Doppler ultrasound of the kidneys 1

Doppler ultrasound of the kidneys

Dr. Muhammad Bin Zulfiqar

PGR FCPS SHL

Doppler US of the kidneys

• Normal anatomy of the kidney

• Normal US of the kidney

• Normal Doppler US of the kidney

• Indications of renal Doppler US

Normal anatomy of the kidney

Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41.

Renal parenchyma: cortex & medullary pyramids

Renal sinus: arteries, veins, lymphatics, collecting system, & fat

Renal hilum: Concave, in continuity with renal sinus

Anatomy of renal arteries

RRA: Usually passes posterior to inferior vena cava

LRA: Usually courses posterior to left renal vein

Multiple renal arteries in 25% (inferior polar artery from aorta)

Arterial blood supply to the Kidney

Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004.

Segmental arteryApical, upper, middle, lower, posterior

Interlobular arteryBetween renal pyramids

Glomerular arteriole

Main renal artery

Arcuate arteryBetween cortex & medulla

Left renal vein

• Longer than right renal vein

• Averages 85 mm in length (range: 60 – 110 mm)

• Joined by adrenal, gonadal, lumbar, & hemiazygousveins before crossing the aorta

• Different types: Pre-aortic 80 – 95% Retro-aortic 2 – 3%Circum-aortic 7 – 9%

Sidhu R et al. Semin Ultrasound CT MRI 2009 ; 30 : 271 – 288.

Variants of left renal vein Retro-aortic LRV

Incidence: 2 – 3%

Circum-aortic LRV

Incidence: 7 – 9%


Left-sided IVC

Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004.

Normal anatomy of IVC Anomalous left-sided IVC

Persistence of embryological AV

Gray scale imaging first

• Kidneys Maximum renal length Echogenicity of renal cortexThickness of renal cortexMasses – hydronephrosis – renal calculi

• Aorta Plaque – thrombus – dissection – aneurysm

• Adrenal glands

Normal kidneyLongitudinal section Cross section

Rumack CM et al. Diagnostic Ultrasound. Elsevier-Mosby, St. Louis, USA, 3rd edition, 2005.

Renal capsule: echogenic line

Renal parenchyma: outer cortex & inner medulla pyramid

Central sinus complex: high echogenicity (vessels, fat, fibrous tissue)

Renal dimensions

• Length of normal kidney: 9 – 14 cm

Right kidney smaller than left kidney

• Discrepancy > 2 cm between two kidneys:

Considered significant & needs further evaluation

• Renal length between 8 – 9 cm

Correlated to patient’s phenotype particularly height

• Renal length < 8 cm definitely reduced

Should be attributed to chronic renal failure

Fiorini F et al. J Ultrasound 2007 ; 10 : 161 – 167.

Measurement of parenchymal & cortical thickness

Cortical thickness: Normal 8 – 10 mm

Parenchymal thickness: Normal 14 – 18 mm

Tuma J et al. European course book: Genitourinary ultrasound.

European Foundation of Societies of Ultrasound in Medicine & Biology.

Renal volume

Length: 9 – 14 cm (longitudinal section) Width: 4 – 6 cm (cross section) Depth: 4 – 6 cm (cross section)

Ellipsoid formula: length . width . thickness . π/6

Derchi LE et al. Acad Radiol 1994 ; 1 : 100 – 105.


