Renal Arteries Flashcards
Renal Arteries anatomy in terms of location? Think left and right? 3
- From the aorta just distal to the RMA
- RRA comes off anteriolateral aorta and passes posterior IVC
- LRA comes of lateral and posterolateral aorta
20% of kidneys supplied by what?
Duplicated or accessory arteries
Renal arteries divided how in the renal pelvis?
Vessels that lie anterior and posterior to the renal pelvis, each supplying a different segment
How many segments of the renal arteries are there?
- 4 anterior segmental arteries
- 1 posterior segmental arteries
Segmental arteries branch into what?
Interlobar arteries that reach into the parenchyma
Segmental arteries terminate in what?
Arcuate arteries that lie at the cortico- medullary junction
Interlobar arteries branch off what?
Arcuate arteries in the peripheral cortex
What doe we do with the kidney before evaluating vessels? 2
- Assess kidney size and morphology
- Normal is 9-13 cm, can be as small as 8cm
What is the usually approach for interrogation of the renal arteries? 2
- Transverse, anterior, midline
- RRA can usually folow this way, but a coronal approach may be needed to follow the LRA
What factors contribute to the success of the renal artery exam? 3
- Artery depth
- Respiration
- Abdominal gas
What is usually done for renal artery exams in terms of patient prep?
12 hour fast and scanning in the morning possible to study 90% of patients
In terms of interrogation of the renal arteries, it is important to do what?
Assess the entire length of the vessel to avoid missing lesions
What probe is generally used for Renal artery exams?
2.5-3 MHz probe
LRV passes between the aorta and SMV entering what?
The left side of the IVC
LRV receives which veins?
Left suprarenal and left gonadal vein
Which Renal vein is shorter?
RRV is shorter than the left and extended directly to the hilum
The RRV does not accept what?
No tributaries but it is more common to find accessory veins draining directly into the IVC
Suprarenal (proximal) aortic signal has what kind of flow characteristics?
Low resistance, monophasic waveform because it is feeding a low resistance vascular bed up to this point
What is the velocity of the suprarenal (proximal) artery?
80-100 cm/sec
Distal to the renal arteries what happens to the pattern changes?
Pattern changes to a high resistance multiphasic with a reverse flow component
What are some normal flow characteristics of the renal artery? 3
- Normal low resistance
- Early systolic peak/ compliance peak, may be seen on the upstroke to systole
- 74-127 cm/s
What parts of the renal artery do we assess? (With U/S)
Origin, mid, distal
In the renal artery, what is considered abnormal in terms of velocity and stenosis?
> 180 cm/sec, indicates stenosis >60^
What is the renal artery PSV to Aortic PSV ratio (RAR)?
Normally <3.5
Segmental artery’s have how many branches?
Multiple
What is the doppler waveform of segmental arteries like?
Similar to distal renal artery but with lower velocities
What is the normal segmental artery look like? (Think waveform)
Sharp systolic upstroke and ESP
What does abnormal segmental artery spectral look like?
Delayed AT and rounded peak
Where are Interlobar arteries located?
Between collecting system calyces
In terms of Interlobar arteries, doppler signals are obtained where? 3
- Upper
- Mid
- Lower poles
Where are arcuate and lnterlobular attires located?
Cortical region of the kidney and are called the parenchymal arteries
Where are the renal veins located and what is their normal flow characteristics like? 3
- Near the IVC
- Multiphasic pattern due to proximity to the IVC and heart
- Dismally they have phasic flow, vessel diameter changes with respiration
Stenosis or occlusion of renal artery may cause what?
Ischemia leading to hypertension
Renal artery stenosis is the most common cause of what? 3
- Secondary hypertension
- Chronic renal insufficiency
- End stage renal disease
Renal artery stenosis can cause what kind of damage?
Parenchyma damage
In terms of renal artery stenosis/ occlusion, Colour flow does what?
Locates the arteries and detects flow disturbances which indicates stenosis
In terms of renal artery stenosis/ occlusion, doppler spectral determines what?
