DOI:10.2214/AJR.05.1554
AJR 2007; 188:W57-W62
© American Roentgen Ray Society
CT Findings of Rupture, Impending Rupture, and Contained Rupture of Abdominal Aortic Aneurysms
Stephanie A. Schwartz1,
Mihra S. Taljanovic1,
Stephen Smyth1,
Michael J. O'Brien1 and
Lee F. Rogers1
1 All authors: Department of Radiology, The University of Arizona Health
Sciences Center, 1501 N Campbell Ave., PO Box 245067, Tucson, AZ
85724-5067.
Received September 1, 2005;
accepted after revision October 10, 2005.
Address correspondence to S. A. Schwartz
(schwartz{at}radiology.arizona.edu).
WEB
This is a Web exclusive article.
Abstract
OBJECTIVE. With the increasing use of cross-sectional imaging for a
variety of medical and surgical conditions affecting the abdomen and pelvis,
familiarity with the imaging features of aneurysm rupture—and the
findings suspicious for impending or contained aneurysm rupture—is
crucial for all radiologists. This pictorial essay will review the imaging
findings of rupture of abdominal aortic aneurysms and of complicated
aneurysms.
CONCLUSION. Prompt detection of abdominal aortic aneurysm rupture or
impending rupture is critical because emergent surgery may be required and
patient survival may be at stake.
Keywords: abdominal aortic aneurysm • aorta • CT angiography • MRI
Introduction
Abdominal aortic aneurysm rupture is the 13th leading cause of death in the
United States [1]. The classic
clinical triad of aneurysm rupture is present in up to 50% of patients and
includes abdominal pain, pulsatile abdominal mass, and shock
[2].
The risk of abdominal aortic aneurysm rupture relates to the maximum
cross-sectional diameter of the aneurysm
[1]. For aneurysms less than 4
cm in diameter, a 6-year cumulative incidence of rupture of 1% has been
reported [2]. The risk of
rupture for 4- to 5-cm aneurysms is estimated to be 1-3% per year, increasing
to 6-11% per year for 5- to 7-cm aneurysms. Aneurysms with a cross-sectional
diameter greater than 7 cm have a risk of rupture approximating 20% per year
[1].
Rupture most commonly involves the posterolateral aorta with hemorrhage
into the retroperitoneum (Figs.
1A,
1B,
1C,
1D,
1E,
1F,
1G, and
1H). Intraperitoneal rupture
may also occur, originating from the anterior or anterolateral aspect of the
aneurysm [2].
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Fig. 1A —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. Axial T1- and T2-weighted MR images show large right
retroperitoneal hematoma containing flow void (arrows).
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Fig. 1B —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. Axial T1- and T2-weighted MR images show large right
retroperitoneal hematoma containing flow void (arrows).
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Fig. 1C —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. Contiguous axial CT angiograms obtained immediately
after MRI reveal large right retroperitoneal hematoma with contrast
extravasation from posterolateral aorta (arrows, C and
E). Operatively, large right retroperitoneal hematoma was seen, and
pathologic evaluation revealed area of aortic wall discontinuity and
associated organized hematoma.
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Fig. 1D —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. Contiguous axial CT angiograms obtained immediately
after MRI reveal large right retroperitoneal hematoma with contrast
extravasation from posterolateral aorta (arrows, C and
E). Operatively, large right retroperitoneal hematoma was seen, and
pathologic evaluation revealed area of aortic wall discontinuity and
associated organized hematoma.
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Fig. 1E —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. Contiguous axial CT angiograms obtained immediately
after MRI reveal large right retroperitoneal hematoma with contrast
extravasation from posterolateral aorta (arrows, C and
E). Operatively, large right retroperitoneal hematoma was seen, and
pathologic evaluation revealed area of aortic wall discontinuity and
associated organized hematoma.
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Fig. 1F —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. CT angiograms obtained 3 months before MRI show
irregular contour of posterolateral aorta (arrows, G) with
surrounding soft-tissue density (arrows, H), compatible with
unrecognized contained rupture.
