AJR 2004; 182:875-879
© American Roentgen Ray Society
Abdominal CT Angiography Before Surgery as a Predictor of Postoperative Death in Acute Aortic Dissection
Hélène Vernhet1,
Jean Michel Serfaty1,
Mohamad Serhal1,
Eugene McFadden1,
Eric Bonnefoy2,
Patrice Adeleine3,
Didier Revel1 and
Philippe Douek1
1 Department of Thoracic and Cardiovascular Imaging, Louis Pradel Hospital, 59,
Blvd. Pinel, Lyon 69394, France.
2 Surgical Intensive Care Unit, Louis Pradel Hospital, Lyon 69394, France.
3 Department of Biostatistics, Louis Pradel Hospital, Lyon 69394, France.
Received April 25, 2003;
accepted after revision October 2, 2003.
Address correspondence to P. Douek.
Abstract
OBJECTIVE. The purpose of our study was to search for a relationship
between postoperative death in acute aortic dissection and abdominal helical
CT findings before surgery.
MATERIALS AND METHODS. We retrospectively included 48 patients
admitted to our institution for emergent surgery of acute aortic dissection
diagnosed with helical CT angiography. We recorded postoperative deaths and
analyzed abdominal helical CT vessels and parenchymal abnormalities, including
the presence of dissected abdominal aortic branches, a compressed aortic
lumen, and low enhancement of the parenchyma in abdominal organs.
RESULTS. Among the 48 patients, 11 died after surgery. Postoperative
death occurred in one of five patients with low enhancement of the parenchyma
in one abdominal organ and in seven of eight patients with low enhancement of
the parenchyma in at least two abdominal organs. The postoperative death rates
strongly correlated with the number of low-enhanced abdominal organs per
patient (p < 0.00005) but did not correlate with the number of
dissected abdominal aortic branches.
CONCLUSION. The rate of abdominal organs with low enhancement of the
parenchyma seen on CT before surgery is a strong factor in outcome in patients
with acute aortic dissection. Additional analysis of low enhancement of the
parenchyma in abdominal organs on CT might be a useful tool to detect, before
surgery, patients at risk of postoperative death.
Introduction
Aortic dissection involving the ascending aorta requires urgent surgery,
whereas dissection sparing the ascending aorta is generally managed medically.
For both types of dissection, delayed mortality caused by organ underperfusion
is a major determinant of accurate prognosis. When an ischemic complication is
clinically diagnosed, the mortality rate is 50% in patients with type I or II
dissection and 28–67% in patients with type III dissection
[1–5].
Minimally invasive endovascular approaches have been developed to manage such
complications, with promising results in selected patients
[6]. However, the success of
such procedures is still dependent on early diagnosis
[7].
Transesophageal echocardiography is the technique of choice for the
diagnosis of aortic dissection in many centers
[8]. This imaging technique,
available at the bedside, can assess the presence of an intimal flap in the
ascending aorta and the need for emergent aortic surgery. Unfortunately, with
transesophageal echography, exploration of the aorta is limited to the
thoracic aorta and is blind to abdominal organs.
CT can depict aortic dissection with a 100% reported sensitivity and
specificity [9,
10] and can scan the entire
aorta, the visceral vascular bed, and the surrounding organs. The purpose of
our study was to evaluate whether postoperative death in acute aortic
dissection correlates with dissection of abdominal organ branches, compression
of the aortic lumen, or low enhancement of abdominal organs, all seen on CT
before surgery.
Materials and Methods
From January 1995 to December 2000, 60 patients with acute aortic
dissection were referred to our institution for emergency surgery after the
diagnosis was confirmed on helical CT. There were 42 men and 18 women with a
mean age of 63 years (age range, 26–85 years). According to the De Bakey
classification [11], the
dissections were classified as type I in eight patients, type II in 42
patients, and type III in 10 patients. Because our institution is the regional
referral center for aortic surgery, only patients with complicated (i.e.,
suspicion of aortic rupture or ischemic complication) type III dissection were
referred to our hospital. Twelve patients with CT angiography performed before
their transport to our institution died of aortic rupture between their
arrival at our institution and surgery
(Table 1). These 12 patients
were excluded from CT analysis. The 48 remaining patients with aortic
dissection seen on helical CT angiography were included in this study.
