Doppler ultrasound of the kidneys

Normal anatomy of the kidney

• :

Renal parenchymacortex

Renal sinus:arteries,veins, lymphatic, collecting systemRenal hilum: Concave, renal sinus

Anatomy of renal arteries

• RRA: Usually passes posterior to inferior vena cava

• LRA: Usually courses posterior to left renal vein

Arterial blood supply to the Kidney

Segmental artery

Apical, upper, middle, lower, posterior

Interlobular artery

Between renal pyramids

Glomerular arteriole

Main renal artery

Arcuate artery

Between cortex & medulla

Left-sided IVCNormal anatomy of

IVC

Anomalous left-sided IVC

Indications of Renal Doppler Ultrasound

1-Renal Artery Stenosis2-Renal Artery Thrombosis 3-Renal Artery Emboli4-Renal vein thrombosis5-Aneurysm & Pseudo Aneurysm6-Arterio-venous communications7-Renal mass8-Hypertension in Young age

Gray scale imaging firstKidneys

renal length Echogenicity of renal cortexThickness of renal cortexMasses hydronephrosis renal calculi

AortaPlaque – thrombus – dissection – aneurysm

Normal kidneyLongitudinal section Cross section

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Renal capsule: echogenic lineRenal parenchyma: outer cortex & inner medulla

pyramidCentral sinus complex: high echogenicity

(vessels, fat, fibrous tissue)

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

Appropriate renal volume231 ± 50 ml

Cortical thickness: 8 – 10 mm

Parenchymal thickness: 14 – 18 mm

Classification of renal parenchymal echogenicity

4 types based of US appearanceHypoechoic compared to liver

Isoechoic compared to liver

Hyperechoic compared to liver

Isoechoic to renal sinus

Normal

Normal

Pathological

Pathological

Grade 0Grade IGrade IIGrade III

Kidney parenchyma compared to liver parenchyma

Hypoechoic Isoechoic

Hyperechoic

Congenital Normal Variant

• Dromedary Hump

• Fetal Lobulation

• Prominent column of bertin

• Junctional Parenchymal defect

• Hypoechoic renal sinus

Dromedary hump Fetal lobulation

Common 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

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

Normal right renal artery

Transverse gray scale image

Right main renal artery

Transverse color Doppler image

Right main renal artery

Normal left renal arteryGray scale image Color Doppler image

Proximal main left renal artery Proximal main left renal artery

Axial scan in left lateral decubitusUsing right kidney as acoustic window

Right main renal artery & vein

Color Doppler USSchematic drawing

Axial scan in right lateral decubitusUsing left kidney as acoustic window

Schematic drawing

Left main renal artery & vein

Color Doppler US

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

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 RA

CEUS improves success rate to 95%

Angle of insonationDifficulty in case of tortuous or curved renal artery

Correct angle Incorrect angle

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

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

Normal inter-lobar renal arteries (short arrows)

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

Early systolic notch

Some normal waveforms have early systolic notch

Measuring to point of PSV results in prolonged AT & AIExcellent 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

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