ULTRASOUND ULTRASOUND OF THE OF THE

ABDOMINAL ABDOMINAL AORTAAORTA

(CT= celiac trunk, SMA = superior mesenteric (CT= celiac trunk, SMA = superior mesenteric artery, IMA = inferior mesenteric artery).artery, IMA = inferior mesenteric artery).

ANATOMYANATOMY

ANATOMYANATOMY The aorta passes through the diaphragm at the level of the 12th thoracic vertebral 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 body. It lies slightly to the left of the midline and bifurcates at the level of the 4th lumbar vertebral body. lumbar vertebral body. The surface anatomy landmarks corresponding to these The surface anatomy landmarks corresponding to these two points are the xiphoid process and the umbilicus.two points are the xiphoid process and the umbilicus. The length of the abdominal The length of the abdominal aorta is about 13 cm (6 inches) which is less than the length of iliac arteries from 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 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. 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 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 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”. 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 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. hepatis; the fork on the patient’s left, is the splenic artery. This sonographic view is This sonographic view is known as the “seagull sign”.known as the “seagull sign”. About 1 cm inferior to the celiac trunk, again in the About 1 cm inferior to the celiac trunk, again in the midline, arises the superior mesenmidline, arises the superior mesenteric teric artery (SMA), which often runs in a caudal artery (SMA), which often runs in a caudal direction immediately anterior and parallel to the aorta. Measurements of the 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 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. 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 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 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 occur within about 3 centimeters of the diaphragm. 90% of all AAA’s will occur distal to this point. distal to this point.

With experience, it is easy to distinguish the aorta from the IVC, but initially they With experience, it is easy to distinguish the aorta from the IVC, but initially they can be confused. can be confused.

INDICATIONSINDICATIONS1.1. Screening for aneurysmScreening for aneurysm for patients with for patients with

medical conditions such as diabetes, high medical conditions such as diabetes, high cholesterol and high blood pressure which cholesterol and high blood pressure which increase the risk of developing an abdominal increase the risk of developing an abdominal aorta aneurysmaorta aneurysm

2.2. Evaluate for an aneurysmEvaluate for an aneurysm if a pulsatile mass is if a pulsatile mass is felt on a physical examfelt on a physical exam

3.3. Known abdominal aortic aneurysm and the scan Known abdominal aortic aneurysm and the scan is being done to is being done to check for any change in sizecheck for any change in size of of the aneurysmthe aneurysm

4.4. Evaluate the aortaEvaluate the aorta because of a bruit (rushing, because of a bruit (rushing, whistling noise) of the abdominal aorta heard whistling noise) of the abdominal aorta heard during a physical examduring a physical exam

SCANNING PROTOCOLSCANNING PROTOCOL Patient preparationPatient preparation

Nil orallay 8 hours preceeding to examinationNil orallay 8 hours preceeding to examination Explanation of the procedure to the patients before the examinationExplanation of the procedure to the patients before the examination

The patient should lie comfortably on his/her back. The head may rest on small The patient should lie comfortably on his/her back. The head may rest on small pillowpillow

Apply coupling agent down the midline of the abdomen over a width of 15 cm Apply coupling agent down the midline of the abdomen over a width of 15 cm from below the ribs to the symphysis pubisfrom below the ribs to the symphysis pubis

Choice of transducerChoice of transducer 3.5 MHZ for adults3.5 MHZ for adults 5 MHZ for children5 MHZ for children

Setting the correct gainSetting the correct gain Start by placing the transducer centrally at the top of the abdomen (xiphoid Start by placing the transducer centrally at the top of the abdomen (xiphoid

angle)angle) Angle the beam to the right side of the patient to image the liver; adjust the Angle the beam to the right side of the patient to image the liver; adjust the

gain to obtain the best imagegain to obtain the best image

SCANNING TECHNIQUESCANNING TECHNIQUE

1.1. Orientation. Start in the transverse plane Orientation. Start in the transverse plane (pointer to “9 o’clock”), high in the (pointer to “9 o’clock”), high in the epigastrium, using the liver as a sonic epigastrium, using the liver as a sonic “window”. Identify the vertebral body (a “window”. Identify the vertebral body (a dark, rounded shape, with dense shadow). dark, rounded shape, with dense shadow).

2.2. Identify the aorta on the patient’s left, and Identify the aorta on the patient’s left, and the IVC (patient’s right) “above” the the IVC (patient’s right) “above” the vertebral body on the ultrasound image. (If vertebral body on the ultrasound image. (If the patient is hypovolemic, use light probe the patient is hypovolemic, use light probe pressure in order to avoid effacement of the pressure in order to avoid effacement of the IVC).IVC).

SCANNING TECHNIQUESCANNING TECHNIQUE3.3. In real time obtain transverse images of the In real time obtain transverse images of the

aorta from the celiac to the bifurcation.aorta from the celiac to the bifurcation.

4.4. If the gas-filled transverse colon obscures the If the gas-filled transverse colon obscures the aorta move the probe until you find a aorta move the probe until you find a sonographic window between loops of bowel: sonographic window between loops of bowel: rock the probe up and down without moving rock the probe up and down without moving it across the patient’s skin to maximize the it across the patient’s skin to maximize the information attained through the “window”. information attained through the “window”.

SCANNING TECHNIQUESCANNING TECHNIQUE

5.5. Frequently identifiable “sonic Frequently identifiable “sonic windows” in the upper abdomen windows” in the upper abdomen include:include:

1.1. high in the epigastrium. Ask the high in the epigastrium. Ask the patient to “take a deep breath and patient to “take a deep breath and hold” to lower the liver margin.hold” to lower the liver margin.