Adjusted to BMI

(V / BMI) . 25

Appropriate renal volume

231 ± 50 ml

Classification of renal parenchymal echogenicity

4 types based of US appearance

Hypoechoic compared to liver

Isoechoic compared to liver

Hyperechoic compared to liver

Isoechoic to renal sinus

Normal

Normal

Pathological

Pathological

Grade 0

Grade I

Grade II

Grade III

Kidney parenchyma compared to liver parenchyma

Hypoechoic Isoechoic

Hyperechoic


Congenital normal variants of kidney

• Dromedary hump

• Persistent fetal lobulation

• Prominent column of Bertin

• Junctional parenchymal defect

• Hypoechoic renal sinus


Dromedary humpCommon renal variation


Focal bulge on lateral border of left kidney

Result from adaptation of renal surface to adjacent spleen

Easily differentiated from renal mass by Doppler

Persistent fetal lobulation


Renal surface indentations between pyramids

May be single or multiple

Prominent column of Bertin (PCB)Mistaken for intrarenal tumor


Continuity with renal cortex

Similar echo pattern as renal parenchyma

Similar vascular pattern by color & power Doppler

Junctional fusion defect


Mistaken for cortical scar or angiomyolipoma

Continuity with central sinus

by echogenic line

“inter-renicular septum”

Triangular hyperechoic structure

Antero-superior or postero-inferior

surface of kidney

Abdominal aorta

• Normal abdominal aorta 1.5 – 2.5 cm

• Ectatic aorta 2.5 – 3 cm

• Aortic aneurysm > 3 cm

• Annual growth of aneurysms 0.33 cm/year between 4 & 5.5 cm

* Bhatt S et al. Ultrasound Clin 2008 ; 3 : 83 – 91.

Cross-section at adrenal glands Compared to seagull, Y, or V letter

Y-shaped structures lying antero-medial to kidneys

Composed of body & medial & lateral “wing” or “limb”

Tuma J et al. European course book: Genitourinary ultrasound.

European Foundation of Societies of Ultrasound in Medicine & Biology, 2011.

US of normal adrenal glandsDocumented in 1980 1

1 Dietrich CF et al. Endoscopy 1997 ; 29 : 859 – 864.2 Jenssen C et al. Ultraschall Med 2010 ; 31: 228 – 250.

With modern equipment (high-resolution) & good trainingUS can image right gland in 99% & left gland in 70%1

Transcostal scan in LLDBetween RLL, IVC & diaphragm

Right adrenal gland Left adrenal gland

Transverse scan of epigastriumDorsal to pancreatic tail & SV

Normal adrenal gland / Inverted Y-shape

Hypoechoic right adrenal gland

Horizontally inverted Y-shape

Coronal scan of right upper abdomen through MAL

Wan YL. J Med Ultrasound 2007 ;15 : 213 – 227.

Technical points

• Fasting for at least 6 hours before the exam

• Duration of the examination: 30 – 45 min

• Rare failure: Non-cooperant patient – Gas

• Intestinal preparation: not necessary

Operator-dependent technique

Slow learning curve

Most complex & difficult Doppler examination1

Sites for pulsed Doppler of renal arteries

Aorta Ostium of main renal artery Trunk of main renal artery Hilum of kidney Upper pole of kidney Middle pole of kidney Lower pole of kidney

Transverse scan with probe angulationsMain renal arteries

Schäberle W. Ultrasonography in vascular diagnosis. Springer-Verlag, Berlin, 2nd edition, 2011.

Norma right renal artery

Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475.

Transverse gray scale image

Right main renal artery

Transverse color Doppler image

Right main renal artery

Gray scale alone without color DopplerPatients with difficulty to hold breath


Entire RRA well visualizedColor flash artifact from patient motion may obscure visualization

Better spatial resolution & and faster frame rate

Gray scale image

Norma left renal artery

Gray scale image Color Doppler image


Proximal main left renal artery Proximal main left renal artery

‘‘banana peel’’ or “Isikoff” view

Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475.Isikoff MB et al. Am J Roentgenol 1980 ; 134 : 1177 – 1179.

Origins of right & left renal arteries

Gray scale image

Origins of right & left renal arteries

Color Doppler image

Longitudinal transhepatic view in Left lateral decubitus

Normal right renal artery

Coronal images of IVC


RRA is the only vessel to course laterally under the IVC

Often slightly indents the IVC

Two renal arteries or early branching?

Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412.

