Anthony J. Dean, M.D. and Bon S. Ku, M.D.
I. Introduction and Indications
A ruptured abdominal aortic aneurysm (AAA) is a vascular catastrophe responsible
for 1-3% of deaths in men from the age 65-85 in developed countries. (1) AAA
is the 13th leading cause of death in the United States, causing about
15,000, or 0.8% of all deaths annually. (2,3) Rupture
from an AAA is the 10th leading cause of death in males over 50 and the
incidence of AAA continues to increase.(1) Currently,
the U.S. Preventative Services Task Force recommends that men from the
age of 65-75 years who have ever smoked be screened once for an AAA by
The lethality of a ruptured AAA is devastating; the mortality rate after rupture approaches 90%. (3) Therefore, it is essential for the emergency medicine physician to recognize the presence of an AAA in an expeditious manner. A patient who presents with a ruptured AAA will usually not have the classic triad of hypotension, back pain, and a pulsatile abdominal mass. Wrong diagnoses such as gastrointestinal bleed, nephrolithiasis, and diverticulitis are often made. Delayed diagnosis can obviously prove detrimental to the patient with a symptomatic AAA.
The physical exam is often unreliable in detecting the presence of an AAA and should never be used to rule it out. Abdominal palpation has been shown to have a moderate sensitivity of 68% in diagnosing an AAA. (5) Other modalities for detecting an AAA include conventional radiography, ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), and arteriography. Ultrasound, utilized since the 1980’s to inspect the abdominal aorta, is an ideal method for detecting AAA’s due to its accuracy combined with low cost, rapid deployment, non-invasiveness, and avoidance of contrast material. (6)
Multiple studies have demonstrated that physicians from varied disciplines outside of radiology can be highly accurate in finding an AAA using ultrasonography. (7,8,9) Kuhn et al. showed that emergency physicians can identify an AAA with 100% accuracy with only a brief 3 day training course. (7)
The current indications by the American College of Emergency Physicians (ACEP) for obtaining an emergency medicine based ultrasound to detect an AAA include “the presence of syncope, shock, hypotension, abdominal pain, abdominal mass, flank pain, or back pain especially in the older population. (10)
The aorta passes through the diaphragm at the level of the 12th thoracic
vertebral body. It lies slightly to the left of the midline and bifurcates
at the level of the 4th lumbar vertebral body. The surface anatomy
landmarks corresponding to these two points are the xiphoid process and
the umbilicus. The length of the abdominal aorta is about 13 cm (6
inches) which is less than the length of iliac arteries from the bifurcation
to the inguinal ligament. Most scanning of the aorta will therefore
take place in the short distance between the sternum and the umbilicus.
Immediately below the diaphragm, the celiac trunk is the first major vessel to arise from the aorta in the midline anteriorly. This short (usually less than 1 cm) vessel can often be seen sonographically in the transverse plane, dividing in a “wide Y”. The fork on the patient’s right is the common hepatic artery, heading to the porta hepatis; the fork on the patient’s left, is the splenic artery. This sonographic view is known as the “seagull sign”. About 1 cm inferior to the celiac trunk, again in the midline, arises the superior mesenteric artery (SMA), which often runs in a caudal direction immediately anterior and parallel to the aorta. Measurements of the proximal aorta to use as a comparison with distal measurements are made at this level. One centimeter below the SMA, the renal arteries arise on either side. Although these cannot be seen on a sagittal view of the aorta, they can sometimes be identified with careful transverse scanning. Thus, these three major vessels occur within about 3 centimeters of the diaphragm. 90% of all AAA’s will occur distal to this point. With experience, it is easy to distinguish the aorta from the IVC, but initially they can be confused. Distinguishing features are listed in Table 1.
Illustration 1: Overview of the main branches of the abdominal aorta
(CT= celiac trunk, SMA = superior mesenteric artery, IMA = inferior mesenteric artery).
Table 1: Sonographic
features of the aorta vs. IVC.
Figure 1: A transverse image of the aorta shows a classic example of the seagull sign. The celiac trunk branches into the hepatic (H) and splenic (S) arteries. The inferior vena cava (IVC) is seen to the left of the aorta.
III. Scanning Technique, Normal Findings and Common Variants
A 3.5 MHz transducer is adequate for most abdominal scanning, including imaging of the aorta. A lower frequency may be needed in large patients, and a higher frequency will give more detail in thin ones. The aorta and iliac arteries are measured from outer wall to outer wall. The steps for aorta scanning are outlined in Table 2.
Figure 2: Transverse image of the normal proximal
aorta (A) shown in its relationship to the vertebral body (arrow). IVC = inferior
vena cava; H = hepatic artery; L= liver. Figure 3: Transverse image of the normal mid to
distal aorta (A) and inferior vena cava (IVC) before the bifurcation into
the iliac arteries. The vertebral body (arrow) causes a characteristic
Figure 4: Longitudinal view of the normal proximal aorta showing the branches of the celiac artery and SMA. SMA = superior mesenteric artery; VB = vertebral body.
Video clip 1
Video clip 2
Video clip 1: Real time scanning of a normal abdominal aorta in the transverse view. Note the gallstone at the left aspect of the screen in the beginning of the clip. Video clip 2: Real time scanning of a proximal or high normal aorta in the sagittal view.
Special Techniques for Ultrasound Evaluation
If bowel gas makes it difficult to obtain images, some or all the following can help:
- “Jiggle” the probe, while applying gentle pressure. This sometimes allows the bowel to be gently moved aside.
- Reposition the patient.
