The document discusses renal Doppler anatomy, emphasizing the anatomical positions and imaging techniques for assessing renal arteries and their branches. It details the criteria for diagnosing renal artery stenosis, including Doppler waveforms, peak systolic velocities, and intrarenal waveform assessments, as well as the impact of variations in renal perfusion and resistance index (RI) in conditions like diabetic nephropathy and acute kidney injury. Additionally, it covers conditions such as renal vein thrombosis and renal artery aneurysms, highlighting the role of ultrasound and color Doppler in evaluating kidney diseases.

1. RENAL DOPPLER

2. ANATOMY
• at the level of the superior border of the second lumbar vertebra.
• 1–2 cm below the superior mesenteric artery origin.
• Right artery-originates from the anterolateral aspect of the aorta.
• immediately turns posteriorly to course beneath the inferior vena
cava.
• Right renal artery is not only deep in the abdomen- flank approach is
better.

3. • Left renal artery originate from the posterolateral surface of the aorta.
• courses posteriorly the surface of the aorta and over the psoas muscle.
• mistaking the origin of the inferior mesenteric artery (IMA) for that
of the left RA.
• the IMA tends to have a high resistance spectral waveform.
• IMA also originates much lower along the aorta than the left RA

4. “banana peel” view
• the transducer is oriented longitudinally.
• The aorta is located, and the transducer is moved in an anterior-to-
posterior direction until the RA is identified arising from it.
• coursing towards the transducer.

6. • The main RA divides at the hilum, either within or outside the kidney,
into anterior and posterior branches.
• further divide into segmental and then interlobar arteries.
• The interlobar arteries further divide into a network of arcuate
arteries.
• run at the corticomedullary junction and give off the cortical
(interlobular) branches.

8. PROTOCOL
• longitudinal survey of the abdominal aorta from the celiac artery to
the iliac bifurcation.
• Gray-scale evaluation is important to assess for irregular plaque and
ostial lesions.
• The presence of significant atherosclerotic plaque should increase the
suspicion for possible ostial renal artery disease.
• begin at the celiac axis or the superior mesenteric artery, move
slightly caudad along the aorta until the origin of each renal artery is
seen

9. • locate the origin of the renal arteries on transverse images of the aorta
using an anterior transducer approach.
• The right renal artery is often easier to identify than the left with this
approach.
• The left renal artery may be better seen by positioning the patient in a
right lateral decubitus position and scanning from a left posterolateral
transducer approach.
• Each renal artery should be examined with color flow imaging from its
origin to the hilum of the kidney, including the main hilar branches.

10. • obtain PSV measurements from the origin, proximal, mid, and distal
segments of each renal artery.
• A small sample volume (1.5-2.0mm), and an angle of insonation of 60
degrees or less are used.
• Waveforms are also obtained from the segmental arteries in the
upper, mid, and lower poles of each kidney.
• determine the PSV, acceleration time or index, and the resistivity
index (RI).

11. NORMAL FINDINGS
• The normal PSV range in adult renal arteries is 60 to 100cm/sec.
• Normal renal artery waveforms demonstrate a rapid systolic upstroke
with persistent forward flow in diastole.
• a complete renal artery Doppler examination can be performed in as
little as 20minutes.

12. RENAL ARTERY STENOSIS
• It is the most common potentially reversible and curable cause of secondary
hypertension and renal failure.
• most commonly caused by either fibromuscular dysplasia or
atherosclerosis.
• associated with hypertension, renal insufficiency (ischemic nephropathy)
or both.
• arteritis, dissection and neurofibromatosis.

13. • Arteritis, dissection and neurofibromatosis.
• atherosclerotic disease- mainly affects the orifice and proximal
portion of the RA.
• FMD- involves mid to distal portion.

