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Son5025 Vasc > Topic 10 -renal arterial and renal transplant > Flashcards

Topic 10 -renal arterial and renal transplant Flashcards

1
Q

Describe the anatomy of the renal arteries

A
  • the right renal artery (RRA) arises at around 10 o’clock from the aorta and then passes slightly inferiorly and under the IVC.
  • The left renal artery (LRA) arises at around 3 o’clock from the aorta and very shortly after its origin passes posteriorly into the renal gutter.
  • This places it deep behind the stomach and bowel which can make it difficult to visualise.
  • The renal arteries bifurcate at any point along their length and can have a multitude of bifurcations.
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2
Q

What is the route of the left renal vein?

A

Over the aorta and under the sma

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3
Q

What is hypertension?

A

persistent elevation of either systolic or diastolic blood pressure or elevation of both pressures with a diastolic pressure of greater than 90 mmHg and/or a systolic pressure greater than 140mmHg.

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4
Q

What are the causes of primary hypertension?

A

Poorly understood

• Blood pressure is determined by cardiac output and total peripheral resistance

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5
Q

What is secondary hypertension?

A
  • caused by an identifiable pathology such as renal artery stenosis, chronic renal disease, pheochromocytoma, hyper or hypo thyroidism, aortic coarctation etc.
  • In many of these cases, the renin-angiotensin system is chronically stimulated while in other conditions such as pheochromocytoma, there is a significant release of catecholamines which cause vasoconstriction.
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6
Q

How does renal artery stenosis cause hypertension?

A

• a cause of secondary hypertension which directly stimulates the renin-angiotensin system.

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7
Q

What is an effect of RAS other than hypertension?

A

In addition to raising blood pressure
• atherosclerotic stenosis can result in ischemic nephropathy by causing fibrosis of the glomerulus and damage to the endothelium of the blood vessels in the nephron and eventually loss of nephrons.

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8
Q

What other kidney disease can cause hypertension?

A

• Similarly, chronic renal disease can also trigger the renin-angiotensin system which causes hypertension.

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9
Q

Why does treating RAs have an unpredictable result?

A

thought to relate to the degree of nephron damage in the kidney prior to its treatment.

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10
Q

Why is ultrasound assessment of RAS valuable?

A
  • ultrasound has its value in being non invasive and not using contrast agents
  • which will increase the risk of contrast induced acute renal failure in those with impaired renal function.
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11
Q

What are some difficulties in using ultrasound to assess RAS?

A 
o	overlying bowel gas
o	obese patients
o	multiple renal arteries
o	low blood flow velocities
o	respiration
o	patient movement
o	calcification
o	tortuosity
o	attenuation from the renal sinus fat
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12
Q

What are the two ways of assessing RAS?

A
  • direct

* indirect

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13
Q

How is RAS directly assessed?

A
  • requires assessment of the length of both renal arteries
  • It is very important to use colour Doppler to screen the length of the artery, whether from one single view or from multiple approaches so the length of the artery is examined.
  • The diagnostic criteria for renal artery stenosis uses the absolute peak systolic velocity (PSV) in the renal artery or a ratio of the renal and adjacent aortic PSV.
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14
Q

How is RAS indirectly assessed?

A

• identify an intra renal waveform from the segmental or interlobar arteries
- observe the deflection or ‘notch’ in the latter part of the systolic upstroke.
• This notch is termed the early systolic peak (ESP) and its absence was associated with the presence of significant renal artery stenosis.
• In addition to the ESP, the rate of rise of the systolic phase and the time taken to reach the systolic peak can also be used to identify significant stenosis.
- no longer used

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15
Q

How is resistance index use in RAS assessment?

A
  • resistive index greater than 0.8 had no resolution of their hypertension after treatment.
  • This type of intrarenal assessment can be used as a broad predictor of treatment outcome.
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16
Q

What are the criteria for RAS in direct assessment?

