Topic 9 renal arteries

Question 1

Describe the anatomy of the renal arteries

Answer 1

The right renal artery arises at around 10 o’clock from the aorta and passes slightly inferior and under the IVC.
The left renal artery arises at around 3 o’clock from the aorta and is very short. The renal arteries bifurcate into the hilar arteries.

Question 2

Describe primary hypertension

Answer 2

Primary hypertension is persistent elevation of either systolic or diastolic blood pressure, or elevation of both >140/90

Question 3

Describe secondary hypertension

Answer 3

Secondary hypertension is caused by identifiable pathology such as renal artery stenosis, pheochromocytoma etc In many cases it is caused by a chronically stimulated renin-angiotensin system

Question 4

Describe the pathophysiology of renal artery stenosis and increased blood pressure

Answer 4

RAS is a cause of secondary hypertension which directly stimulates the renin-angiotensin system. Angiotensin 2 is vasoactive and will constrict arterial vessels and stimulate aldosterone production from the adrenal glands. Aldosterone promotes reabsorption of sodium and promotes fluid retention. Vasoconstriction and fluid retention promotes an increase in blood pressure. RAS causes hypertension in 2-5% of hypertensive patients.

Question 5

What are some causes of renal artery stenosis

Answer 5

• atherosclerotic stenosis
• chronic renal disease
• fibromuscular dysplasia

Question 6

What is the diagnostic criteria for RAS?

Answer 6

PSV of the renal artery >180cm/s

Ratio of renal artery to aortic PSV >3.5:1

Question 7

How does intrarenal arteries define RAS?

Answer 7

• Absence of the early systolic peak is associated with the presence of significant RAS
• rise of the systolic phase and the time taken to reach the systolic peak
• loss of the early systolic peak and flattening of the systolic upstroke
• Resistive index <0.8

Question 8

How would you better visualise the intrarenal arteries?

Answer 8

• fast sweep speed to better visualise waveforms

- decrease PRF

Question 9

What is an accessory renal artery?

Answer 9

Accessory renal arteries occur in 15-20% of kidneys. They are traditionally not well visualized with ultrasound because they are small and can arise from unusual origins. Incidence of isolated accessory RAS and its significance is not well studied.

Question 10

What is the criteria of renal artery occlusion?

Answer 10

• non-visualisation of a patent artery
• markedly reduced renal length
• multiple tiny arteries without a clear origin or communication to a patent renal artery

Question 11

How are renal transplants attached?

Answer 11

Renal transplants are attached in one of three ways.

1. end of the allograft artery to the side of the EIA
2. end of the allograft artery to an end of an internal iliac artery branch
3. end of multiple allograft arteries to a confluence, known as Carrell’s patch

Question 12

List causes of renal transplant failure

Answer 12

• acute tubular necrosis
• acute rejection
• DVT
• stricture
• pseudoaneurysm
• obstruction of the renal collecting system

Question 13

What do we assess on a renal transplant using colour/spectral Doppler?

Answer 13

• assess the main arterial and venous systems
• focal areas without colour may indicate an infarction
• colour is used to follow the allograft’s vasculature to its communication with the native iliac vessels
• anastomosis is the most common site of arterial abnormality
• kinking, stricture or stenosis from intimal hyperplasia can be identified
• vein is assessed for thrombosis
• patients with end stage renal failure are more prone to develop vascular disease
• assess resistive index of segmental arteries

Question 14

Describe the appearance of a normal renal allograft

Answer 14

There are few differences between a native kidney and an allograft. There may be malrotation. The superficial location of the kidney means that vasculature may be more obvious. Normal ureter may be evident. The transplanted kidney may be considerably enlarged after surgery (20-40%). Failure to enlarge is a marker for renal failure

Question 15

List features of acute rejection.

Answer 15

Specific to rejection:

• increased allograft size (>40%)
• increased cortical volume
• decreased corticomedullary differentiation

Less specific to rejection:

• diffuse or focal hypoechoic change
• decreased echogenicity of renal sinus
• increased resistance in parenchymal arteries (<0.7)

Question 16

Name causes of hydronephrosis in renal transplants

Answer 16

Hydronephrosis can be caused by oedema, haematoma, blood clots and ureteral kinking in the collecting system

Question 17

What is a lymphocele

Answer 17

• most common fluid collection
• can cause hydronephrosis
• most are asymptomatic and resolve over time
• arise from lymphatics damaged by surgery which can cause unilateral leg oedema that can mimic DVT
• seen to arise from the renal hilum
• wedge-shaped when small

Question 18

what is a urinoma?

Answer 18

• cystic mass
• less than 3% of transplants
• source is thought to be from disruption of ureter during surgery or from ureteral necrosis in the setting of rejection
• variable size, irregular, poorly defined and associated with hydronephrosis
• emanate from a ureter

Question 19

list vascular complications of renal transplant

Answer 19

• RAS
• renal artery thrombosis
• renal vein thrombosis
• arterial pseudoaneurysm/AVF

Question 20

Describe a renal transplant arterial pseudoaneurysm/AVF

Answer 20

• bidirectional flow and dilatation of a pseudoaneurysm is similar to peripheral artery setting
• arterilisation of venous flow may occur with a small AVF being created in parenchyma
• may not change renal artery or venous flow but must be identified