Sonography of the Aorta - HD

Introduction

Good morning.
I'm Wei Chung from the University of North Carolina,
and I'm gonna be talking about ultrasound of the aorta.

Anatomy of the Abdominal Aorta

I will briefly describe the anatomy of the abdominal aorta.
The abdominal aorta runs from the aortic HIAs
to the bifurcation.
It has three major anterior branches,
the celiac axis at T 12, the SMA at L one,
the IMA at L two.
It has multiple paired branches,
of which the most significant are the renal arteries.
At T two, the gonadal arteries,
and there are four paired lumbar arteries.
This, these are the gonadal arteries,
the celiac artery,
and the SMA arise from the anterior aspect
of the proximal aorta.
This is the celiac axis,
and this is the SMA in one to 3%
of patients the celiac artery
and the SMA arise from a common trunk.
This is the common trunk coming off here
and giving off the celiac
and the SMA from the abdominal aorta.

Technique

Measure the aorta
and common iliac arteries from the outer diameter in the AP
and transverse planes.

Doppler Tips

Aliasing is a marker of stenosis.
The doppler spectrum should be obtained from the site
of aliasing or turbulent flow.
In this case from the origin of the celiac axis, where
an area
of aliasing is seen indicating a stenosis at
the celiac axis.
Elevated velocities are seen within the stenosis
and tardis pelvis wave forms are seen
distal to the stenosis.

Normal Measurements

The normal aorta is larger in the males than in females.
It increases with age.
At the aortic HIAs,
the normal male aorta measures 2.7 centimeters.
In females, it measures 2.3 centimeters.
At the bifurcation, the aorta measures 2.1 centimeters.
In the females, it measures 1.7 centimeters.
The non normal common ECT artery should be less than 1.5
centimeters in size.
This image shows the appropriate way to measure the
aorta in the transverse plane.
The doppler wave form of the normal aorta is phasic
with early diastolic reversal of flow.
Lower resistance, IE more diastolic flow is seen in the
proximal aorta before the takeoff
of the renal arteries than in the distal aorta.
Peak systolic velocity in the normal aorta is 110
centimeters per second.
When young, with increasing age, this decreases to 70
to a hundred centimeters per second.

Risk Factors for Abdominal Aortic Aneurysm

Hypertension, smoking, family history, age,
connective tissue disease infection,
and this is called mycotic aneurysm.
Inflammation and trauma,

Growth and Rupture of Abdominal Aortic Aneurysms

Abdominal aortic aneurysms
increase in size with time.
There is high variability in growth rates.
The rate of growth increases as the aneurysm grows.
Growth rate is increased in smokers.
Abdominal aortic aneurysm has been called the silent killer
because it is asymptomatic
and can rupture suddenly resulting in high mortality.
Lala's law describes the relationship between the diameter
of the aorta and the pressure on the wall.
Essentially, the larger the aneurysm,
the greater the pressure on the wall of the aorta
and the greater the risk of rupture incidence
of rupture rises.
Therefore, with aortic diameter, it is
for di uh, for aortas that are three
to five centimeters in diameter, it is 1% per year.
When the aneurysm increases to greater than 5.5 centimeters,
it is 10% per year.
The rupture rate is increased in active smokers.
These are two famous people who died
of ruptured aortic aneurysm.
On the right is the scientist, Albert Einstein.
On the left is the entertainer. Lucille Ball.

Screening and Surveillance

Abdominal aortic aneurysm screening and surveillance has
therefore, uh, been developed in several countries
to prevent aortic, uh, uh, rupture
before the aortic aneurysms get too large.
In the United States, uh, this is in the form
of the Safe Act
or stopped abdominal aortic aneurysm very efficiently.
It implements screening for abdominal aortic aneurysm
as a Medicare benefit
and specifies ultrasound as the screening modality.
Every man over 65 and every woman with a family history
or every male smoker is entitled to one screening.
Ultrasound exam Screening has been shown
to reduce the mortality of abdominal aortic aneurysm by 21
to 48% in the United Kingdom.
The multicenter aneurysm screening study,
or mass randomized trial
of abdominal aortic screening was carried out.
67,000 men age 65
to 74 were divided into screening and control groups.
In the screen group,
there were 224 abdominal aortic aneurysm related deaths.
While there were 381 abdominal aortic aneurysm related
deaths in the control group
resulting in a 42% reduction in abdominal aortic
aneurysm related deaths.
As a result of screening.
Overall, the patients in the screen group had a 3%
reduction in all deaths.
This results in one life save
for every 216 screened patients.

Management of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm can be managed by surgery
or endovascular repair.
The mortality rate of elective surgery is 5%,
while the mortality of endovascular repair is
two to 5%.
In recent years, endovascular repair has become the
treatment of choice
for abdominal aortic aneurysm.
When the aneurysm exceeds 5.5 centimeters in
diameter, the risk
of rupture is greater than the surgical risk, and
therefore, either surgery
or endovascular repair is indicated
for smaller aneurysms between four and 5.4 centimeters.
Surgery offers no survival advantage
for aneurysms under 5.5 centimeters.
There are medical Managements
that reduce the rate of growth.
These include smoking cessation
and trials are underway, evaluating beta blockers, statins,
antiplatelet drugs, and ACE inhibitors.