A

renal artery: aorta (RAR) ratio > 3.5:1
PSV > 180cm/s
These numbers vary slightly within the literature

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17
Q

What are the criteria for indirect assessment?

A
  • pattern recognition: normal, equivocal, abnormal
  • loss of early systolic peak and flattening of the systolic upstroke is a marker for abnormality
  • resistive index: variation of > 0.05 (marker for abnormality)
  • resistive index: < 0.8 suitable for intervention
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18
Q

What is the best way to approach assessment of the proximal renal arteries?

A

with a transverse view in one of three positions:
• just below the sternum with the transducer beam pointed slightly inferior
• at the epigastric level
• slightly above the umbilicus with the transducer beam pointed superiorly

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19
Q

What is the best way to approach assessing the distal renal artery?

A

typically viewed more effectively from a lateral view, looking through the kidney in either a long or transverse plane.
An inferior lateral view can also be effective for this location.

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20
Q

What can suggest renal artery occlusion?

A

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

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21
Q

What is the average life expectancy of a renal allograft?

A

cadaveric allograft is 7 to 10 years, whereas that for a live donor allograft is 15 to 20 years

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22
Q

Where will you commonly find a renal allograft?

A

right iliac fossa

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23
Q

What are the three types of vascular anastomosis in renal trasnplant surgery?

A
  • at the end of the allograft artery to the side of the EIA (end to side)
  • at the end of the allograft artery to an end of an internal iliac artery branch (end to end)
  • at the end of multiple allograft arteries to a confluence – known as Carrell’s patch.
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24
Q

What dictates the type of arterial renal allograft anastomosis?

A

arterial anastomosis used depends on whether the allograft is cadaveric or living related
• cadaveric transplants, the donor artery, along with a portion of the aorta (Carrel patch) are anastomosed end to side to the external iliac artery.
• living donor transplants, the donor renal artery is anastomosed to either the internal iliac artery (end to end) or the external iliac artery (end to side) of the recipient.

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25
Q

How is the donal renal vein anastomosed?

A

• Almost always anastomosed end to side to the external iliac vein.

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26
Q

How is the donor ureter anasomtosed?

A

• usually anastomosed to the superolateral wall of the urinary bladder through a neocystostomy.

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27
Q

What are the potential complications of renal transplant?

A 
Acute tubular necrosis (ATN)
acute rejection
DVT are not uncommon occurrences. 
Stricture
pseudoaneurysm
obstruction of the renal collecting system may also affect the allograft.
28
Q

What are the primary tools for assessing the renal allograft?

A

Renal function is of primary importance, so for this reason blood tests and nuclear medicine scanning with DPTA are a primary diagnostic tools. The assessment of the arterial system has angiography as the gold standard.

29
Q

How does the normal renal allograft appear on ultrasound?

A
  • There are very few differences between a native kidney and the allograft
  • there may be an apparent malrotation.
  • The peri-renal area is markedly different.
  • The typical transplanted kidney is considerably enlarged after surgery.
  • This begins at around two weeks post transplantation and continues until around six months.
  • Failure to enlarge may be a marker of renal failure.
  • Renal allografts also contain less renal sinus fat.
30
Q

What are some sonographic findings of renal allograft rejection?

A

Specific to rejection:
• increased allograft size
• increased cortical volume
• decreased cortico-medullary differentiation
Less specific to rejection:
• diffuse or focal hypoechoic change
• decreased echogenicity of the renal sinus
• increased resistance in the parenchymal arteries

31
Q

What should the resistance of parenchymal arteries in the renal allograft be?

A

ideally less than 0.7.
A resistance of greater than this may indicate a compromised kidney.
The specificity of this finding is increased if we use 0.8 or even 0.9 but will reduce sensitivity. T
his is of more value in predicting other abnormalities and is of questionable use in defining rejection

32
Q

How does acute tubular necrosis appear on ultrasound?

A
  • This is generally seen in the initial post operative period.
  • Ultrasound is disappointing in this diagnosis.
  • Neither size nor cortical echogenicity is of any assistance.
  • Occurs most often in cadaveric grafts
33
Q

How is chronic rejection defined?