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Fig. 1G —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. CT angiograms obtained 3 months before MRI show
irregular contour of posterolateral aorta (arrows, G) with
surrounding soft-tissue density (arrows, H), compatible with
unrecognized contained rupture.
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Fig. 1H —67-year-old man with known abdominal aortic aneurysm who had
3-month history of lower back and right groin pain. Patient underwent MRI of
lumbar spine and pelvis. CT angiograms obtained 3 months before MRI show
irregular contour of posterolateral aorta (arrows, G) with
surrounding soft-tissue density (arrows, H), compatible with
unrecognized contained rupture.
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Abdominal aortic aneurysm rupture into the bowel usually involves the
duodenum and is uncommon. Death due to exsanguination is the usual result, but
slow leaks may present with melena and mimic peptic ulcer disease
[2].
Rupture into the inferior vena cava is rare (Figs.
2A,
2B, and
2C). The clinical presentation
of acute aortocaval fistula usually includes high-output cardiac failure,
lower extremity swelling, and engorged veins
[2].
Although the imaging findings of abdominal aortic aneurysm rupture are
usually obvious, small ruptures can be mistaken for unopacified bowel, lymph
node enlargement, or perianeurysmal fibrosis. Careful examination of the
morphology of the aneurysm may aid in detecting subtle ruptures.
In a retrospective study, Siegel et al.
[3] evaluated CT scans of
patients with ruptured and nonruptured abdominal aortic aneurysms to determine
whether a number of morphologic features were associated with rupture. The
length of the aneurysm was not significantly different between the rupture and
control groups. The ruptured aneurysms had significantly larger
anteroposterior and transverse dimensions. The two groups had similar rates of
lumen irregularity. Ruptured aneurysms contained a lesser amount of thrombus
than aneurysms that were not ruptured. Thrombus calcification was seen more
commonly in nonruptured aneurysms, which was thought to be related to the
greater amount of thrombus in the nonruptured aneurysms.
Attenuation characteristics of the thrombus that were not associated with
rupture included the homogeneous, diffusely heterogeneous, and low-attenuation
periluminal halo patterns [3].
High-attenuation crescents within the mural thrombus were seen only in
ruptured aneurysms in the study by Siegel et al
[3]. Mural calcification
patterns were also evaluated, and a focal discontinuity in otherwise
circumferential calcification was rare and seen only in ruptured aneurysms. It
was noted, however, that mural calcification was often discontinuous, and the
discontinuity was most useful when shown to be new compared with a prior scan
[3].
Hyperattenuating Crescents: A Sign of Impending Rupture
Pillari et al. [4] described
the concept of thrombus transformation with contrast extravasation into the
thrombus and lumen irregularity as findings that may signify impending
rupture. High-attenuating crescents in the wall of abdominal aortic aneurysms
on unenhanced CT scans were initially described as a sign of impending rupture
by Mehard et al. [5] (Figs.
3A,
3B,
3C,
4A, and
4B). In that retrospective
study, the high-attenuating crescents were present in 77% of patients with
complicated aneurysms, with complications including intramural hematoma,
contained rupture, and frank rupture. The specificity of the
"high-attenuating crescent" sign was 93%.
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Fig. 3A —87-year-old man with 12-hour history of severe back pain.
Enhanced axial CT images reveal 7 x 9 cm abdominal aortic aneurysm with
high-attenuation crescents within mural thrombus (thick arrows,
A and B) and minimal periaortic stranding (thin arrows,
C). Contained rupture was present at surgery.
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Fig. 3B —87-year-old man with 12-hour history of severe back pain.
Enhanced axial CT images reveal 7 x 9 cm abdominal aortic aneurysm with
high-attenuation crescents within mural thrombus (thick arrows,
A and B) and minimal periaortic stranding (thin arrows,
C). Contained rupture was present at surgery.
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Fig. 3C —87-year-old man with 12-hour history of severe back pain.
Enhanced axial CT images reveal 7 x 9 cm abdominal aortic aneurysm with
high-attenuation crescents within mural thrombus (thick arrows,
A and B) and minimal periaortic stranding (thin arrows,
C). Contained rupture was present at surgery.