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TABLE 1 CT Extension of the Dissection Type (De Bakey Classification
[11]) and Number
of Patients with Immediate and Early Clinical Outcomes
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We retrospectively analyzed helical CT images of these 48 patients. Helical
CT was performed using scanners from various manufacturers because patients
arrived at our institution having already undergone CT. CT parameters that
were identical among centers were the following: entire coverage of the
thorax, abdomen, and pelvic area; and slice thickness inferior or equal to 5
mm. Injection parameters were the following: 120–150 mL of contrast
media with an injection rate ranging from 3 to 4 mL/sec. Delay between
injection and acquisition averaged 30 sec. Images photographed with both wide
and narrow abdominal window level settings were analyzed by two radiologists
experienced in vascular radiology. Reviewers were unaware of the clinical
outcome. Decisions were reached by consensus.
Clinical Analysis
We recorded data concerning the immediate and early clinical outcome (i.e.,
until the patient was discharged from the hospital): aortic surgery, death
before or during aortic surgery related to aortic rupture, postoperative
death, acute renal failure, acute mesenteric ischemia, and acute lower limb
ischemia. Acute renal failure was suspected in the presence of oliguria or
anuria or a serum creatinine level of twice the normal value. Mesenteric
ischemia was suspected in the presence of abdominal pain, nausea or vomiting,
and acidosis or abnormal findings on liver function tests. Acute lower limb
ischemia was suspected when the limb had absent or decreased pulses, pain,
coolness, and altered sensation. Postoperative deaths "unrelated to
aortic rupture" were recorded.
CT Analysis
We searched for two categories of signs: abnormalities of the abdominal
aorta and aorta branch lumina and low parenchymal enhancement of abdominal
organs. The presence of a compressed true lumen, defined as the bulging of the
false lumen so that the true lumen has a C-shaped configuration (Figs.
1A and
1B), was assessed. A branch
lumen, including that of the right and left renal arteries, celiac artery,
mesenteric artery, and right and left common iliac arteries, was considered to
be dissected when the branch arose from the false aortic lumen or when an
intimal flap was shown extending into the branch lumen (Figs.
1A,
1B,
1C). The number of dissected
aortic branches (i.e., renal, celiac, mesenteric, and common iliac arteries)
per patient was noted.
Low enhancement of the parenchyma in abdominal organs was considered to
exist when there was significantly less enhancement of a segment or the entire
parenchyma of a viscus in comparison with the contralateral paired viscera
(for the kidney) (Figs. 1B and
1C) or another part of the
small bowel or colic loops (Figs.
2A and
2B). Because the liver could
not be confidently analyzed at the true arterial phase and the splenic
enhancement is heterogeneous during the first minute after injection, low
enhancement in the liver and spleen was not analyzed. We used commonly
programmed narrow and wide abdominal settings (window levels, 80–300 H
and 50–500 H, respectively). The total number of low-enhanced abdominal
organs per patient was recorded.
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Fig. 2A. —63-year-old man with acute type I dissection, who presented
with clinical mesenteric ischemia. CT angiogram shows compressed aortic true
lumen, dissected mesenteric artery, normal enhancement of duodenum wall, and
low enhancement of right kidney.
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Fig. 2B. —63-year-old man with acute type I dissection, who presented
with clinical mesenteric ischemia. CT angiogram shows lack of parietal
enhancement in central small-bowel loops despite normally enhanced wall in
surrounding small bowel and colon.
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Statistical Analysis
The observed sensitivity (Se) and specificity (Sp) of CT findings,
including abnormalities of the aorta and branches of the aorta and a low
enhancement of the parenchyma in abdominal organs to predict post-operative
death, were calculated as Se = true-positive / true-positive +
false-negative and Sp = true-negative / true-negative +
false-positive. The 95% confidence interval (CI) was calculated according to
the Exact method. A correlation between the number of dissected arteries or
low-enhanced abdominal organs and the postoperative death rate was sought
using a binary logistic regression.
