Prevalence
of aneurysms and other anomalies of the infrarenal aortic diameter detected
at necropsy
(Portuguese
PDF version)
Erasmo
Simão da Silva1, Allyson Dói2,
Beatriz Yae Hanaoka2, Flavio Roberto Takeda2,
Marcos Hiroshi Ikeda2
1.
Professor of Vascular Surgery, Department of Surgery, School of Medicine
of Universidade de São Paulo (FMUSP).
2. Graduate students, School of Medicine, Universidade
de São Paulo (FMUSP).
Correspondence:
Dr. Erasmo Simão da Silva
Rua Martins, 96
CEP 05511-000 - São Paulo - SP
Tel./Fax: +55 11 3814 9873
E-mail: ersimao@usp.br
Study conducted
in the class of Surgical Technique, Department of Surgery, School of
Medicine, Universidade de São Paulo (FMUSP).
ABSTRACT
Objectives:
To establish the prevalence of anomalies of the infrarenal aortic
diameter detected at necropsy and to compare the prevalence of deaths
caused by cardiovascular disease between patients with anomaly of
the arterial diameter and the control group.
Methods:
Between 1992 and 1995, 645 individuals who were submitted to necropsy
had their abdominal aortas dissected. Variations of arterial diameter
were analyzed in this segment. In order to avoid underestimation
of the aortic diameter, a device that stretches the aortic wall
by means of controlled intraluminal pressure was designed. With
respect to the diameter, aortas were considered as normal, with
aneurysm, ectasia, arteriomegaly or hypoplasia.
Results:
Twenty-nine (4.5%) aneurysms were detected, 25 of them were nonruptured
aneurysms, with diameters smaller than 5.0 cm, and four were ruptured
aneurysms, with diameters larger than 5.0 cm. Nineteen (2.9%) aortic
arteries presented ectasia, 10 (1.6%) presented arteriomegaly, and
there were no cases of hypoplasia. Deaths caused by cardiovascular
diseases were more frequent in individuals with aortic aneurysms
than in the control group (P<0.05).
Conclusions:
The prevalence of anomalies of the infrarenal aortic diameter is
high in a population submitted to necropsy. The aortic dilatations
identified a group of individuals with high probability of death
due to cardiovascular disease.
Key
words: aneurysm, aorta, cardiovascular diseases.
Palavras-chave: aneurisma, aorta, doenças cardiovasculares.
J
Vasc Br 2002;1(2):89-96.
INTRODUCTION
The infrarenal
abdominal aortic segment can present diameter-related vascular anomalies,
such as aneurysm, ectasia, arteriomegaly and hypoplasia; in addition,
it is often involved in the development of obstructive arterial disease.
Among the probable reasons are hemodynamic, histological, biochemical
and anatomical factors.
Infrarenal
aneurysm is the most frequent type of aortic aneurysm; its diameter
is the most important parameter for surgical treatment of patients with
this condition. The clinical importance of arterial ectasia (localized
dilation smaller than the aneurysms) is based on the fact that the lesions
are pre-aneurysm. Arteriomegalies, diffuse dilations of the arteries,
may be associated with episodes of atheroembolism, intermittent claudication
and aortic dissection. Aortic hypoplasias predispose patients to arterial
occlusion and hinder surgical procedures that involve revascularizations
from the aorta, also restricting their duration (Table 1).
 Table
1 - Definition of abdominal aortic diameter disorders
 |
|
Category
(according
to the diameter
of the abdominal aorta)
|
Definition
|
|
|
Ectasia
|
Localized
dilation, with a diameter not exceeding 1.5 times the normal diameter
of the vessel1
|
|
Aneurysm
|
Localized
dilation, with a diameter equal to or greater than 1.5 times
the normal diameter of the vessel1
|
|
Arteriomegaly
|
Diffuse
dilation, associated with tortuosity and elongation2,3
|
Hypoplasia
|
Diameter
smaller than 1.2 cm in adult individuals4
|
|
The aim
of this study is to determine the prevalence of anomalies of the infrarenal
aortic diameter by introducing a prospective methodology, careful surgical
dissection of specimens and aortic distension for reconstitution of
the aortic morphology. The prevalence of cardiovascular deaths was compared
between patients with altered aortic diameter and the control group.