2.2. above or around the umbilicus. above or around the umbilicus.

SCANNING TECHNIQUESCANNING TECHNIQUE

6.6. Obtain views of the iliacs if possible. Obtain views of the iliacs if possible.

7.7. Rotate the probe’s pointer clockwise from Rotate the probe’s pointer clockwise from the "9 o' clock" to the “12 o’clock” position the "9 o' clock" to the “12 o’clock” position for sagittal views from the celiac to the for sagittal views from the celiac to the bifurcation.bifurcation.

8.8. Attempt to obtain:Attempt to obtain:1.1. at least 3 transverse views, labeled, “high”, at least 3 transverse views, labeled, “high”,

“middle”, “low”, with calipers. One view “middle”, “low”, with calipers. One view should show the maximal aortic diameter. should show the maximal aortic diameter.

2.2. Sagittal view(s) from the celiac to the Sagittal view(s) from the celiac to the bifurcationbifurcation

SPECIAL TECHNIQUESSPECIAL TECHNIQUES If bowel gas makes it difficult to obtain images, If bowel gas makes it difficult to obtain images,

some or all the following can help:some or all the following can help: ““Jiggle” the probe, while applying gentle pressure. Jiggle” the probe, while applying gentle pressure.

This sometimes allows the bowel to be gently moved This sometimes allows the bowel to be gently moved aside. aside.

Reposition the patient. Reposition the patient. Obtain coronal views, using the liver as a window. Obtain coronal views, using the liver as a window.

The probe is placed in the “12 o’clock” position in The probe is placed in the “12 o’clock” position in the mid axillary line at or below the costal margin, the mid axillary line at or below the costal margin, directed slightly anterior. With practice, both the IVC directed slightly anterior. With practice, both the IVC and aorta can be seen running parallel in this view, and aorta can be seen running parallel in this view, with the aorta lying “deep” on the screen to the IVC. with the aorta lying “deep” on the screen to the IVC.

Try imaging from below the umbilicus with the probe Try imaging from below the umbilicus with the probe directed cephalad. directed cephalad.

Try imaging the aortic bifurcation from an oblique Try imaging the aortic bifurcation from an oblique angle with the probe placed lateral to the umbilicus angle with the probe placed lateral to the umbilicus (right or left) and pointing towards the spinal column(right or left) and pointing towards the spinal column

MEASUREMENT TECHNIQUESMEASUREMENT TECHNIQUES

Obtain measurements of the aorta from outer wall Obtain measurements of the aorta from outer wall to outer wall. Since aneurysms will often contain to outer wall. Since aneurysms will often contain a thrombus, one may accidentally mistake the a thrombus, one may accidentally mistake the inner rim of the thrombus for the aortic wall. inner rim of the thrombus for the aortic wall. Doing this will lead a falsely decreased Doing this will lead a falsely decreased measurement of the true aortic diameter.measurement of the true aortic diameter.

Avoid oblique or angled cuts if possible, especially Avoid oblique or angled cuts if possible, especially with a tortuous aorta, which will exaggerate the with a tortuous aorta, which will exaggerate the true aortic diameter.true aortic diameter.

Although axial resolution is usually greater than Although axial resolution is usually greater than lateral resolution, transverse views are needed lateral resolution, transverse views are needed because many Abdominal aortic anuerysm have because many Abdominal aortic anuerysm have larger transverse than AP diameter.larger transverse than AP diameter.

A transverse image of the aorta shows a classic example of the A transverse image of the aorta shows a classic example of the seagull sign. The celiac trunk branches into the hepatic (H) and seagull sign. The celiac trunk branches into the hepatic (H) and

splenic (S) arteries. The inferior vena cava(IVC) is seen to the splenic (S) arteries. The inferior vena cava(IVC) is seen to the left of the aortaleft of the aorta

SONOGRAPHIC APPEARANCESONOGRAPHIC APPEARANCE

SONOGRAPHIC APPEARANCESONOGRAPHIC APPEARANCE

Transverse image of the normal proximal aorta Transverse image of the normal proximal aorta shown in its relationship to the vertebral body.shown in its relationship to the vertebral body.

SONOGRAPHIC APPEARANCESONOGRAPHIC APPEARANCE

Transverse image of the normal mid to distal aorta and Transverse image of the normal mid to distal aorta and inferior vena cava (IVC) before the bifurcation into the iliac inferior vena cava (IVC) before the bifurcation into the iliac

arteries. The vertebral body causes a characteristic arteries. The vertebral body causes a characteristic shadowing artifact. shadowing artifact.

SONOGRAPHIC APPEARANCESONOGRAPHIC APPEARANCE

Longitudinal view of the normal proximal aorta showing the branches Longitudinal view of the normal proximal aorta showing the branches of the celiac artery and SMA. SMA = superior mesenteric artery; VB of the celiac artery and SMA. SMA = superior mesenteric artery; VB

= vertebral body.= vertebral body.

REFERENCESREFERENCES http://ejechocard.oxfordjournals.org/content/10/5/602.full?maxtoshow=&HITS=10&hi

ts=10&RESULTFORMAT=&fulltext=ultrasound+of+abdominal+aorta&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT#sec-12

http://www.sonoguide.com/abdominal_aortic_aneurysm.html

B.Breyer et.al –Manual of Diagnostic UltrasoundB.Breyer et.al –Manual of Diagnostic Ultrasound