Topic 8 aorta and mesentery

Question 1

Describe the celiac axis

Answer 1

The celiac axis is the first branch of the abdominal aorta. It arises from the ventral surface in most people. Gives rise to the splenic, hepatic and left gastric arteries. Supplies the spleen, pancreas, stomach, upper duodenum and liver

Question 2

Describe the superior mesenteric artery.

Answer 2

Lies immediately below to the celiac trunk, but might share a common origin with the celiac artery. The SMA supply the rest of the small intestine (except for the proximal duodenum), most of the transverse colon, caecum and the ascending colon

Question 3

Describe the inferior mesenteric artery

Answer 3

The IMA arises 3-4cm above the aortic bifurcation from the left anterior surface of the aorta. It arises anteriorly and passes left to the aorta. Supplies the left 1/3 of the transverse colon, the sigmoid colon and the rectum.

Question 4

Describe the right renal artery

Answer 4

The right renal artery arises just inferior to the SMA and passes under the IVC, slightly inferior to the renal hilum. At the hilum, the RRA branches into posterior and anterior branches which give rise to segmental arteries supplying each pole of the kidney.

Question 5

Describe the left renal artery

Answer 5

The left renal artery arises just inferior to the RRA and is shorter due to the close proximity of the aorta and the left kidney. Usually forms a more acute angle to reach the hilum of the left kidney before it branches

Question 6

Explain the pathophysiology of an aortic aneurysm

Answer 6

Aneurysms form as a result of the imbalance of elastin and collagen in the arterial wall. The tunica media is most affected by the loss of elastic tissue, producing a thin and fibrotic wall. Aneurysms are areas of arterial dilatation relative to the adjacent normal arterial segment.

Question 7

What size aortic aneurysms is considered for surgical/endolumninal repair?

Answer 7

> 5 cm

Question 8

What is considered ectatic or aneurysmal of the iliac arteries?

Answer 8

> 1 cm

Question 9

What is the 3rd most common type of aneurysm?

Answer 9

Popliteal aneurysm. CFA aneurysms coexist with 40% of popliteal aneurysm. 50% of people with a popliteal aneurysm will also have an aortic aneurysm

Question 10

What is an aortic dissection?

Answer 10

Aortic dissection is the splitting of the intraluminal layers causing a tear between the intima and media layers. Most dissections are seen in the thoracic aorta and are asses on arteriography or transoesophageal techniques.

Question 11

Define the DeBakey classification of aortic dissection.

Answer 11

Type 1: involves ascending aorta, arch and the descending thoracic aorta. It may progress to involve the abdominal aorta.

Type 2: is confined to the ascending aorta

Type 3A: involves the descending thoracic aorta distal to the left subclavian artery and proximal to the celiac artery

Type 3B: Dissection involves the thoracic and abdominal aorta distal to the left subclavian artery

Question 12

Define the Stanford classification of aortic dissection

Answer 12

Type A: involves the ascending aorta and may progress to involve the arch and the thoracoabdominal aorta

Type B: involves the descending thoracic or thoracoabdominal aorta distal to the left subclavian artery without involvement of the ascending aorta

Question 13

What are risk factors for a AAA?

Answer 13

• family history
• male
• smoking
• increased age

Question 14

What are techniques to assess the aorta when there is decreased visualisation?

Answer 14

• use the anterior oblique plane to improve visualisation
• anterior and left for the upper aorta
• anterior and right for the lower aorta

Question 15

How should we assess the iliac arteries?

Answer 15

In the sagittal plane, this is more accurate as the iliacs often diverge at a sharp angle which makes a true trans alignment difficult

Question 16

What should be noted when a AAA is present?

Answer 16

• measure diameter in AP and coronal planes
• diameter of the aorta at the renal arteries
• length of the aneurysm
• distance from the bifurcation to the end of the aneurysm
• size of the patent lumen if mural thrombus is present
• diameter of iliac artery dilation
• location in terms of the renal arteries

Question 17

How do you know if you are perpendicular to the artery?

Answer 17

Obtain a transverse view and slowly tilt the beam superiorly and inferiorly. As the beam becomes oblique, the wall will appear slightly thickened and less clear

Question 18

What are strategies to overcome overlying bowel?

Answer 18

• alternate positioning
• subtle movement and angulation
• gentle graded compression
• fasting
• lower frequency transducer

Question 19

What strategies can be used to overcome calcification?

Answer 19

Different patient positioning

Question 20

How would you improve visualisation of mural thrombus?

Answer 20

• use colour flow imaging
• use colour power imaging
• higher dynamic range
• alter patient position or transducer position

Question 21

How would you improve visualisation of an aortic dissection/intimal flap?

Answer 21

• high gain setting
• increased dynamic range
• colour to look for a patent false lumen
• dissection will move as the image of the aorta moves
• if the false lumen has thrombosed, it is often impossible to confirm the presence of a dissection

Question 22

Describe a surgical repair of the aorta

Answer 22

• Aorta is repaired surgically by opening the aneurysmal artery and placing a synthetic tube inside
• tube is stitched to the non-aneurysmal artery at each end to make a tight seal and the aorta is sewn over the tube
• bifurcated tube is used if the iliac arteries require repairing

Question 23

Describe an EVAR

Answer 23

• mesh stent which is lined with a non-porous material to exclude the aneurysmal sac and to provide a new conduit for blood to flow
• the aneurysm will remain but decrease in size with time
• stents are placed via catheters inserted into both femoral arteries
• risk of endograft leak, thrombosis and stent migration

Question 24

What is acute mesenteric ischaemia?