METHODS
From September
1992 and April 1995, 645 dissections of the abdominal aorta were performed
on autopsied corpses at the Division of Postdeath Inspection (Serviço
de Verificação de Óbitos (SVO)) of the School
of Medicine, Universidade de São Paulo. The sample consisted
of 423 (65.6%) male and 222 female individuals. The age ranged between
19 and 97 years, and averaged 55.8 years.
After the
organs were removed from the abdominal cavity for necroscopy by the
pathologist, the aorta was dissected with a surgical technique from
the celiac trunk to its bifurcation. The vessel was removed from the
corpse and the diameter was immediately measured.
No corpse
with longer than 24 hours of death was included in the study. Other
exclusion criteria were presence of infectious and contagious diseases
or no permission of the on-duty pathologist for the procedure. The result
of the examination of the aorta complemented the autopsy report.
A special
device, which allowed for vessel distension, was created for the adequate
measurement of the arterial diameter. The device consisted of a thinner,
firm, perforated probe lined with malleable rubber, which served as
a guidewire to be introduced and passed into the lumen of the vessel.
The probe had two open ends: one of them was covered in malleable rubber
and the other one was connected to a manometer, calibrated in mmHg,
and coupled to a bulb, which injected air and insufflated the rubber
inside the aortic lumen. After aortic distension, the external diameter
was measured with a pachymeter (Figure 1).
Figure
1 - Device for aortic distension.
In this
sample, the vessel was distended until the manometer reached 80 mmHg,
when only one measurement at the point of exit of the inferior mesenteric
artery in the anteroposterior or transversal direction (greater diameter)
was made. When some anomaly, such as ectasia, arteriomegaly or aneurysm
was observed, the larger diameter was measured, independently of the
point of exit of the inferior mesenteric artery.
The following
statistical methods were used: a) arithmetic means and their respective
standard deviations; b) test for equality of means (Student t
test); c) continuity-corrected chi-squared test, according to Yates;
d) significance level of 95% (P < 0.05).
RESULTS
The anomalies
of the aortic diameter were as follows: a) 575 aortas with normal diameters;
b) 29 (4.5%) aortas with aneurysms; c) 19 (2.9%) aortas with ectasia;
d) 10 (1.6%) aortas with arteriomegaly; e) no aorta with hypoplasia.
According to the adopted definitions, 58 (9.0%) aortas revealed abnormal
diameter and were analyzed in this study. Cardiovascular deaths accounted
for 38% of the sample (Table 2).
Table
2 - Deaths caused by cardiovascular diseases in the sampled population
|
|
Causes of death |
Number of cases |
|
|
Acute myocardial infarction |
123 |
|
Stroke |
58 |
|
Heart failure |
40 |
|
Ischemic cardiopathy |
5 |
|
Ruptured abdominal aortic aneurysm |
4 |
|
Ruptured thoracic aortic aneurysm |
2 |
|
Aortic dissection |
13 |
|
Mesenteric ischemia |
3 |
|
Among the
29 aneurysms observed (prevalence of 4.49% - Figure 2), the mean age
was 69.4 years (49 to 97 years). White individuals, 27 (93.1%), and
male individuals, 22 (75.9%) prevailed. If the sample is limited to
the target population for aneurysmal disease, that is, age over 49 years
(age of the youngest individual with aneurysm), the prevalence rises
to 6.9% in 420 cases.
Figure
2 -Infrarenal abdominal aortic aneurysm
with reconstructed morphology.
In this
group, cardiocirculatory diseases represented 65.5% of deaths. The comparative
study between causes of death in this group and in individuals without
pathological dilations shows there exists a predominance (with statistical
significance, P < 0.05) of cardiocirculatory deaths among
those individuals with aneurysm (Table 3).
