Imaging of abdominal aortic aneurysm- ultrasound alone..

1. Aortic aneurysm-
Imaging
Dr. M Sanal kumar
Guided by,
Dr. G Sudha
Dr. T R Saravanan

2. Abdominal aortic aneurysms (AAA) are focal dilatations of the
abdominal aorta that are 50% greater than the proximal normal
segment or that is greater than 3 cm in maximum diameter.
Epidemiology
Its prevalence increases with age.
Males much more commonly affected than females (with a
male:female ratio of 4:1).

3. Clinical presentation
Most AAAs are asymptomatic unless they
leak or rupture.
Unruptured aneurysms may uncommonly
cause abdominal or back pain, or a
pulsatile mass, if large.
Ruptured aneurysms present with severe
abdominal or back pain, hypotension and
shock.

5. Anatomy
The aorta passes through the diaphragm at the level of the T12 vertebral body.
It lies slightly to the left of the midline and bifurcates at the level of L4 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). 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”.

6. About 1 cm inferior to the celiac trunk, arises the superior mesenteric artery
(SMA). 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.. Thus, these
three major vessels occur within about 3 centimeters of the diaphragm.
90% of all AAA’s will occur distal to this point.

7. Most AAAs begin below the renal arteries and end above the iliac
arteries.
The size, shape, and extent of AAAs vary considerably.
Like aneurysms of the thoracic aorta, AAAs may be broadly described
as either fusiform (circumferential) or saccular (more localized).

9. Causes
Atherosclerosis (most common)
Inflammatory abdominal aortic aneurysm
Chronic aortic dissection
Vasculitis, e.g. Takayasu arteritis
Connective tissue disorders, e.g.
Marfan syndrome
Ehlers-Danlos syndrome
Mycotic aneurysm
Traumatic pseudoaneurysm
Anastomotic pseudoaneurysm

10. The natural history of abdominal aortic aneurysms (AAA) is that of
slow expansion and rupture with devastating consequences.
The risk of rupture is proportional to the size of the aneurysm and
the rate of growth.
Differing rates of rupture for a given aneurysm size have been
reported in the literature but the general consensus is that
aneurysms greater than 5.0 cm in women and 5.5 to 6.0 cm in men
carry a significantly increased risk of rupture and should be
treated.
Furthermore, aneurysms that expand greater than 10 mm per year
are also at significant risk of rupture and are considered for
treatment even when less than 5.0 cm.

11. Ultrasound
Ultrasound assessment is simple, safe and inexpensive.
It has a reported sensitivity of 95% and specificity close to 100%.
It is usually the preferred choice for monitoring of small aneurysms.

12. Technique for ultrasound scanning of the aorta
1) Orientation. Start in the transverse plane (pointer to “9 o’clock”), high in the
epigastrium, using the liver as a sonic “window”. Identify the vertebral body (a
dark, rounded shape, with dense shadow).
2) Identify the aorta on the patient’s left, and the IVC (patient’s right) “above” the
vertebral body on the ultrasound image.
3) In real time obtain transverse images of the aorta from the celiac to the
bifurcation.
4) Obtain views of the iliacs if possible.
5) Rotate the probe’s pointer clockwise from the "9 o' clock" to the “12 o’clock”
position for sagittal views from the celiac to the bifurcation.
6) Attempt to obtain:
1) at least 3 transverse views, labeled, “high”, “middle”, “low”, with
calipers. One view should show the maximal aortic diameter.
2) Sagittal view(s) from the celiac to the bifurcation

17. Aorta is visualized first in short axis and then in long axis. Large (>7 cm) abdominal
aortic aneurysm with mural thrombus and hypoechoic areas is noted outside aorta,
which may represent rupture. Colorflow Doppler illustrates turbulent flow within lumen.

18. Using Sonography to Monitor the Growth of an
Abdominal Aortic Aneurysm
The accepted method of monitoring abdominal aortic aneurysm is as follows:
If aneurysm measures < 4cm in diameter, the patient is scanned once each year.
If aneurysm measures between 4cm- 5cm in diameter, the patient is scanned
every 6 months.
If aneurysm measures between 5cm - 5.5cm in diameter, the patient is scanned
every 3 months.
Once the aneurysm reaches 5.5cm in diameter, the patient is scheduled for
surgical repair.
It is important to repair the aneurysm before the diameter reaches 6cm because of
increased risk of rupture.
If an aneurysm is growing rapidly, repair be scheduled sooner to avoid rupture.

19. The mortality rate from a ruptured AAA is high (59-83%) of
patients succumb to death before they make it to hospital or
undergo surgery. The operative mortality rate for those who make
it to surgery tends to be around 40%.

20. Pearls and Pitfalls
•Obtain measurements of the aorta from outer wall to outer wall. Since
aneurysms will often contain a thrombus, one may accidentally mistake the
inner rim of the thrombus for the aortic wall. Doing this will lead a falsely
decreased measurement of the true aortic diameter.
•Avoid oblique or angled cuts if possible, especially with a tortuous aorta,
which will exaggerate the true aortic diameter.
•Transverse views are needed because many AAAs have larger transverse than
AP diameter.
•A small aneurysm does not preclude rupture: Any symptoms consistent with
rupture in a patient with an aortic diameter greater than 3.0 cm should have
this diagnosis (or alternative vascular catastrophes) ruled out.
•Scanning should be systematically performed in real-time from the
diaphragmatic hiatus to the bifurcation in order to avoid missing small,
localized saccular aneurysms.