Quantifies stenosis severity
Hemodynamically significant stenosis have a >60% diameter reduction
What are some situations where renal artery stasis should be investigated in? 9
- Sudden onset or acceleration of chronic hypertension
- Unexplained renal insufficiency
- Abdominal bruit
- Azotemia - elevation of nitrogen, creatinine and other waste in your blood
- Decreased serum potassium
- Recurrent congestive heart failure
- Pulmonary edema
- Unilateral strophic kidney and discrepancy renal size greater than 1.5 cm
- Hypertensive children
Renal artery stenosis can result from several conditions including what? 9
- Atherosclerosis - Most common (90%) , older population >50
- FMD - usually <40 year olds
- Dissection extending into the renal arterie s
- Aneurysms of the main or segmental arteries
- Aortic coarctation proximal to the renal artery origins
- Arteriovenous fistula
- Arteritis (vasculitis)
- Extrinsic compression of the renal artery and/or vein by tumor/masses
- Radiation
What is the most correctable cause of hypertension?
Renal artery stenosis
What are some things we can do to interprete a renal artery stenosis <60%? 4
- Grayscale may demonstrate atherosclerotic plaque
- COlour flow helps identify disturbed flow and lumen narrowing
- With narrowing <60% it is not yet severe enough to cause a decrease in pressure and flow distal to the lesion
- Post- stenotic turbulence is not present
How do we interpret renal artery stenosis >60%? 4 (What do we see?)
- PSV increases significantly
- Post stenotic turbulence is present
- PSV of >180 cm/sec and renal/aortic ratio (RAR) of >3.5 indicate significant stenosis
- Renal infarcts (hypoechoic ares within the kidney) may be seen
How do we interpret renal artery stenosis >80%? 4 (How does the waveform look like?)
- Systolic upstroke is delayed
- Early system peak (ESP) is lost
- PSV decreases dismally, monophasic (tarsus parvus)
- In the absence of elevated renovascuar resistance diastolic flow will be maintained
How do we interpret renal artery occlusion? 3( how do we confirm it, what is the renal flow like?)
- Confirmed by usuing optimized spectral, colour, and power doppler to demonstrate the abscence of flow
- Non- visualization of the main renal artery
- Absent or very low flow and dampened renal flow (hypoperfusion)
In terms of a renal artery occlusion, the kidney is supplied by adrenal and ureteral collaterals, what is seen in the renal medulla and cortex?
Low velocity doppler signals
In terms of a renal artery occlusion, What is the PSV of the cortex and what is the renal length?
PSV in the cortex is usually <10cm/sec and renal length is often less than 9cm
In terms of interpretation of renal artery occlusion, we should avoid a false- positive diagnose of renal artery occlusion when we see what?
When there is poor visualization of the kidney and the artery
In terms of intrinsic parenchymal dysfunction, we need to do what?
Obtain spectral waveforms throughout the parenchymal vessels in the media and cortex of the kidney
What is the normal intrinsic parenchymal dysfunction waveform?
Low resistance
In terms of intrinsic parenchymal dysfunction, what is the abnormal waveform?
High resistance waveform, associated with parenchymal dysfunction/ medical renal disease
In terms of abnormal intrinsic parenchymal dysfunction, the degree of Reno vascular resistance can be determined by what?
RI
RI of what is indicative of medical renal disease?
> 0.8
Urinary tract obstruction, acute and chronic parenchymal disease can cause what to happen in the kidney?
Increased resistance within the kidney
What is the most common outcome from renal vein thrombosis?