Table
3 - Cardiovascular deaths in the control groups and in patients with
aneurysms
|
|
Groups |
#
of cases |
#
of cardiovascular deaths |
% |
X2c |
Number of cases |
|
|
Controls |
575 |
204 |
35.50 |
9.45 |
P>0.05 |
|
Aneurysm |
29 |
19 |
65.50 |
|
|
|
X2c
= Chi-squared
test
The maximum
diameter of aneurysms ranged from 2.8 cm to 9.5 cm. In 20 cases (69%
of the aneurysms) the maximum diameters were considered to be small
(smaller than 4.0 cm). Diameters between 4 cm and 5 cm showed a prevalence
of 13.8% (four cases); diameters greater than 5 cm corresponded to 17.2%
(five cases). In the latter group, four ruptured aneurysms (13.8% of
the whole sample) were included. Among the ruptured aneurysms, diameters
of 5.8 cm, 7.5 cm, 8.2 cm and 9.5 cm were observed.
The histological
findings in the analyzed aneurysms ruled out inflammatory, traumatic,
poststenotic, or mycotic etiologies. All of them showed histological
characteristics compatible with nonspecific etiology and with secondary
arteriosclerotic disorders.
The prevalence
of ectasia of the infrarenal aorta was 2.9% (19 cases) (Figure 3). The
mean age was 62.9 years (42 to 86 years), with a prevalence of 57.9%
of male individuals (11 cases).
Figure
3 - Ectasia of the distal segment of
the abdominal aorta at the point of exit of the inferior mesenteric
arteryn.
The greatest
diameter was 2.6 cm and the smallest one was 1.7 cm. Cardiovascular
diseases, especially acute myocardial infarction (36.8%), accounted
for most deaths (57.9%); however, no statistical significance was observed
when the causes of death were compared with the rest of the sample (Table
4).
Table
4 - Cardiovascular deaths in the control groups and in patients with
ectasia
|
|
Groups |
#
of cases |
#
of cardiovascular deaths |
% |
X2c |
significance |
|
|
Controls |
575 |
204 |
35.50 |
3.09 |
N.S. |
|
Ectasia |
19 |
11 |
57.90 |
|
|
|
X2c
= Chi-squared
test; N.S. = not significant
Arteriomegaly
was detected in 10 individuals (1.6%). The mean age was 73.8 years (56
to 85 years), with a male predominance of 90% (9 cases). The smallest
diameter was 2.3 cm and the largest one was 2.8 cm.
Seven deaths
(70%) were caused by cardiovascular diseases, two of which occurred
due to aortic dissection (20%). No statistical significance was observed
as to the cause of cardiovascular death when compared with the sample
(Table 5).
Table
5 - Cardiovascular deaths in the control groups and in patients with
arteriomegaly
|
|
Groups |
#
of cases |
#
of cardiovascular deaths |
% |
X2c |
significance |
|
|
Controls |
575 |
204 |
35.50 |
3.69 |
N.S. |
|
Arteriomegaly |
10 |
07 |
70.00 |
|
|
|
X2c
= Chi-squared
test; N.S. = not significant
DISCUSSION
The great
limitation of the studies involving the measurement of vascular diameter
at necropsy lies in the lack of vascular distension pressure after death.5,6
With the aim of partially solving such limitation, the present study
proposes the use of a device to measure the aortic diameter. This device
reconstructs the aortic morphology.
The option
for studying the arterial aortic diameter at necropsy is based on the
fact that anatomy is a major form of morphological analysis, and the
data obtained through the observations and anatomical measurements are
the basis for other diagnostic methods applied to clinical practice.
These methods also have limitations. Arteriography underestimates vascular
diameter,4 due to the presence of mural
thrombus or thickening of the tunica intima. Ultrasonography, a noninvasive
diagnostic method that revolutionized the diagnosis of aneurysms,7-11
shows important variability depending on the experience of the examiner.
