Abdominal aortic aneurysm (AAA) rupture is a feared complication of abdominal aortic aneurysm and is a surgical emergency. It is part of the acute aortic syndrome spectrum.
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Epidemiology
Abdominal aortic aneurysms are common and affect ~7.5% of patients aged over 65 years 6.
The risk of rupture is related to the size of the AAA. One study suggested that the 1-year risk of AAA rupture based on the initial diameter is 10:
9% at 5.5-5.9 cm
10% at 6.0-6.4 cm
19% at 6.5-6.9 cm
33% at ≥7.0 cm
26% of AAA reaching 8 cm rupture within 6 months 10.
Clinical presentation
The classical triad of pain, hypotension, and pulsatile abdominal mass due to rupture into the retroperitoneum is only seen in 25-50% of patients.
A chronic rupture may go undetected for weeks to months, and is known as a sealed aneurysmal rupture, spontaneously healed aneurysmal rupture, or abdominal aortic aneurysmal leak.
Unusual presentations of a ruptured AAA include:
transient lower limb paralysis
right upper quadrant pain
groin pain
testicular pain
testicular ecchymosis (blue scrotum sign of Bryant)
Pathology
The aneurysmal rupture is thought to occur when the mechanical stress is in excess of the wall strength. Thus, the aortic aneurysmal wall tension and the aneurysmal diameter are a significant predictor of impending rupture.
The commonest sites of rupture by relative incidence are:
retroperitoneal: 80%
intraperitoneal: 20%
aortocaval fistula: 3-4%
primary aortoenteric fistula: <1%
aorto-left renal vein fistula: very rare; <30 cases reported
Radiographic features
Plain radiograph
Abdominal radiographs are not a sensitive mode of detection. A calcified aortic aneurysm may be seen with a secondary blurring of the psoas outline in case of retroperitoneal hemorrhage.
Ultrasound
Not used for routine diagnosis but reported features include:
focal dilatation of the aorta (aneurysm)
focal defect at the interface between the vessel lumen and intraluminal thrombus
sharply demarcated aortic mural defect
partially detached, mobile layer of intraluminal thrombus 7
hypoechoic para-aortic fluid collection 8
free intraperitoneal fluid
-
heterogeneous collection within a retroperitoneal space
represents retroperitoneal hemorrhage
CT / CT angiography
Retroperitoneal hemorrhage adjacent to the aneurysm is the most common finding. The periaortic blood may be seen to extend into perirenal or pararenal spaces or the psoas muscles. Intraperitoneal extension of the hemorrhage may be seen as an immediate or delayed finding.
An important feature seen in contained rupture of an aortic aneurysm is the draped aorta sign - in which the posterior wall of the aorta is not seen distinctly from adjacent structures, and the contour of the aorta follows that of adjacent vertebrae.
A high-attenuation crescent sign, which is an area of increased attenuation within the aortic aneurysmal mural thrombus, can be demonstrated on plain CT images. This is caused by the insinuation of fresh blood into the mural thrombus and aortic wall.
In post-contrast studies or CT angiography, active extravasation of contrast material can be seen.
Findings predictive of impending rupture
increased aneurysm size on serial imaging (rate of 10 mm or more per year)
very large abdominal aortic aneurysm >7 cm
reduced thrombus size
discontinuity in calcification
-
high-attenuation crescent sign
well-defined peripheral crescent of increased attenuation within the thrombus of a large abdominal aortic aneurysm 9
Treatment and prognosis
Treatment of an acute rupture should be prompt and can be with endovascular aneurysm repair (EVAR) or open surgery. The mortality rate is very high being >90% 6.
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