ABDOMINAL AORTIC ANEURYSM
Left panel shows Krakatoa before the eruption, London Illustrated News, 1883. Right panel shows a
recent photograph of Anak Krakotoa, (the “child of Krakatoa”)
“I blinked hard, looked again. I measured it as best I could against the big peak to the left, trying to
recall where the smaller mountain had stood in relation to that cliff wall. It was higher up now surely.
Yes, there was no doubt. Memory does play tricks in situations like this, to be sure: but as I stared long
and hard, I became ever more certain. The volcano, the child of Krakatoa had grown very much
larger during the 25 years I had been away. When I got back to the maps, I checked and could see in
short order that the modern surveys all agreed. The small island-mountain, which had been born out
of the sea 40 odd years after the very explosion that destroyed and vaporized its parent, was now itself
growing fast, thrusting upwards at an extraordinary rate. By looking at the old charts and maps that
had been published down the years since the last week of June 1927, when it was first seen above the
waves, it was possible to calculate…it was fully five hundred feet taller than when I had last seen it!”
So wrote Simon Winchester in his best selling book “Krakatoa”, 2003. On the 27th of August 1883 the
original Island of Krakatoa erupted with the awesome force of nature, dwarfing anything mankind has
achieved with nuclear detonations. The impact was truly global, destroying the island itself, killing
40,000 people on neighboring Java with the tsunami it generated and sending immense rafts of pumice
floating toward Africa. The sound of the explosion was heard up to one thousand miles away and
barographs around the world showed the shock wave encircled the globe seven times over. Ash in the
upper atmosphere lingered for two years, producing stunning sunsets as far away as London and New
York. It is little wonder the citizens of Java today observe the ever expanding Anak Krakatoa with a
sense of foreboding.
When an abdominal aortic aneurysm is detected in our patients we must be ever vigilant, like the
Javanese watching over Anak Krakatoa, in observing its size and rate of expansion. When an
aneurysm reaches five centimeters, surgical intervention, like emigration for the Javanese, should be
seriously considered before it “erupts”.
ABDOMINAL AORTIC ANEURYSM
Introduction
Abdominal aortic aneurysm, (AAA) may present to the Emergency Department in a variety of ways
including:
●
An incidental finding.
●
An acute expansion of the aneurysm
●
A contained leak
●
A shocked patient as a result of frank rupture.
●
An atypical presentation
Pathophysiology
Terminology
By strict definitions an aneurysm is a permanent localized or diffuse dilation of an artery at least 1.5
times its normal diameter and involving all three layers of the vessel wall.
The term “ectasia” is used when the dilation is less than 50 %.
Aneurysms are commonly described as fusiform if the entire circumference of the vessel wall is
dilated and saccular if only part of the circumference is involved.
False aneurysms (or pseudoaneurysms) are a localized collection of flowing blood that communicates
with the arterial lumen, but is contained only by the adventitia.
Epidemiology
AAA is rare before the age of 50 years.
Thereafter the incidence rises with age. Up to 10 % of elderly males aged between 65-79 years will
develop an abdominal aneurysm.
Pathology
Aneurysms are due to:
1.
Degenerative changes in connective collagen and elastin tissues that occur with age
2.
Atherosclerotic vascular disease.
Rare causes include:
3.
Infective, (mycotic, syphilitic)
4.
Post trauma
5.
Post aortic dissection
6.
Inflammatory artertitis, (ie rheumatic diseases such as PAN)
7.
Genetic factors:
●
There is an approximately 15 % incidence of aneurysms amoung first degree relatives
of patients with aortic aneurysms
●
Inherited genetic disorders: (Marfan’s syndrome, Ehlers-Danlos syndrome).
Location
Most abdominal aortic aneurysms occur in the infra-renal segment, (90-95%)
While it is uncommon for AAAs to extend above the renal arteries, extension into the iliac arteries is
common.
Clinical features
Incidentally detected aneurysms:
AAA may be detected in the ED as an incidental finding, either clinically or by ultrasound or by
radiological means.
Clinically detectable abdominal aneurysm:
●
Note that in thin patients, arterial pulsation from the abdominal aorta may be detected in the
epigastrium normally. This will be felt as a pulsation in the AP direction.
●
To help determine whether this actually represents an aneurysm (as opposed to normal arterial
pulsations), it must be determined whether the pulsation is “expansile” (ie enlarges appreciably
with systole).
This is best done by aligning two fingers on either side of the pulsating mass and looking for
appreciable separation of the fingers with each pulsation. 1
Abdominal aortic aneurysms generally become clinically detectable at approximately 4–5 cm,
however this will also depend largely on body habitus.
An acute expansion of the aneurysm
Patients with known AAAs may present to the Emergency Department with acute onset of back pain,
or simply epigastrc pain.