Similarly, when surgical and tomographic measurements are compared with
ultrasound measurements, we observe differences that can reach 0.5 cm
and, roughly speaking, 1.0 cm.12,13
At computed tomography, the measurements are also subject to failures,
for instance, the overestimation of a tortuous aortic diameter.14
The measurements made by nuclear magnetic resonance, also quite accurate,
are restricted due to the availability and costs.
Even small
diameter alterations can be detected when the vessel is distended after
the aortic dissection, such as blebs, ectasia, arteriomegaly and small
aortic aneurysms. With these data, we can determine the prevalence of
these disorders in a population submitted to necropsy.
Vascular
physiology studies reveal that the arterial pressure curves versus arterial
vascular diameter are not linear, that is, from a given pressure value,
the aorta becomes nondistensible.15-17
This value occurs at some point between 80 mmHg and 120 mmHG,15
and varies with age and with the presence of atherosclerosis. By analyzing
these data and using the pilot analysis described herein, we opted for
using a distension pressure of 80 mmHg.
The aneurysmal
disease was described, its etiology was studied and the disease was
mapped in terms of morphological types and affected aortic segments
by observation at necropsy. Several necropsy studies contributed to
the understanding of the natural evolution and to the determination
of the prevalence of aneurysms.
Two important
issues comprised by the data analysis in this study were: first, the
increase of the prevalence of infrarenal aneurysms; secondly, the aortic
diameter and the possibility of aneurysm rupture. The prevalence of
infrarenal aneurysm was high (4.5%). Literature reviews show that the
prevalence varies between 0.85% and 8.1% in necropsy samples (Table
6).
Table
6 - Prevalence of infrarenal aneurysm at necropsy
|
| Author |
Country |
Year |
Prevalence |
Sample |
|
| Turk17
|
UK |
1965 |
3.00% |
1,544 |
| Darling
et al.18 |
USA |
1977 |
2.00% |
24,000 |
| Rantakokko
et al.19 |
Finland |
1983 |
0.85% |
22,765 |
| Johnson
et al.20 |
USA |
1985 |
2.40% |
1,665 |
| Mcfarlane21
|
USA |
1991 |
1.70% |
7,297 |
| Bengtsson
et al.22 |
Sweden |
1992 |
3.20% |
45,838 |
|
Both in
necropsy studies and in research on the detection of aneurysms in living
patients, the prevalence increases if the sample is selected according
to sex, age and clinical condition. Table 7 shows the prevalence of
infrarenal aneurysms among living patients by means of ultrasonography
or computed tomography.
Table
7 - Prevalence of infrarenal aneurysm in living patients
|
| Author |
Country |
Year |
Age
(years) |
Sex |
Prevalence |
|
| Johnson
et al.20 |
USA |
1985 |
>
50 |
M
and F |
2.50% |
| Collin
et al.23 |
UK |
1988 |
65
to 74 |
M |
5.40% |
| Akkersdijk
et al.7 |
Holland |
1991 |
>
50 |
M
and F |
4.90% |
|
|
|
>
60 |
M
and F |
11.40% |
| Scott
et al.11 |
UK |
1991 |
65
to 80 |
M
and F |
4.30% |
| Lucariotti
et al.24 |
UK |
1992 |
>
65 |
M |
2.50% |
| Bonamigo25
|
Brazil |
1995 |
>
75 |
M |
3.20% |
|
Brazil |
1995 |
mean
74 |
M |
3.10% |
|
|
|
|
F |
0.40% |
|
The differences
between prevalence rates in the present study and those in other studies
can be explained in different ways: a) the study sample has a demographic
selection (more men, more whites and more elderly individuals) and a
clinical selection (high prevalence of cardiovascular diseases at the
SVO); b) the study was conducted in a prospective manner; c) the definition
of abdominal aortic aneurysm was applied individually by comparing the
dilation with the aortic segment that was normal in terms of diameter;
d) the employed method, aortic distension with intraluminal pressure,
diagnoses small aneurysms, which would not be detected if the aorta
were hollow at the moment of analysis.