Primary renal disease
RV thrombosis is also caused by what? 8 (Besides the main cause)
Other conditions such as
1. Hypercoaguable states
2. Renal
3. IVC
4. IVC or ovarian tumor thrombus
5. Abdominal surgery
6. Surgery
7. Trauma
8. Dehydration
Renal veins may be blocked by what? 2
Intraluminal thrombus or by extrinsic compression
Renal vein thrombosis causes what? (2, disease and what it leads to)
Parenchymal disease and leads to renal failure
What does renal veins look like normally with u/s? 2
- Anechoic lumen
- Respirophasicity throughout all visualized segments
What does abnormal renal veins look like? 3
- Intraluminal echoes
- Continuous, non phasic, low velocity flow seen proximal to thromboses Venous segments
- Minimally phasic flow is seen dismally if the thromboses segment has recanalized or if collaterals have developed
If the renal veins are severely damaged by thrombosis, what can be seen happen to the renals? 2
- Renal atrophy may be seen
- May have increased echogenicity compared to the normal contra lateral organ
Chronic RV thrombosis presents as what? (asymptomatic/ symptomatic or diseases)
Asymptomatic or presents with nephrotic syndrome (hydro Proteinuria) or hematuria
How does Acute RV thrombosis present in terms of S/S? 3
- Pain and hematuria
- Vein is often dilated and respirophasic flow is absent
- Kidney is usually enlarged with a variable echogenic pattern throughout the medulla and cortex
What is nutcracker syndrome? 2 (what it looks like, and what is the spectral look like?)
- Left renal vein is compressed by the mesentery or SMA
- High velocity signal associated with a colour bruit may be seen in the vein as it crosses anterior to the aorta
In terms of renal stents, lesions occur most frequently where?
In the proximal renal artery and are amenable to Percutaneous transluminal angioplasty (PTA) with or without stenting
What does contrast arteriography provide?
Anatomical information
Contrast arteriography will not be able to determine what in hypertensive patients?
Identify the functional significance of renal artery disease in hypertension patients
Contrast arteriography does not provide what?
Hemodynamics information
Is contrast arteriography invasive?
Invasive
What does MRA stand for?
Magnetic resonance angiography
What is CTA?
Computed tomography angiography
How effective is MRA and CTA?
Less invasive than arteriography with excellent specificity and sensitity
What is the cost of MRA and CTA?
Relatively expensive and require injection of IV contrast
CTA iodinated contrast agent risks?
May be nephrotoxic and is unsuitable for use in patients with renal insufficiency
Benefits of duplex u/s in terms of renal testing 4
- Widely available
- Low cost without the risk of ionizing radiation or use of nephrotoxic contrast
- Noninvasive
- Painless
Disadvantage of duplex sonography for renal testing?
80%-90% effective for identifying renal artery stenosis and quantifying its hemodynamic significance
What is the standard treatment for chronic renal failure?
Renal transplant
What is an allograft?
Any tissue transplanted from one human to another. Therefore, in terms of renal transplant it is a renal allograft
How do we get renal transplants organs?
Harvested from a living, related donor or brain dead donor (cadeveric donor)
Where is a renal transplant placed?
In the iliac fossa (right) between the peritoneum and the iliacus muscle
What happens to the native kidney and ureters with renal transplants?
Left in place
In terms of long term dialysis patients, native kidneys are prone to what
Cysts and neoplasms
Allograft ureter is passed obliquely through what during renal transplant?
Through the muscular layer of the bladder forming a non-refluxing UV junction
Allograft veins are anastomosed how?
End to side with iliac vein
Allograft arteries can be attached how?
In a variety of ways
Superficial location of the transplant kidney allows for what?
Excellent visualization
What is the allograft appearance during u/s?
Similar to native kidney
What are some considerations when evaluating allograft syndrome? 3 (what does it look like)
- Cortex may appear more echogenic due to lack of attenuating structures over the kidney
- Usually enlarges over a period of months following transplant (up to 30%) and should not be mistaken for rejection
- Slight dilatation of the collecting system (hydronephrosis)
Allograft appearence baseline studies should be done when?
Within 72 hours
What is the renal 2D transplant protocol? 5
- SAG: length measurement, medial and lateral views
- Transverse: Upper, mid and lower poles with AP measurement
- Image the venous arterial anastomosis sites
- Survey theperinephric space for any fluid collections
- SAG and TRANS images of the bladder, possibly pre and post void volume
What is the color and spectral protocol for external iliac artery?