Longitudinal view of IVC

Two right renal arteries

Transverse view of aorta

Early branching of RRA

Longitudinal scan in left lateral decubitus

Multiple renal arteries (25%)


Two left renal arteries


PSV: 90 cm/sec

Dominant left renal artery

PSV: 60 cm/sec

Accessory left renal artery

Axial scan in left lateral decubitusUsing right kidney as acoustic window

Right main renal artery & vein

Color Doppler USSchematic drawing

Meola M et al. J Ultrasound 2008 ; 11 : 55 – 73.

Axial scan in right lateral decubitus

Using left kidney as acoustic windowSchematic drawing

Left main renal artery & vein

Color Doppler US

Zubarev AV. Eur Radiol 2001 ; 11 : 1902 – 1915.

Pre caval right renal artery

Pre-aortic left renal vein (80 – 95%)


Reduction in diameter in pre-aortic segment to IVC

with physiologic acceleration

Left renal vein variants



Retro-aortic LRV (2 – 3%) Circum-aortic LRV (7 – 9%)

Pre & retro-aortic LRV

Color Doppler of RRV & retro-hepatic IVC


Righ renal vein Inferior vena cava

Pulsed Doppler of renal veins


Right renal vein

Resembles pulsed Doppler of IVC

Triphasic waveform

Left renal vein

Little modulation

Wall artifact due to systolic peak

Limits in visualization of main renal arteries

•Obesity•Overlying bowel gas•Dyspnea•Shadowing from arterial calcifications•Cardiac arrhythmias•Poor angle of Doppler insonation•Accessory renal arteries (small size)


Expert sonographers detect 80 – 90% of main RACEUS improves success rate to 95%

Angle of insonation

Difficulty in case of tortuous or curved renal artery

Correct angle Incorrect angle

Schäberle W. Ultrasonography in vascular diagnosis.

Springer-Verlag, Berlin Heidelberg, 2nd edition, 2011.

Adjustment of Doppler controlLow flow settings

• Lowest pulse repetition frequency without aliasing

• Small color box

• Greatest gain without background noise

• Lowest wall filter

• High color priority

Normal segmental & interlobar renal arteries

Normal segmental renal arteries (long arrows)

Color Doppler image of the kidney


Normal inter-lobar renal arteries (short arrows)

Study of intra-renal arteriesPerfusion study / Low PRF


Cortical perfusion

Tumoral vascularization

Study of intra-renal arteriesMorpho-hemodynamic study


Arterio-venous fistula Pseudo-aneurysm

Intermediate PRF

Renal stones Vascular calcifications

High PRF

Normal kidneyPower Doppler

Increases sensitivity to low flow

Less angle-dependent

Good visualization of the entire renal vascular tree

Zubarev AV. Eur Radiol 2001 ; 11 : 1902 – 1915.

Normal pulse Doppler waveformRenal segmental artery

Sharp systolic upstroke

Low resistance waveform

Continuous forward diastolic flow

Pourcelot’s resistive index

RI S – ED / S

Normal 50 – 70 %

Abnormal > 80 %

Accleration time (AT)or Rise time (RT)

• Length of time in sec from

onset of systole to peak systole

• Normal value: < 0.07 second

Acceleration Index (AI)

AI = X (KHz)

Probe frequency (MHz)

Normal value: > 3.5 m/s2

Systolic upslope/transducer frequency

Measurement of PSV

Early systolic peak

Am J Roentgenol – Dec 1995

Biphasic with late systolic peak

Monophasic with late systolic peak

Early systolic notch


Some normal waveforms have early systolic notch

1. Measuring to point of PSV results in prolonged AT & AI

2. Excellent negative predictive value of stenosis > 60%

Extrasystole


Correct RI calculated in normal sinusoidal rhythm

Spectral Doppler of renal arteriesNormal values

• PSV < 180 cm/sec

• Renal Aortic Ratio (RAR) < 3

• Resistive index (RI) < 0.70

• ∆ RI (right – left) < 0.05

• Acceleration Time (AT) < 0.07 sec

• Acceleration Index (AI) > 3.5 m/s2

Doppler ultrasound of the kidneys 1

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