14. DOPPLER CRITERIA FOR RENAL ARTERY
STENOSIS
• PROXIMAL CRITERIA-
• direct signs obtained at the site of the stenosis.
• Four criteria are used to diagnose significant proximal stenosis.
• Velocities higher than 180 cm/s suggest the presence of a stenosis of
more than 60% .

15. • The second criterion is the comparison of PSV values obtained in the
prerenal abdominal aorta with those measured in the Ras.
• renal/aortic ratio (RAR)
• In normal conditions, RAR is lower than 3.5.
• The third criterion is identification of RAs with no detectable Doppler
signal, a finding than indicates occlusion.

18. • The fourth criterion is the visualization of color artifacts such as
aliasing at the site of the stenosis.
• the presence of turbulence at Doppler evaluation indicating the
presence of a significant stenosis upstream.

19. DISTAL CRITERIA
• oss of early systolic peak;
• acceleration index (AI) lower than 3 m/s2
;
• acceleration time (AT) < 0.07 s;
• a difference between the kidneys in RI (>0.05–0.07)

20. Intrarenal Waveform Assessment
• indirect diagnosis of renal artery stenosis through the detection of
damped Doppler waveforms in segmental or interlobar arteries within
the kidney.
• renal artery stenosis can cause pulsus tardus and parvus (“tardus
parvus”) changes in intrarenal arterial flow signals.
• intrarenal waveform findings are more accurate for high-grade renal
artery stenoses exceeding 70% diameter reduction.

21. • some patients do not have appreciable waveform damping.
• This is because the shape of intrarenal arterial waveforms is affected by
multiple factors.
• Patient with generalized arterial stiffness and/or high resistance in the
microvasculature from parenchymal renal disease, the damping effects of
a main renal artery stenosis may be obliterated.
• damped intrarenal waveforms can occasionally be seen in the absence of
significant renal artery stenosis in patients with aortic stenosis or aortic
occlusion

22. • downstream effects of renal artery stenosis can be diagnosed merely
by visual inspection of the shape of the segmental or interlobar
Doppler waveforms.
• the initial systolic peak is absent
• (OR)
• the systolic peak is grossly rounded in patients with severe ipsilateral
stenosis

23. • flow at the renal hilum- damped and show a slow rise to the peak
systole.
• This phenomenon has been called the “tardus–parvus” effect.

25. POST TREATMENT

27. DOPPLER WAVEFORM ABNORMALITIES IN
NONVASCULAR RENAL DISEASE
• Flow resistance within the renal parenchyma may be increased by a
variety of pathologic processes like
• urinary tract obstruction
• acute and chronic parenchymal disorder
• glomerulosclerosis, acute tubular necrosis, and pyelonephritis.

28. • All of these conditions are associated with increased flow resistance
in the microvasculature of the kidney.
• causes the Doppler waveforms to exhibit increased pulsatility.
• This may be evident on visual inspection of waveforms or through
pulsatility measures such as the RI.

29. RI & DIABETIC NEPHROPATHY
• Obtained from the Doppler spectrum of intrarenal segmental and
interlobar arteries.
• Normal RRI values in adults are in the range of 0.47–0.70 with a
difference between two kidneys less than 5–8 % .
• diabetic patients with normal renal function and normo-albuminuria
showed RRI values significantly higher compared to non-diabetic
controls without kidney disease.

30. • identification of morphologic and hemodynamic changes in the
earlier stages of diabetic nephropathy.
• RI significantly correlates with the degree of proteinuria resulting
higher in patients with macroalbuminuria.
• RI>0.7 is an independent predictor of the risk of worsening renal
function

31. RI & CKD
• RI has shown to be related with glomerulosclerosis, arteriolosclerosis
and tubulointerstitial lesions more than others morphologic
parameters like renal length and cortex area.
• Patients with High-Normal RRI showed good response to steroid
therapy [high normal RRI (0.65 ≤ RI < 0.7)].
• In mild to moderate renal dysfunction, RRI predicts CKD progression
and poor outcome.