Colour and angle corrected spectral waveforms proximal and distal to the Rena artery anastomosis
What is the colour and spectral protocol for main renal artery? 4
- Colour from the anastomosis to the hilum
- Spectral at the anastomosis and proximal, mid and distal renal artery with PSVs
- If Possibly the RI of renal artery to iliac artery ratio
- Repeat if multiple renal arteries
What does the normal colour and spectral look like for main renal artery? 2
- Low resistance
- RI <0.7 and sharp systolic upstroke
What is the colour and spectral external iliac vein protocol?
Colour and spectral or proximal, mid, distal, and main renal vein anastomosis
What is the colour and spectral renal vein protocol? 2
- Colour fro the EIV to the hilum
- Spectral doppler at anastomosis and distal to the anastomosis
What is the colour and spectral protocol for the parenchymal/hilar arteries and veins?
Spectral from the upper, mid, and lower poles
Why do we need to put colour of the entire kidney with renal transplant protocol?
To provide a global assessment of renal perfusion and to look for any vascular abnormalities
One of the most common causes of graft loss is what?
Rejection of renal transplants
What is rejection of a renal transplant due to?
Attack by the immune system on the allograft
Should rejection of allografts be diagnosed sonographically?
No, unless rejection several related abnormalities are present (such as biopsy)
What are three signs of rejection of a graft?
- Sudden cessation of urine output (anuria)
- Decreased urine output
- Increased serum creatinine
What might mimic signs of rejection?
Cyclosporine toxicity
What kind of waveforms point in the direction of rejection?
High resistance doppler waveforms with minimal to absent diastolic flow. RI of >0.7 is abnormal
What is acute tubular necrosis in terms of renal transplant complications?
Post surgical response resulting from ischemia
Are doppler studies for acute tubular necrosis usually altered?
No
Do we see hydronephrosis with Renal transplant complications?2
- Mild hydronephrosis may be normal
- True Hydronephrosis may develop secondary to uteral stricture from post surgical scarring, bladder distention or compression from surrounding fluid collections
What are peri-graft fluids?
Collections commonly seen post operatively
What is seen with peri-graft fluid?4
- Seromas
- Hematomas
- Abscesses
- Urinomas
What does colour doppler prove with peri-graft fluid?
If there is active bleeding into these collecitons
Where does pseudoaneurysms occur with rental transplant complications?
In renal parenchyma during biopsy
In terms of pseudoaneurysms and renal transplant complications, what is seen visible from the neck?
High velocity jet
Pseudoaneurysms might occur where?
At the arterial anastomosis site
How does AV fistulas occur with in terms of renal vasculature?
Occur from biopsy trauma, usually asymptomatic
In terms of renal transplant complications, AV fistulas might be associated with what?
Sustained hypertension
In terms of AV fistulas and renal transplant complications, what does av fistulas look like with colour Doppler? Why?
A bright spot in the renal parenchyma due to disturbed flow
What does high velocity flow with AV fistulas indicate? (what does it show)
The feeder artery with a visible colour bruit
What are the chances of seeing venous/arterial thrombosis as a renal transplant complicaiton?
<1%, we’d usually see it immediately post operatively
In terms of renal transplant complications, What are venous/ arterial thrombosis s/s in 2D? 3
- Enlarged kidneys
- Distended renal vein
- Absent flow signals
What is the most common vascular complication of renal transplant complication?
Arterial stenosis
Post-op arterial stenosis in terms of renal transplant complication happens where?Why?
Stenosis occuring post-op usually at the anastomosis and due to a surgical issue
Older transplants have long segment stenosis due to what?
Scarring and hyperplasia
In terms of renal transplant complication and arterial stenosis, what do we see with doppler?
Doppler shows increased velocity in the stenotic segment, post-stenotic turbulence and distal dampening with severe stenosis
What is hemodialysis?
Removal of certain elements from the blood through a semi-permeable membrane while being circulated outside the body
What is necessary with end stage renal disease?
Hemodialysis
Hemodialysis requires what?
High flow in an easily accessed vessel that can tolerate multiple punctures
AV fistulas are surgically created by doing what? Why do we do this?
Connecting an artery and vein together, to accomplish a high flow situation (blood flows from high pressure arteries to low pressure veins)
Where are AV fistulas created surgically?