Results
Patient Outcome
Postoperative deaths are presented in
Table 1. Almost as many
patients died of ischemic complications (n = 11) as from aortic
rupture (n = 12 [patients excluded from data]). Among the 48
patients, postoperative death occurred in four of five patients with clinical
mesenteric ischemia, eight of 18 patients with clinical acute renal failure,
and six of six patients with clinical lower limb ischemia.
Two of the five patients with mesenteric ischemia underwent laparotomy
without bowel resection because advanced stages of ischemia were found. Five
of the 18 patients with acute renal failure underwent dialysis. Three of the
six patients with lower limb ischemia underwent surgery (a second intervention
with femorofemoral by-pass performed in two patients with type I dissection
and extensive débridement of the muscular compartment with ischemic
edema in one patient with type III dissection and long-lasting limb
ischemia).
Among the six patients with type III dissection, two underwent successful
surgical repair of aortic rupture, two underwent successful surgical repair of
retrograde dissections involving the aortic arch, one nonsurgical patient had
a favorable clinical outcome despite a splenic infarction and pancreatitis.
One nonsurgical patient died from profound limb ischemia complicated by renal
failure, metabolic abnormalities, end-organ failure, threatened loss of limb,
and neurologic weakness.
Dissected Aortic Branches on CT and Postoperative Deaths
CT findings for the aorta and peripheral branch vessels are presented in
Tables 2 and
3. The number of postoperative
deaths did not correlate with the number of dissected peripheral branch
vessels (p = 0.17) (Table
3). CT depicting one or two dissected renal arteries was 37.5%
sensitive (95% CI, 4–71%) and 86% specific (95% CI, 74.8–97.2%)
for postoperative death. CT depicting a dissected mesenteric artery was 18.2%
sensitive (95% CI, 2.3–51.8%) and 83.8% specific (95% CI,
68.0–93.8%) for postoperative death. CT depicting one or two dissected
common iliac arteries was 63.6% sensitive (95% CI, 30.8–89.1%) and 62.2%
specific (95% CI, 44.8–75.5%) for postoperative death. Nineteen
patients, all with type I dissections, had a dissected subclavian or carotid
artery. Three of them developed a permanent (n = 2) or transient
(n = 1) neurologic deficit. None of the patients with a dissected
subclavian or carotid artery died.
Compressed Aortic True Lumen and Postoperative Death
CT depicting a compressed aortic true lumen was 63.6% sensitive (95% CI,
30.8–89.1%) and 78.4% specific (95% CI, 61.8–90.2%) for
postoperative death.
Low Enhancement of Parenchyma in Abdominal Organs and Postoperative Death
CT findings of low enhancement of parenchyma in organs are presented in
Tables 4 and
5. The number of postoperative
deaths correlated with the number of low-enhanced abdominal organs (p
< 0.00005). Death occurred in one of five patients with low enhancement in
one abdominal organ (digestive tract or kidneys) and in seven of eight
patients with low enhancement of parenchyma in two abdominal organs
(Table 5). All patients with
bilateral renal low enhancement and three of the four patients with low
enhancement of the small bowel or colic loops had fatal outcomes. CT depicting
low enhancement in one or two kidneys was 54.5% sensitive (95% CI,
23.4–83.3%) and 91.9% specific (95% CI, 78.1–98.3%) for
postoperative death. CT depicting low enhancement in the small bowel or colic
loops was 27.3% sensitive (95% CI, 6.0–61.0%) and 97.3% specific (95%
CI, 85.8–99.9%) for postoperative death.
Discussion
This study emphasizes the potential of CT findings depicting a low
enhancement of parenchyma in abdominal organs to predict a patient's death.
Our results show that the postoperative death rate depends on the number of
abdominal organs with low enhancement of parenchyma and not on the number of
dissected aortic branch vessels.
Emergency surgical repair is the rule when the ascending aorta has an acute
dissection. The Stanford classification
[12] distinguishes between
type A, when the dissection involves the ascending aorta, and type B, when the
dissection does not involve the ascending aorta. As a result, it is the most
commonly used classification to manage acute aortic dissection. The De Bakey
classification subdivides the dissection process further: a type I dissection
involves the entire aorta, a type II dissection involves the ascending aorta,
and a type III dissection involves the descending aorta
[11]. Because this
classification is most suitable for identifying patients at risk for abdominal
aortic dissection (i.e., types I and III), it was used in this study instead
of the commonly used Stanford classification.