32. • In vasculitis such LES, Wegener Granulomatosis and PAN, RRI shows
significant correlation with creatinine level and presence of
interstitial disease.
• normal RRI value is considered a good prognostic factor.
• Ultrasound may be a useful tool to identify the degree of disease
progression and secondary response to immunological and
antihypertensive therapy.

33. RI & AKI
• RI monitors renal perfusion in critically ill patients and vasoactive
agents’ impact on renal circulation.
• In acute renal injury AKIN stage 3 or RIFLE class F, RRI usually
exceed 0.7.
• a threshold of 0.75 is reported as optimal in recognizing between
renal and prerenal disease.

34. • in prerenal ARF, RRI values lower than 0.7 are related to a good
recovery after fluid rehydration.
• RRI >0.7 suggest a developing ischemic ATN and worse prognosis.

35. Role of RI in evaluating AKI-
Evaluating renal perfusion
Predicting renal response to vasoactive agents.
Recognize between pre-renal and renal disease.
Predicting AKI onset and recovery in septic shock patients.
Predicting renal obstruction.

36. RI & RENAL ALLOGRAFT
• Chronic allograft nephropathy (CAN) remains the leading cause of poor
graft outcome.
• interstitial fibrosis and tubular atrophy.
• result of several different immunologic and non-immunologic processes..
• The main clinical aspects of CAN include slow but variable loss of
function, often in combination with proteinuria and hypertension.

37. • Color Doppler ultrasonography and RRI are valid tools in evaluating
vascular and not vascular graft compartments and its evolution in the
follow-up.
• a direct correlation between acute tubular necrosis and RRI, when
biopsy was performed because of graft dysfunction.
• RRI >0.75 at the 3 month by the time of transplantation has been
associated with increased risk of new onset diabetes after
transplantation (NODAT).

38. Renal vein thrombosis
• bland or tumor thrombus.
• Comprises partial occlusion of the vein versus complete obstruction.
• Clinically RVT presents with hematuria or signs of renal failure such
as rising creatinine or anuria.
• an increase in renal size and change in echogenicity is often observed
due to associated venous congestion.
• Spectral Doppler demonstrates a reversal of diastolic flow in the main
renal artery.

39. • Changes in echogenicity may include the following:
• (1) hypoechoic cortex with decreased corticomedullary
differentiation,
• (2) hyperechoic cortex with preservation of corticomedullary
differentiation
• (3) mottled heterogeneity accompanied by the loss of normal
intrarenal architecture

40. • the conclusive diagnosis of renal vein thrombosis depends on the
direct identification of thrombus in the renal vein.
• With acute thrombosis, the renal vein is invariably enlarged, and
Doppler signals are absent.
• A small trickle of flow may be present around the clot, and this may
produce low velocity, continuous Doppler signals.

43. RENAL ARTERY ANEURYSM
• mean of 4.5 to 5mm at the ostium.
• Most renal artery aneurysms do not exceed 2cm in diameter and are usually
discovered incidentally.
• Most are saccular and noncalcified and tend to occur at the bifurcation of
the main renal artery.
• Renal artery aneurysms are subdivided into two categories: extrarenal and
intrarenal.

44. EXTRA RENAL
• caused by atherosclerosis and
FMD.
• the main renal artery may
demonstrate a “string of beads”
appearance on power Doppler.
• may show long segmental
narrowing of the proximal, mid
or distal aspects of the main
renal artery.
INTRARENAL
• generally very small and
multiple.
• Seen in pts with PAN.
• Microaneurysms range in size
from 1 to 12mm.

47. CONCLUSION
• Ultrasound imaging and Color Doppler permit to define
morphological and functional parameters to reach a better prognostic
evaluation among kidney diseases.
• the usefulness of RRI as a prognostic marker has been clearly and
successful highlighted in the follow-up of diabetic and non-diabetic
nephropathies, acute kidney injury and kidney transplantation.

48. THANK YOU