was 118.1 (SD 17.3, range 111) mm in the elective and
121.5 (SD 13.5, range 50) mm in the emergency group
(p = 0.40); modes were at 110 (count = 17) and 111 mm
(count = 3), respectively.
Lengths from lowest renal artery to right and left
iliac bifurcations (H4ab)
There was no difference between H4a and H4b among elec-
tive patients, as the analysis yielded measurements of 173.4
(SD 21.6, range 132) mm and 174.4 (SD 25, range 230) mm,
respectively. The mode for H4a was 160 mm (count = 11)
and 2 modes were present for H4b, 160 and 170 mm (each
with a count of 12). In the emergency group, H4a and H4b
were greater than in the elective group: 189.5 (SD 22.3,
range 86) mm (p = 0.05) and 190.2 (SD 14.1, range 43) mm
(p = 0.012), respectively. In the emergency group, the mode
for H4a was 187 mm (count = 3), and 2 modes were present
for H4b, 176 and 210 mm (each with a count of 3).
Lengths from lowest renal artery to right and left
external iliac landing zones (H5ab)
H5a and H5b were 235.8 (SD 31.9) mm and 227.8 (SD 23.4)
mm among elective patients, respectively. Modes are not pre-
sented since measurements occurred only once per variable.
Angle of origin of common iliac arteries (A1)
and shape of the neck
In the elective group, the most common configuration
regarding the angle of origin of the common iliac arteries
involved the RCIA being anterior relative to the LCIA
(23.1°, SD 16°, range 61°). No patients were found to
have the opposite configuration.
In elective patients, a cylindrical configuration of the
neck was the most commonly represented. This distribu-
tion was reversed in the emergency group, in which the
flared neck was represented in greater number than in the
elective (p ≤ 0.001) (Table 4).
Accurate assessment of aortic and iliac morphology is
important in endovascular graft design. A review of 18 cen-
tres in Australia has shown that aneurysm morphology can
be predictive of outcome, finding aneurysm neck lengths of
less than 10 mm to be associated with endoleaks (odds ratio
8.3, 95% confidence interval 8.0–8.6).24
We have shown that elective patients undergoing EVAR
frequently have neck diameters of 26–28 mm. Hence,
endovascular stents with a diameter of 28–32 mm are likely
to cover a large range of anatomies. In cases of ruptured
aneurysm, the size of the patient’s neck is larger and the
length shorter than in cases of elective EVAR. Most emer-
gency patients were found to have a neck diameter in the
30–31 mm range, requiring larger stents of 35–36 mm in
diameter. Although there was a slight increase in the length of
H3 for ruptured aneurysms, this did not reach statistical sig-
nificance. Iliac arteries were of greater length and diameter
in the ruptured group compared with the elective group. The
relevance of these findings is that main bodies with similar
lengths may be kept in inventory for both groups, whereas leg
extensions to deal with iliac arteries of 70–80 mm in length and
19–20 mm in diameter are necessary for ruptured aneurysms.
Previous studies have described aortic and iliac trends in
patients with AAAs and have compared the quality of dif-
ferent imaging techniques used to measure ana tomic vari-
ables in these individuals. There have been a limited num-
ber of studies evaluating these variables in ruptured AAAs
and even fewer that undertook a comprehensive anatomic
evaluation of all relevant variables using dedicated postpro-
cessing software of CT images.
Beebe and colleagues,25using a retrospective review of
CT images and cut plain traditional contrast angiography,
conducted an anatomic study in 50 patients with AAAs
who did not undergo EVAR. They found that average
neck diameters were 29 (SD 0.7) mm by CT and 26
(SD 0.56) mm by angiography. The difference in measure-
ments is explained by the fact that angiography is only able
to image the inner lumen of the vessel. The average H3
Table 4. Shape of neck distribution
in patients undergoing elective
and emergency endovascular
abdominal aortic aneurysm repair
Surgery; no. of patients
Shape of neck Elective Emergency
*p < 0.001.