- Obtain coronal views, using the liver as a window. The probe is placed in the “12 o’clock” position in the mid axillary line at or below the costal margin, directed slightly anterior. With practice, both the IVC and aorta can be seen running parallel in this view, with the aorta lying “deep” on the screen to the IVC.
- Try imaging from below the umbilicus with the probe directed cephalad.
- Try imaging the aortic bifurcation from an oblique angle with the probe placed lateral to the umbilicus (right or left) and pointing towards the spinal column (Figure 5).
Figure 5: Longitudinal-oblique view of a normal lower aorta and bifurcation. (Image courtesy of B. Hoffmann, M.D.)
An AAA is described as being a focal dilatation of the abdominal aorta
of 150% of normal.(11,12,13) Although
there is no established definition of aneurysm size, conventionally, an
AAA is diagnosed when the diameter exceeds 3.0 cm. (1) It
has been demonstrated that the risk of rupture for an AAA of 3.0 cm is
less than 4% over 5 years; this risk, however, substantially increases
for AAA’s with larger diameters. (14)
A true aneurysm by definition involves dilation of all three layers of the aorta: Intima, media, and adventitia. The majority of aneurysms are fusiform, affecting the entire circumference of the vessel. Saccular aneurysms are uncommon and affect only part of the aortic circumference.
Treatment of AAA is entirely surgical. The first resection was performed in Paris in 1951. Prior to that, patients lived with their aneurysms until they ruptured, at which time they usually died. Aneurysms sometimes reached enormous size. In his description, Osler reports on AAAs in living patients, as well as pathological specimens where “the tumour mass… [was] as large as the adult head.” (15)
Figure 6: Transverse image of a nearly 6 cm AAA with calipers measuring the aorta in the anterior-posterior direction.
Figure 7: Transverse image of an AAA with an intraluminal thrombus. This figure demonstrates the importance of measuring the aorta from the outer walls.
Video clip 3
Video clip 4
Video clip 3: Real time transverse imaging of an AAA with an
Video clip 4: Real time transverse imaging of an AAA bifurcating into the iliacs. Notice the presence of an iliac aneurysm.
- Sakalihasan N, Limet R, Defawe OD.
Abdominal Aortic Aneurysm. Lancet.2005;365:1577-89.
- Wilmink AB, Quick CG.
Epidemiology and potential for prevention of abdominal aortic aneurysm. Brit J Surg.1998;85:55–62.
- Ernst CB.
Abdominal Aortic Aneurysm. N Engl J Med.1993;328:1167-72.
- U.S. Preventive Services Task Force.
Screening for abdominal aortic aneurysm: recommendation statement. Ann Inter Med.2005;142(3):198-202.
- Fink HA, Lederle FA, Roth CS, Bowels CA, Nelson DB, Haas MA.
The accuracy of physical examination to detect abdominal aortic aneurysm. Arch Intern Med.2000;160(6):833-6.
- Hermsen K, Chong WK.
Ultrasound evaluation of abdominal aortic and iliac aneurysms and mesenteric ischemia. Radiol Clin N Am.2004;42:365-81.
- Kuhn M, Bonnin RL, Davey MJ, Rowland JL, Langlois SL.
Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate, and advantageous. Ann Emerg Med.2000;36(3):219-23.
- Lin PH, Bush RL, McCoy SA, Felcai D, Pasnelli TK, Nelson JC, Watts K, Lam RC, Lumsden AB.
A prospective study of a hand-held ultrasound device in abdominal aortic aneurysm evaluation. Am J Surg.2003;186(5):455-9.
- Riegert-Johnson DL, Bruce CJ, Montori VM, Cook RJ, Spittell PC.
Residents can be trained to detect abdominal aortic aneurysms using personal ultrasound imagers: a pilot study. J Am Soc Echocardiogr.2005;18(5)394-7.
- American College of Emergency Physicians. Policy Statement.
2001:Emergency Ultrasound Guidelines.
- Johnston KW, Rutherford RB, Tilson MD, Shah DM, Hollier L, Stanley JC.
Suggested standards for reporting on arterial aneurysms. Subcommittee on reporting standards for arterial aneurysms, Ad Hoc committee on reporting standards, Society for Vascular Surgery and North American Chapter, International Society of Cardiovascular Surgery. J Vasc Surg.1991;13:444–50.
- Sox HJ, Huber JM (eds.)
Guide to Clinical Preventive Services, Second Edition, Section I, Chapter 6. Copyright©, Columbia-Presbyterian Medical Center.
- Patel MI, Hardman DT, Fisher CM, Appleberg M.
Current views on the pathogenesis of the abdominal aortic aneurysms. J Am Coll Surg.1995;181:371– 82.
- Vardulaki KA, Prevost TC, Walker NM, Day NE, Wilmink AB, Quick CR, Ashton HA, Scott RA.
Growth rates and risk of rupture of abdominal aortic aneurysms. Br J Surg.1998;85:1674-1680.
- Osler W.
Aneurysm of the abdominal aorta. Lancet.1905;2:1089–96.
- Cronenwett JL, Murphy TF, Zelenock GB, Whitehouse WM Jr, Lindenauer SM, Graham LM, Quint LE, Silver TM, Stanley JC.
Actuarial analysis of variables associated with rupture of small abdominal aortic aneurysms. Surgery.1985;98:472–82.
- Miller J, Grimes P, Miller J.
Case report of an intraperitoneal ruptured abdominal aortic aneurysm diagnosed with bedside sonography. Acad Emerg Med.1999;6(6),661–4.
- Darling RC, Messina CR, Brewster DC, Ottinger LW.
Autopsy study of unoperated abdominal aortic aneurysms. Circulation.1977;56(3) Supp II:161 – 4.