As distal as possible in the non-dominant arm
Why is an autogenous AVF is preferred?
Due to its superior patency rate and lower rate of complications compared to prosthetic grafts
How common is brescia-cimino fistulas? What does it involve?
Common and involves mobilizing the distal cephalic vein at the wrist and anastomosing it to the distal radial artery end to side
Why is a brescia-cimino fistula considered? 3
- Due to its distal location
- Need for minimal dissection
- Vessel mobilization
What is a AV graft or AVG? And why do we do them?2
- Connects an artery to vein using a prosthetic graft or a vein as a conduit
- Sometimes an AVF is not possible and a graft may be surgically inserted
What are the most common abnormalities with Renal dialysis fistulas and grafts? 8
- Venous outflow obstruction
- Venous anastomosis stenosis (50-90%)
- Pseudoaneurysm
- Diffuse aneurismal dilation
- Hematoma
- Peri-graft abscess
- Intimal flaps
- Arterial anastomotic stenosis
What are methods of evaluation for hemodialysis grafts and AVF?2
- Duplex ultrasound
- Arteriography
In terms of renal dialysis fistulas and grafts, what are indications for doppler ultrasound?2
- Surveillance imaging has been shown to improve patency and durability
- Assessment for pseudoaneurysm, graft degeneration, thrombosis, hematomas and arterial inflow stenosis
Thrombosis of the graft is the most common cause of failure when?
First month
What are indications for doppler ultrasound? (In terms of renal dialysis fistulas and grafts)8
- Pulsatile mass
- Decreased bruit or thrill in the access conduit
- Difficult cannulation
- Elevated recirculation time
- Elevated venous pressure during dialysis
- Arm edema and/or swelling - high incidence of subclavian vein thrombosis
- Infection
- Arterial steal symptoms
What kind of probe do we need for a duplex scan for hemodialysis grafts and AVF? and what do we need to do for success?3
- 10-12 MHz transducer with high flow settings,
- Decreased colour gain to minimize tissue bruit
- Patient in supine position
In terms of hemodialysis grafts and AVF Duplex tests, what do we need to sample? 6
- PSV at native artery proximal
- Arterial anastomosis
- Graft
- Venous anastomosis
- Venous outflow
- AVF sample 2-3 sites distal to arterial anastomosis
In terms of hemodialysis grafts and AVF, peak systolic velocity ratios (V2/V1) are more frequently used to determine what?
The severity of stenosis than PSVs
What does a normal Hemodialysis graft and AVF look like in 2D and colour?2
- No decreased lumen
- Colour fills the vessel lumen from wall to wall
What does a normal Hemodialysis graft and AVF look like in terms of waveforms?
High flow states, seen as low resistance with increased PSV and EDV
What does a normal Hemodialysis graft and AVF look like in terms of Depth?
<5mm from the skin surface is required for successful access for dialysis
What does a abnormal hemodialysis graft and AVF look like in terms of 2D and colour?2
- Decreased lumen
- Colour jet, increased velocities and post-stenotic turbulence
In terms of hemodialysis grafts and AVF, What does decreased venous spontaneity and respirophasicity suggest?
Obstruction in outflow vein
In terms of hemodialysis grafts and AVF, What do we need to evaluate in terms of waveform? 3
Assess SCV and Internal jugular veins for:
1. Spontaneity
2. Phasicity
3. Pulsatility
In terms of hemodialysis grafts and AVF, what does volume flow look like for a suboptimal graft and fistula performance?
- Suboptimal graft: <800mL/min
- Suboptimal fistula <500mL/min
In terms of stents what is the number and locations of the stents?
Variable
Proximal renal artery stents are best visualized from which window?
Transverse
In terms of renal stents, slight velocity increase is expected due to what?
Reduction in arterial compliance
Increased velocity may be seen at the distal end of the stent when?
If the stent exceeds the diameter of the native artery
In terms of renal stents, If turbulence is seen with dampening of the distal waveform, what should be suspected?
Significant stenosis