A

• reduction in allograft function starting at least 3 months after transplantation in association with fibrous intimal thickening, interstitial fibrosis, and tubular atrophy on histology.

34
Q

What is the biggest risk factor for chronic renal allograft rejection?

A

• The most frequent predisposing risk factor for development of chronic rejection is recurrent previous episodes of acute rejection.

35
Q

How does chronic rejection appear on ultrasound?

A

• progressive thinning of the renal cortex
- prominence of the central renal sinus fat
- a reduction in the overall size of the transplant.
• Dystrophic calcifications may be seen scattered throughout the residual parenchyma.
• In the end-stage renal transplant, the entire renal cortex can become calcified,

36
Q

What is the role of ultrasound in assessing renal allograft complications?

A

limited role in differentiating rejection from other parenchymal abnormalities.
The presence of a number of sonographic features will support the diagnosis of rejection in an advanced stage, but biopsy is the only method which will confirm the nature of the rejection.

37
Q

What are some causes of obstruction in the renal allograft?

A

oedema, haematoma, blood clots and uretal kinking can cause a dilated collecting system.
• A large cystic structure may be a consequential urinoma or lymphocele.
• Strictures are another complication which may cause obstruction.
• These will most likely occur at the PUJ.

Bladder dysfunction

38
Q

What are the peri nephric fluid complications associated with renal allograft?

A

• This is an important group as they may represent a nidus of infection or a source of mechanical obstruction.
• Ultrasound is a very important diagnostic tool for the evaluation of this group.
- lymphocele
- haemotoma
- urinoma
- Post surgical seroma

39
Q

What is lymphocele?

A
  • the most common fluid collection detected
  • occurring in up to 20 percent of patients.
  • Lymphoceles result from surgical disruption of the iliac lymphatics
  • most often occur 4 to 8 weeks after surgery
  • may develop years after transplantation
  • most are discovered incidentally and are asymptomatic
40
Q

How do lymphocele appear on ultrasound?

A
  • On sonography, lymphoceles are well-defined collections that are anechoic or that may contain fine internal strands
  • The smaller lymphoceles are wedge shaped and generally lie posterior to the native vessel.
  • Septations may occasionally occur.
41
Q

What are some clinical signs of lymphocele?

A
  • Most are asymptomatic and will resolve over a period of time.
  • They can be the cause of hydronephrosis appearing early post surgically or in the chronic phase.
  • The lymphoceles that arise from lymphatics damaged by surgery may cause unilateral leg oedema.
  • This may mimic DVT.
42
Q

What is the second most common fluid collection seen at renal allograft?

A

haemotoma

43
Q

How does allograft haematoma appear on ultrasound?

A
  • these are often asymptomatic and are an incidental finding at this examination.
  • Typical of haematoma, they can be varied in their appearance on ultrasound ranging from quite solid, to almost cystic.
  • An acute hematoma will appear as an echogenic heterogeneous solid mass. With time the hematoma will liquefy, becoming a complex fluid collection with internal echoes, strands, or pseudoseptations.
44
Q

What is a urinoma?

A
  • Aka urine leaks
  • another cystic type mass that may appear
  • these are much more unusual, appearing in less than three percent of transplants
45
Q

What causes a urinoma?

A
  • Their source is thought to be disruption of the ureter during surgery or from uretal necrosis in the clinical setting of rejection.
  • Failure of the uretal anastomosis is uncommon.
46
Q

How do urinomas appear on ultrasound?

A

varied in size, irregular, poorly defined and associated with hydronephrosis.

47
Q

What is a post surgical seroma and how does it appear on ultrasound of the renal allograft?

A
  • Common immediately after surgery and resolve shortly after this time.
  • Septations are common and it is a difficult lesion to differentiate from the other cystic masses.
48
Q

What are the general rules in differentiating peri nephric fluid collections according to location?