The pioneering
necropsy studies with significant population samples showed a very low
prevalence of the disease, between 0.29% in 190526
and 0.32% in 1936.27 Some decades after
these reports and with the epidemiological control of syphilis, Estes28
(1950) and Shatz et al.29 (1962) already
showed a higher frequency, with a change in the profile of the disease
(older patient population and predominantly arteriosclerotic etiology).
By comparing different periods, in a relatively isolated population
in western Australia, Castleden et al.30
(1985) showed that, between 1971 and 1981, the prevalence increased
from 74.8 per 100,000 to 117.2 per 100,000. Bickerstaff et al.,31
in 1984, concluded that between 1950 and 1980, the incidence of infrarenal
aneurysms had a sevenfold increase. In Brazil, Bonamigo,25
in 1995, detected a rate of 3.2% among males aged over 75 years.
The aneurysm
diameter is the most important isolated factor for deciding on the surgical
or expectant treatment of aneurysm patients. However, the medical literature
on aneurysms smaller than 5.0 cm is controversial.
The present
study shows a high prevalence (69%) of aneurysms considered to be small
(diameter smaller than 4.0 cm). These data show that such aneurysms
are common findings in patients with severe cardiovascular diseases
(major cause of death in the group). As to the natural evolution, the
aneurysms can be considered safe in terms of rupture in the studied
sample, since none of them ruptured, differently from aneurysms with
a diameter greater than 5.0 cm, which ruptured in four cases, a total
of five (14% of rupture among all the detected aneurysms). Despite the
small number of cases with larger aneurysms and variability of the diameter
at which they ruptured, the sample revealed that aneurysms up to 5.0
cm are not prone to rupture.
These data
are different from the classical study conducted by Darling et al.18
in 1977, which, in spite of analyzing a very large sample (24,000 necropsies),
conducted a retrospective study. The rate of rupture of aneurysms smaller
than 4.0 cm was 9.5%. The authors also detected a similar rate of rupture
for aneurysms with a diameter between 4.1 and 5.0 cm (23.4%) and between
5.1 and 7.0 cm (25.3 %), which is surprising, since the tendency towards
rupture is very high in larger aneurysms.
The method
used in the present analysis allowed ectasias to be detected (prevalence
of 2.9%), since they would not be identified if the aorta were studied
with no pressure. The meaning of this alteration is relevant, since
this is a pre-aneurysm formation. In addition, although the mean age
of patients was better than that of the patients with aneurysms, acute
myocardial infarction was the major cause of death in this group.
Leriche,32
in 1943, described the clinical, arteriographic and surgical finding
of patients with dilated, elongated, and tortuous arteries, calling
them dolicho and mega-arteries. Thomas,3
in 1971, suggested the name arteriomegaly. As clinical manifestation,
intermittent claudication (due to slow blood flow) and atheroembolism
may occur. Johnston et al.33 defined the condition as a diffuse dilation
of the aorta, whose diameter is greater than or equal to 2.5 cm. In
this sample, the age (mean of 73.8 years) draws our attention, since
it was higher than that of other groups, in addition to the association
with aortic dissection (20%), which confirms this tendency.2,3
No individual
with hypoplasia of the abdominal aorta was found, in contrast to the
study carried out by Arnot et al.34 (1973), also at necropsy. The authors
mentioned above specifically studied the posterior wall of the abdominal
aorta in an attempt to confirm the congenital hypothesis on the etiology
of hypoplasia, the superfusion of the primitive dorsal aorta in the
fourth week of embryonic life. The fundamental difference between the
two necropsy studies was the restoration of aortic pressure.
Other reports
involving arteriography in patients with peripheral atherosclerosis
define hypoplasia by the contrast diameter,4,35
disregarding the thickening of the tunica intima or the presence of
mural thrombus. In the methodology used in the present study, the external
diameter was measured; therefore, it is not underestimated by the disease
in the aortic tunica intima.
In conclusion,
the prevalence of abdominal aortic dilations observed at necropsy is
high, especially in a sample with high incidence of cardiovascular diseases
and in a prospective study that aims at the specific investigation of
these disorders in order to reconstruct the aortic morphology after
death.
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