Measurements of the Abdominal Aorta

Measurements of the abdominal aorta should be obtained in
the longitudinal and transverse plane perpendicular
to the long axis.
Measurements should be performed from the outer wall
to the outer wall, and the length
of the aneurysm should be measured.
Additionally, the location
of the measurements should be recorded.
Most abdominal aortic aneurysms occur inferior
to the origin of the renal arteries, but a few occur SRE
or juxta renal, and these should be recorded.
A diagnosis of abdominal aortic aneurysm is made when the
diameter of the aorta exceeds three centimeters
or increases to 1.5 times greater than that
of the adjacent normal aorta.
A common iliac artery aneurysm is diagnosed when the
diameter exceeds 1.5 centimeters.
When an aneurysm has been diagnosed, the policy is
to follow up a three to four centimeter aneurysm annually,
a four to 4.5 centimeter aneurysm every six months
for aneurysms greater than five centimeters.
These should be followed up every three months.
If no treatment is planned, focal ectasia
or bulging should be followed every two to three years.

Measurement Technique

On the left is the wrong way
to measure an abdominal aortic aneurysm.
The calipers have been placed on the inner
or intimal surface of the aorta
On the right is the correct way.
The measurement caliper has been placed on the outer surface
of the aorta, and the correct distance is from the outer
surface of the aorta here to the outer surface of the aorta.
Here,
measurement technique, patients should be fasted
for eight to 10 hours.
A 2.5 megahertz coline transducer should be used.
Compression may be applied to eliminate bowel gas.
Another useful maneuver to eliminate bowel gas is
to place the patient in the left lateral decubitus position.
Lung axis views of the kidneys should be obtained.
Measurements should be obtained from the proximal mid
and distal aorta.
The common ECT arteries should be
measured at the bifurcation.
For screening purposes,
a single transverse measurement will suffice.
It is important to obtain the measurements perpendicular
to the plane of the vessel.
The aorta can be a very torturous structure,
and in this case here, the correct diameter
of the aorta on this CT uh, angiogram image.
The correct way to measure the diameter
of this aorta would be
to place the transducer in a slightly oblique orientation
because that is perpendicular to the course of the aorta.
If the transducer is placed in a true transverse plane,
an erroneous measurement will be obtained.
This will result in overestimation of the luminal diameter.

Common Pitfalls

This slide illustrates a common pitfall.
In this case, the inner wall
of a thrombus is mistaken for the wall of the aorta.
This echogenic line actually represents the surface
of a large thrombus that is lining the wall
of an abdominal aortic aneurysm.
On the transverse view,
the cresent shaped thrombus is better seen.
The true position of the
aortic wall is marked
by the open arrow on the longitudinal image
and by the open arrows on the transverse image,
and the true diameter of the Aneurysm is shown
by the position of these calipers.
In aneurysms with thrombus,
turbulent flow can be seen with dopplar.
On this image. Here we see an abnormal aortic waveform
with turbulent flow and spectral broadening.
The color Doppler image shows turbulence
while the thrombus itself is markedly hypo coic
and not well seen on the gray scale portion of the image.

Aortic Rupture

Aortic rupture is a surgical emergency.
Non contrasted CT is the preferred modality
for detecting aortic rupture,
and ultrasound has no place
in this situation.
However, if ultrasound is performed, a perio hematoma
or hemoperitoneum may be seen.

Aortic Dissection

Dissection of the abdominal aorta is separation
of the medial and interal layers of the aortic wall.
A dissection within the abdominal aorta results from
extension of a thoracic dissection,
so nearly all abdominal aortic dissections
originate in the thorax.
On the illustration here, a dissection is shown
where the blood passes through
a hole within the intima
and into the aortic wall itself,
separating out the intima from the
medial and serosal layers.
This pocket where the
blood has passed into the abdominal wall is known
as the false lumen.
Aortic dissection is associated with
abdominal aortic aneurysms, ulcers, hypertension,
atheroma maan syndrome, aless down loss,
trauma, and pregnancy.
In aortic dissection, the false lumen is usually larger
and maybe thromboses.
The false lumen shows two and fro flow on spectral doppler,
and it is important when evaluating dissections
to evaluate the patency of the branches
of the abdominal aorta in that vicinity
because the dissection can result in
obstruction of these branches.
This is an image of an aortic dissection.
This longitudinal image demonstrates a linear hyper
echogenicity within the lumen of the
representing the dissection flap.
The false and true lumens are shown
and flow is seen in both the false
and true lumens in this patient.
If doppler spectra are obtained from the false
and true lumens, bizarre spectra may be seen in this case,
there is a dissection flap
seen within the abdominal aorta on this transverse image.
A spectrum is obtained that is bizarre
and has does not resemble any physiologic aortic waveform.

Conclusion

In conclusion, ultrasound is the modality of choice
for detection and follow up of abdominal aortic aneurysm.
CT is the preferred modality for detection of rupture. I.