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Fig. 4A —87-year-old man with known aneurysm and back pain. Axial
enhanced CT image shows 7-cm abdominal aortic aneurysm with faint crescentic
area of increased attenuation within mural thrombus (arrows). Patient
was not surgical candidate due to comorbid conditions.
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Fig. 4B —87-year-old man with known aneurysm and back pain. Enhanced
CT image obtained 3 months after A shows anterior aneurysm rupture
(black arrow) with associated retroperitoneal hemorrhage (white
arrows).
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For a crescent to be considered high attenuation by Siegel et al.
[3], the crescent needed to be
well defined and of higher attenuation than the psoas muscle on enhanced scans
or of higher attenuation than that of the patent lumen on unenhanced scans. In
that study, crescents of increased attenuation were present in 21% of ruptured
aneurysms and in none of the patients with intact aneurysms.
Hyperattenuating crescents have been attributed histopathologically to
hemorrhage into the mural thrombus or into the aneurysm wall, with clefts of
blood seeping from the lumen into the thrombus. The hemorrhage later
penetrates the aneurysm wall, which weakens the wall. This places the aneurysm
at risk for frank rupture, and prompt surgical consultation should be obtained
[6].
Chronic Contained Rupture
Several reports in the literature have described abdominal aortic aneurysms
associated with retroperitoneal hemorrhage in patients who are hemodynamically
stable. The reported cases have variable histories of back pain or clinical
symptoms atypical for aneurysm rupture including obstructive jaundice, femoral
neuropathy, and symptomatic inguinal hernia. The duration and severity of
symptoms, and the hemodynamic status of the patient, are used to differentiate
acute from chronic rupture [7].
According to Jones et al. [7],
chronic contained ruptures should meet the following criteria: known abdominal
aortic aneurysm, previous pain symptoms that may have resolved, stable
hemodynamic status with a normal hematocrit, CT scans showing retroperitoneal
hemorrhage, and pathologic confirmation of organized hematoma (Figs.
1A,
1B,
1C,
1D,
1E,
1F,
1G, and
1H).
Draping of the posterior aspect of the aorta over the adjacent vertebral
body is an indicator of aortic wall insufficiency and contained rupture, even
in the absence of retroperitoneal hemorrhage (Figs.
5A,
5B,
6A, and
6B). Associated vertebral body
erosion may be seen [8].
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Fig. 5A —Elderly man with 3-day history of back pain. Enhanced CT
images show 5-cm abdominal aortic aneurysm with draping of posterior wall over
vertebral body (arrows). Contained rupture was found at surgery, with
vertebral body visible through aortic lumen.
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Fig. 5B —Elderly man with 3-day history of back pain. Enhanced CT
images show 5-cm abdominal aortic aneurysm with draping of posterior wall over
vertebral body (arrows). Contained rupture was found at surgery, with
vertebral body visible through aortic lumen.
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Fig. 6A —Elderly man with abdominal pain. Enhanced CT images show 5-cm
abdominal aortic aneurysm with irregular posterior aortic contour and draping
of aorta over vertebral body (arrows). Patient suffered cardiac
arrest shortly after CT. Autopsy revealed pneumonia as cause of death, but
aortic wall was paper thin and adherent to vertebral body.
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Fig. 6B —Elderly man with abdominal pain. Enhanced CT images show 5-cm
abdominal aortic aneurysm with irregular posterior aortic contour and draping
of aorta over vertebral body (arrows). Patient suffered cardiac
arrest shortly after CT. Autopsy revealed pneumonia as cause of death, but
aortic wall was paper thin and adherent to vertebral body.
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Differentiation of contained rupture from frank rupture of abdominal aortic
aneurysms is vital in selecting proper treatment. Stable patients may benefit
from preoperative assessment and management. Emergent surgery for aneurysms in
stable patients carries an increased mortality rate, whereas urgent repair has
mortality rates comparable to those of elective surgery
[7].
Conclusion
Prompt detection of abdominal aortic aneurysm rupture is critical because
survival is improved by emergent surgery. Identification of impending or
contained rupture is equally important because these patients are at risk for
frank rupture but can generally benefit from a more thorough preoperative
assessment, followed by urgent surgery.
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Abstract
Introduction