Although the aneurysm has not overtly ruptured, or even ruptured with a small retroperitoneal bleed,
these symptoms may still relate to a AAA, due to an acute expansion.
A contained leak
A rupture may occur but the leak of blood may be contained within the retroperitoneal space and so
the patient may appear to be relatively hemodynamically stable - although alternatively they mat not
be!
Pain will usually be significant and will more commonly be located in the back, rather than in the
region of the epigastrium
A shocked patient as a result of frank rupture
This is the most dramatic presentation of a AAA.
The bleed may be confined to the retroperitoneal space, or it may have ruptured into the peritoneal
space
The “classically” described clinical triad is:
1.
Pain, typically severe and predominantly located in the back
2.
Signs of circulatory compromise/ hypovolemic shock.
3.
The presence of a pulsatile mass in the abdomen
Note however that this clinical sign may be difficult to elicit, (or not elicited at all) particularly
in the following situations:
●
Hypotensive patients
●
Obese patients
●
In presence of large retro peritoneal hematomas
●
Patients with excessive voluntary guarding of abdominal muscles
Atypical Presentations of Aortic Aneurysms
There are a number of well recognized atypical presentations of AAA.
Important examples include:
1.
Elderly with back pain:
●
2.
Remember that renal colic is unusual in the elderly (and not all back pain in the elderly
is “arthritis”).
Elderly with acute severe back pain with radiation to the legs:
●
3.
Chronic severe back pain in elderly:
●
4.
This may in fact be due to a chronic contained rupture, even if the patient is “stable”.
Patients with known AAA who develop tenderness to the aneurysm on palpation:
●
5.
This may not be “sciatica”, as an expanding AAA may cause pressure on
retroperitoneal nerve roots.
This must be assumed to be due to the aneurysm in the first instance. It can represent an
acute expansion or a small contained leak.
Massive GIT bleeding in a patient with a AAA:
●
This may be the result of an aorto-enteric fistula, most often in the setting of a previous
AAA graft that has expanded and eroded into the GIT.
●
This condition must always be borne in mind in any patient with a GIT bleed who has
had a previous AAA repair.
●
CT scan with contrast will diagnose this condition.
●
If found, immediate operative repair is indicated.
Investigations
Blood tests
1.
FBE
2.
U&Es/ glucose
3.
Blood group:
●
4.
Group and hold, or cross match, as clinically indicated.
Coagulation profile.
Plain radiography
Plain radiography cannot make a definitive diagnosis of aortic rupture.
It can only give indirect clues to the presence of an abdominal aortic aneurysm and a normal plain xray does not exclude the presence of a AAA.
Plain AXR radiological findings include:
●
Mural calcification of the aneurysm wall may be seen on AXR.
●
On the AP the left margin of the aneurysm is usually distinguished. The right border is
generally obscured by the vertebral column.
●
For this reason a lateral projection is often more useful were the full extent of the aneurysm
may be better appreciated as it is projected away from the spine.
ECG
This is routinely done in any unwell patient, however in the patient who is shocked with a suspected
ruptured AAA, this should never delay definitive investigations and / or management
Ultrasound
Ultrasound is an excellent first up investigation that can be done in the ED, to confirm the
presence of an AAA.
It is the best also investigation in the unstable patient as it can be done in the resus cube.
It can detect an aneurysm as well as free fluid, however it cannot definitively determine that the fluid is
from a ruptured aneurysm. Although the information obtained from it, together with the clinical setting
may be enough to enable a vascular surgeon to operate in cases of suspected free rupture.
Conventional measurement of the size of AAAs is the maximum AP diameter in the transverse plane.
Ultrasonic appearance of an 8 cm aneurysm as measured in the A-P direction, transverse plane.
Two ultrasonic views of a AAA, left in transverse view, and right in longitudinal view, (from
Ultrasound in Emergency Medicine Course Handbook, March 2004, Australian Institute of
Ultrasound, with permission).
CT Scan
CT with contrast is the best investigation, as it will reliably show the size and extent of an
aneurysm and is able to demonstrate the leakage of blood from it. It can also delineate any other
associated complications of the aneurysm.
In some situations patients will have significant renal impairment which will put them at risk of
acute renal failure if contrast is given. In these cases the situation should be discussed with the
vascular surgeon. A non-contrast scan may be sufficient to provide enough information to make
the diagnosis and allow the vascular surgeon to operate.
The investigation may be problematic in the unstable patient, however patient “stability” or otherwise
should not dictate whether or not the investigation should be done, as is sometimes claimed. It all
depends on the degree of certainty of diagnosis. In real life this is sometimes not quite a clear cut as
many textbooks would have one believe.
If the clinical picture is clear enough, and backed up by ultrasound findings, then CT scan is not
necessary in the unstable patient as the vascular surgeon will have enough information to operate.