Answer 24

AMI results from acute embolic occlusion or thrombosis of the mesenteric arteries, mesenteric vein thrombosis or non-occlusive ischaemia. Emboli usually arise from cardiac origins but can come from proximal aortic atheroma or paradoxic emboli from venous circulation. This is an urgent diagnosis and angiography is the main method of diagnosis

Question 25

What is non-occlusive ischaemia associated with?

Answer 25

Non-occlusive ischaemia is mostly due to vasoconstriction of mesenteric vessels and mesenteric vein thrombosis due to sepsis or from idiopathic causes

Question 26

What is chronic mesenteric ischaemia?

Answer 26

CMI is caused by the development of atherosclerosis and its consequent effect on pressure and flow to the mesenteric circulation. Patients will usually have abdominal pain within 30 minutes after eating and show significant weight loss. Abdominal bruit is the most common indication. Patients will commonly have coexisting vascular and coronary artery disease

Question 27

What is post-prandial testing

Answer 27

In a fasted state, the bowel is at rest and requires little blood. At this state, arteries in the bowel wall are constricted. Eating a significant meal triggers an immediate vasodilation as the blood vessels increase activity and absorption. In the event of significant stenosis, insufficient blood pressure will invoke an ischaemic response similar to claudication.

Question 28

Describe mesenteric artery ultrasound technique

Answer 28

The patient must be fasted. Small amounts of water is allowed.

Arteries to assess:

• SMA
• Celiac axis
• Hepatic artery
• Splenic arter
• IMA
• Aorta

Question 29

How would you scan the SMA?

Answer 29

• Patient is supine
• SMA runs inferiorly at an angle which is good for spectral analysis
• Generally doesn’t have branches, but in 20% of people there will be a replaced right hepatic artery
• Assess in b-mode and colour
• Place a spectral trace at the origin, proximal and mid artery

Question 30

How would you scan the celiac axis?

Answer 30

• Patient is supine
• the celiac axis is short
• the left gastric artery is rarely seen
• assess in b-mode and colour
• spectral trace at the origin and mid artery

Question 31

What is median arcuate ligament syndrome?

Answer 31

• There will be focal increase in velocity isolated to the origin of the celiac axis in a young, thin patient, extrinsic compression of the celiac axis can be caused by the median arcuate ligament. it is often a source of abdominal bruit and abdominal pain. Pain results from the superior movement of the aorta during expiration. If velocity increase is noted at the celiac origin, then scan the patient on inspiration and expiration.

Question 32

How would you scan the IMA?

Answer 32

• IMA is usually visible from a 12 o’clock position arising slightly to the left
• If the IMA is hypertrophied, then this is an indicator of disease in other vessels

Question 33

Define the criteria for >70% stenosis in the SMA

Answer 33

• PSV > 275 cm/s
• EDV > 55cm/s
• high resistance waveform
• PSV > coeliac axis in the normal patient

Question 34

Define the criteria for >70% stenosis in the celiac axis, hepatic artery and splenic artery

Answer 34

• PSV > 200cm/s
• EDV> 45 cm/s
• Lower resistance waveform
• PSV < SMA in the normal patient

Question 35

Define the criteria for >50% stenosis in the IMA

Answer 35

PSV >200cm/s

Question 36

What is a portosystemic shunt?

Answer 36

Portosystemic shunts relieve symptoms of portal hypertension. They are inserted using an endovascular approach. They relieve hypertension to protect the patient from oesophageal variceal bleeding. Common shunts are transjugular, intrahepatic and portosystemic.

Question 37

What are complications of portosystemic shunts?

Answer 37

The often become stenosed or occluded

Question 38

What should an ultrasound of a portosystemic shunt show?

Answer 38

• Spectral traces should be compared to the baseline which is completed within the first 24 hours
• image flow in the PV, SMV, splenic vein and hepatic veins
• image the shunt
• scan should demonstrate the end of shunt in native vessel, good colour fill, low impedance waveform with some pulsatility, 50-60cm/s PSV, similar velocities at either end of the shunt, hepatopetal flow in the PV, PV >30cm/s

Question 39

What are indications of TIPS abnormality?

Answer 39

• focal or diffuse narrowing
• increased PSV
• very low PSV

Question 40

What happens in a pancreas transplant?

Answer 40

The entire pancreas is often transplanted with a loop of duodenum which is anastomosed to the bladder. Organs can be susceptible to rejection, anastomotic leaks, arterial and venous anastomotic complications. Ultrasound can detect peripancreatic collections or pancreatic enlargements. Colour duplex is used to evaluate vasculature

Question 41

What is the Milan criteria?

Answer 41

Criteria to assess suitability in patients for liver transplantation due to cirrhosis or hepatocellular carcinoma.

• single tumour with a diameter of ≤5 cm, or up to 3 tumours each with diameter ≤3 cm
• no extra-hepatic involvement
• no major vessel involvement