Malperfusion is clinically defined as a complication in an organ system
associated with ischemia and resulting in organ dysfunction and systemic
metabolic abnormalities [7].
This dreaded complication of aortic dissection is ultimately responsible for
the 51–60% death rate, despite successful surgical repair of the aorta
[1–3,
13]. Routinely, treatment is
undertaken in patients showing clinical signs of ischemia
[5]. This practice could
explain the high rate of death reported in the literature and in our study in
cases of malperfusion because clinical and biologic signs of ischemic
complications are delayed. Moreover, endovascular therapeutic management of
ischemic complication
[14–18]
was not yet performed in our institution during the study period.
To predict malperfusion using a commonly available imaging technique is the
current challenge for the radiologist. Because the postoperative death rate
increases when the number of abdominal organs with low enhancement of
parenchyma increases and malperfusion is the most commonly reported cause for
postoperative deaths during acute aortic dissection, our hypothesis is that
malperfusion could be the physiopathologic explanation for the low enhancement
of parenchyma in abdominal organs.
Mechanisms responsible for branch vessel compromise with ischemia during
aortic dissection are now classified as static when the dissection intersects
and narrows the vessel origin or as dynamic when the dissection spares the
vessel origin but the dissection flap appears to compress the aortic true
lumen at or above the origin or covers the origin of the aortic branch vessel.
Both mechanisms may be simultaneously present
[19]. However, our study shows
that the most relevant sign to predict postoperative death is extensive number
of abdominal organs with low enhancement of parenchyma, and such information
should be communicated to the surgeon before any therapeutic intervention.
The recently reported 96% sensitivity of helical CT to depict mesenteric
ischemia of the small bowel and colic loops
[20,
21] emphasizes the potential
usefulness of CT to reveal mesenteric ischemia in aortic dissection.
Unfortunately, CT signs of renal malperfusion have limitations. First, CT
cannot depict diffuse and subtle bilateral abnormalities of the renal
parenchyma. Second, CT was performed early, always before performing aortic
surgery. Indeed, acute renal failure, worsened by long-standing or delayed
decreased perfusion and operative shock, was generally not present at the time
of CT. As previously shown, the explanation for the lower enhancement of the
kidney during the perfusion phase is a difference in false-lumen and
true-lumen transit time [22,
23].
CT performed immediately after surgical aortic repair should also be
specific for predicting postoperative death because improvements of visceral
perfusion could be expected by closing the main aortic tear on the ascending
aorta. Unfortunately, our study does not support this hypothesis because CT
was always performed before aortic surgery. Further studies, including both CT
evaluation of low-enhanced abdominal organs and clinical follow-up of patients
specifically treated for suspected ischemic complications, are needed to
assess whether low enhancement of parenchyma in abdominal organs occurs early
enough to correspond to clinically reversible ischemia. This is especially
important for mesenteric ischemia.
The most controversial point is the effect of the CT technique on the
intensity of organ enhancement
[24]. In our study, the delay
between injection and acquisition was always less than 60 sec. Then, we always
observed the first perfusion phase, which is responsible for the cortical
nephrogram. In case of a very short delay and fast acquisition, for example
using MDCT, the technique may strongly influence the CT findings in aortic
dissections. Whether it would increase or decrease the CT sensitivity and
specificity to depict malperfusion is unknown. As a control of quality, at
least one organ or one segment of an organ should have a correct enhancement
to allow sufficient confidence when comparing the parenchymal enhancement of
another organ with the organ being scanned. CT is becoming the first-choice
imaging technique for investigating aortic dissection
[25,
26] because it is available in
an emergency, explores the entire aorta and its branches, and helps identify
extraaortic diseases in patients with thoracoabdominal symptoms. Because a low
enhancement of parenchyma in abdominal organs on CT can help identify patients
at risk of postoperative death in acute aortic dissection, low-enhanced
abdominal organs in a case of aortic dissection should be systematically
reported before surgery is initiated.
Acknowledgments
We thank Guillaume Gautier for assistance in preparing the manuscript.
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Abstract
Introduction