Delays in obtaining an unnecessary CT scan to confirm the diagnosis in these situations can be
detrimental to the patient.
If the patient is relatively unstable and the diagnosis is uncertain, on both clinical and ultrasound
examination, then a diagnosis still needs to be established and the patient must have the CT scan to
confirm it, regardless of “stability”, (unless an individual surgeon is prepared to do a laparotomy
without diagnosis) - each case has to be assessed on its merits, rather than work to a formula.
Of course preliminary emergent resuscitation must be undertaken to point at least enough to get the
patient to the scanner. All resuscitation equipment, monitoring equipment and appropriately trained
staff should accompany the patient to the scanner, in anticipation of possible further deterioration.
MRI
This is highly accurate in defining aneurysms in elective situations.
The investigation however is not generally suitable for evaluation of cases of suspected rupture, due to
long scan times, limited availability, and inability of distressed patients to cooperate for the
examination.
Management
Of incidental findings of aneurysms
All incidentally found aortic aneurysms should be referred to a vascular surgeon review, if the patient
is a potential candidate for surgery.
The urgency of follow-up will depend on the size of the aneurysm and whether or not there are
symptoms associated with it.
In general terms:
< 2 cm is within normal limits.
2-5 cm and without symptoms, will need to be followed with regular ultrasounds
> 5 cm will require operation in suitable candidates, even in the absence of symptoms.
AAA of > 6 cm at diagnosis has a 5 year survival rate of only 20 % and about 50 % will rupture
within one year of diagnosis.
Note however that even though the risk of rupture increases with its size, there is no real “safe” size
for an aneurysm, and it is impossible to predict when an individual aneurysm will rupture.
The mortality rate of AAA can be lowered by elective repair before rupture occurs.
The decision to operate will be based on:
●
Size of the aneurysm
●
Growth rate of the aneurysm
●
Symptoms
●
Patient suability for surgery ( ie age and co0morbidity factors)and wishes.
An acute expansion of the aneurysm
Any aneurysm that is causing symptoms should be considered an emergency, even if it has not
ruptured and the patient is stable.
The pain could be due to an acute expansion of the aneurysm.
All cases should be referred to the vascular surgical unit.
A contained leak
When detected, these should be repaired urgently; however the time frame may not be so acute as in
cases of free rupture
A shocked patient as a result of frank rupture.
1.
ABC measures, as required.
2.
Two large bore IV peripheral cannulae both with “pump” sets.
3.
Fluids to a systolic pressure of around 90 mmHg is sufficient:
●
4.
5.
The priority, however is not total fluid resuscitation, but definitive surgical
intervention!
Urgent blood cross matching:
●
FBE/ U&Es / glucose/ coagulation profile.
●
Cross match 6 units of blood, (up to 10 even more however may be required).
Monitoring:
If the patient is stable:
6.
●
ECG continuous monitoring
●
Arterial line (only if this is not delaying time to investigation and theater)
●
Urinary catheter is not essential in first instance, this can be placed later in theater
●
CVC is not essential in first instance, this can be placed later in theater
Analgesia:
●
7.
Titrate IV opioid analgesia as required
Urgently notify the following:
●
The vascular surgical unit.
If there is clinical suspicion of a ruptured abdominal aortic aneurysm, this should be
conveyed to the vascular surgical unit even before imaging, to maximize the ability for
planning and organization of timely intervention.
8.
●
The Intensive Care Unit
●
Anesthetist/ operating theater
●
Blood bank for urgent blood and the possible need for FFP and platelets.
Surgical Options of Repair
Ruptured AAA is uniformly fatal unless treated surgically.
There are two treatment options:
Endovascular stent grafting:
●
This is much less invasive than open repair and has less mortality.
●
It is the preferred method in unruptured AAAs where possible
●
It selected cases it can also be utilized in ruptured AAAs.
Open repair:
●
This is undertaken for cases that are not amenable to endovascular stenting.
●
The accepted mortality rate for elective repairs is less than 5 %.
●
Of those that survive to hospital with a ruptured AAA, mortality for open surgical
repair is still high.
●
Mortality will be closely related to age, co-morbidities, and degree of shock.
Appendix 1
Axial and reconstructed images of an abdominal aortic aneurysm. There is also a right iliac artery
aneurysm which is partially occluded by thrombus. 3
Radiographic appearance of an intravascular stent within the distal aorta and proximal common iliac
vessels bilaterally in a 72 year old male.
References:
1.
Talley NJ, O’Conner S, Clinical Examination, 3rd Ed 1996, p.170.
2.
Chung C. H. Aneurysms, in “Adult Textbook of Emergency Medicine”, Cameron et al. 3rd ed
2009.
3.
Diagnostic Imaging Pathways: www.imagingpathways.health.wa.gov.au/
Dr James Hayes
Reviewed 25 May 2011.