A
  • Urinomas will emanate from a ureter.
  • Lymphoceles will be seen arising from the renal hilum.
  • Seromas tend to be anterior.
  • Haematomas can be anywhere and look like anything.
49
Q

What are the general rules in differentiating peri nephric fluid collections according to shape?

A
  • Lymphoceles are wedge-shaped when small and tend to be thin-walled.
  • Seromas tend to be tubular and follow tissue planes (rarely large).
50
Q

What are the general rules in differentiating peri nephric fluid collections according to internal echoes?

A
  • There are very few echoes except that septations tend to represent a lymphocele.
  • Urinomas are also without echoes but can have thick walls.
  • Seromas are usually septated.
  • Haematomas are variable.
51
Q

What are the general rules in differentiating peri nephric fluid collections clinically?

A
  • Hematomas, urinomas and seromas are lesions identified in the first couple of weeks.
  • Haematomas and urinomas are painful, unlike seromas and lymphoceles.
  • Hydronephrosis is associated with lymphoceles and urinomas
52
Q

What are some vascular complications of renal transplant?

A
  • RAS
  • Renal artery thrombosis
  • Renal vein thrombosis
  • AV fistula/arterial pseudoaneurysm
53
Q

Is ultrasound useful in renal allograft vascular complictions?

A
  • important as it is an area where ultrasound can be of significant benefit.
  • It has already been mentioned that the vessels of the transplant kidney are very accessible.
54
Q

What is the criteria for RAS in the renal allograft?

A

The site of anastomosis is most important to examine.
should be suspected in cases of severe hypertension refractory to medical therapy
1. Color aliasing at the stenotic segment
2. Distal turbulent flow
3. Peak systolic velocity > 250 cm/sec
4. Velocity gradient between the renal artery and external iliac artery greater than 1.8:1

55
Q

What does renal artery thrombosis suggest in the setting of renal transplant?

A
  • This is uncommon
  • It places the kidney at risk of overall demise.
  • It is often a complication of rejection.
  • Rejection must be suspected when there is an identified occlusion of the renal artery
56
Q

What is of particular importance when assessing the renal allograft in bmode?

A

• peri-nephric space is of particular importance to exclude the presence of peri-nephric collections.

57
Q

What is considered normal diastolic flow in the renal allograft?

A

• Normal diastolic flow is around half of the PSV.

58
Q

What extra renal arteries are examined in a renal allograft study and why?

A

arteries from which the allografts arteries are arising since patients with end stage renal failure are more prone to develop peripheral vascular disease.

59
Q

What are the normal spectral traces of a renal allograft?

A

Intrarenal spectral traces of upper, middle, and lower poles show a resistive index of less than 0.8 and continuous flow throughout diastole.
The main renal artery shows continuous flow with peak velocities less than 200 cm/sec.

60
Q

What are the difficulties that are faced when imaging a renal artery stent and how are these overcome?

A

it is an echogenic attenuative structure.
This makes visualisation across it, very difficult.
It can also mean that the stent will appear to be morphologically reduce while it isn’t.
they tend to be located at the origin of the vessel which is often at 90 degrees to the transducer.
Obtaining a frequency shift at a reasonable angle can be therefore very difficult.
The solution is thus to optimise your system to account for these issues. Amplitude Doppler is especially important. Use lower frequencies and sensitive colour settings. Use windows such as the lateral windows to optimise the angle.

61
Q

How do you calculate acceleration time?

A

Change in velocity/change in time

62
Q

How long after surgery will a urinary leak appear?

A

Up to three weeks

63
Q

A urinary leak will present with what pathology on diagnostic imaging?

A

Urinoma

64
Q

What is the significance of hydronephrosis?

A

Around 2/3 of kidneys where the dilation includes the pelvis and the calyces will be obstructed

65
Q

How successful is ultrasound at showing the site of urinary obstruction.?

A

Ultrasound does not do well at showing the level of obstruction. It is successful in only 13-15% of occasions where this occurs.

Son5025 Vasc (15 decks)

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