Doppler ultrasound of the kidneys 1

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Selection of Patients for Renal Doppler. and Technique

Selection of Patients for Renal Doppler. and Technique

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  • The normal adult kidney is bean shaped with a smooth convex contour anteriorly, posteriorly, andlaterally. Medially, the surface is concave and known as the renal hilum. The renal hilum is continuous with a central cavity called the renal sinus. The collecting system (renal pelvis) lies posterior to the renal vessels in the renal hilum.
  • ● The right renal artery is longer than the left, and passes posterior to the IVC.● The left renal artery has a more horizontal course to the kidney.
  • Anomalous left-sided IVC from persistence of the embryological azygos vein.
  • Discrepancy of more than 2 cm between the lengths of two kidneys is considered significant and needs further evaluation.The renal parenchyma is composed of cortex and medullary pyramids.The renal medullary pyramids are hypoechoic relative to the renal cortex and can be identified in most normal adults.The normal renal cortex has classically been described as being less echogenic than adjacent liver and spleen. Platt et al. evaluated 153 patients and found that 72% of patients with renal cortical echogenicity equal to that of the liver had normal renal function.If renal echogenicity greater than the liver were used as the criterion, both specificity and positive predictive value for abnormal renal function rose to 96% and 67%, respectively. However, sensitivity is poor-only 20%.
  • Easily differentiated from renal mass:1- similar echotexture to adjacent renal parenchyma on gray-scale ultrasound.2- CFD and PD will demonstrate similar perfusion to that of adjacent renal parenchyma.
  • Another common renal variant that can be mistaken for renal scarring, a consequence of chronic infective process of the kidneys. Persistent fetal lobulation can be differentiated from scarred kidneys by the location of the renal surface indentations, which do not overlie the medullary pyramids as in true renal scarring, but overlie the space between the pyramids.The underlying medulla and the cortex are normal
  • Prominent cortical tissue that is present between the pyramids and projects into the renal sinus. Prominent columns of Bertin are usually seen in the middle third of the kidney and are more common on the left side.
  • During normal development, there is partial fusion of two parenchymal masses called renunculi. Parenchymal junctional defects occur at site of fusion & must not be confused with pathologic processes such as renal scars & angiomyolipoma. Junctional parenchymal defect is most typically located anteriorly and superiorly and can be traced medially & inferiorly into renal sinus. Usually, it is oriented more horizontally than vertically; therefore, it is best appreciated on sagittal scans.It is seen more often on the right; however, when a good acoustic window is present (splenomegaly), it can also be seen on the left.
  • Normally, the glands are 0.3 to 0.6 cm in thickness, 4 to 6 cm in length, and 2 to 3 cm in width.
  • The traditional view resulting from studies in the 1970’s and 1980’s that successful ultrasound imaging of the adrenal glands is the exception has been invalidated by the development of modern ultrasound diagnostics and should no longer affect the application of US.
  • One of the most complex and difficult sonographic examination.
  • Accessory renal arteries from the aorta to the upper or lower poles of the kidney in 15 -24 %.In a study performed by Bude and colleagues, a hemodynamically significant stenosis isolated to an accessory renal artery was found inonly 1.5% of patients undergoing angiography for evaluation of RVH. This study concluded that failure to evaluate accessory renal arteries should not negatively affect the usefulness of a noninvasive study for detecting RVH.
  • Even expert sonographers detect only 80–90 per cent of renal arteries.Ultrasound contrast agents improve the technical success rate to 95 per cent.

Transcript

  • 1. Doppler ultrasound of the kidneys Dr. Muhammad Bin Zulfiqar PGR FCPS SHL
  • 2. 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
  • 3. 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
  • 4. 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)
  • 5. Arterial blood supply to the Kidney Myers KA & Clough A. Making sense of vascular ultrasound. Arnold, London, 2004. Segmental artery Apical, upper, middle, lower, posterior Interlobular artery Between renal pyramids Glomerular arteriole Main renal artery Arcuate artery Between cortex & medulla
  • 6. Left renal vein • Longer than right renal vein • Averages 85 mm in length (range: 60 – 110 mm) • Joined by adrenal, gonadal, lumbar, & hemiazygous veins 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.
  • 7. Variants of left renal vein Retro-aortic LRV Incidence: 2 – 3% Circum-aortic LRV Incidence: 7 – 9% Sidhu R et al. Semin Ultrasound CT MRI 2009 ; 30 : 271 – 288.
  • 8. 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
  • 9. 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
  • 10. Gray scale imaging first • Kidneys Maximum renal length Echogenicity of renal cortex Thickness of renal cortex Masses – hydronephrosis – renal calculi • Aorta Plaque – thrombus – dissection – aneurysm • Adrenal glands
  • 11. Normal kidney Longitudinal 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)
  • 12. 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.
  • 13. 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.
  • 14. 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. Fiorini F et al. J Ultrasound 2007 ; 10 : 161 – 167. Adjusted to BMI (V / BMI) . 25 Appropriate renal volume 231 50 ml
  • 15. 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
  • 16. Kidney parenchyma compared to liver parenchyma Hypoechoic Isoechoic Hyperechoic Fiorini F et al. J Ultrasound 2007 ; 10 : 161 – 167.
  • 17. Congenital normal variants of kidney • Dromedary hump • Persistent fetal lobulation • Prominent column of Bertin • Junctional parenchymal defect • Hypoechoic renal sinus Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41.
  • 18. Dromedary hump Common renal variation Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41. Focal bulge on lateral border of left kidney Result from adaptation of renal surface to adjacent spleen Easily differentiated from renal mass by Doppler
  • 19. Persistent fetal lobulation Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41. Renal surface indentations between pyramids May be single or multiple
  • 20. Prominent column of Bertin (PCB) Mistaken for intrarenal tumor Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41. Continuity with renal cortex Similar echo pattern as renal parenchyma Similar vascular pattern by color & power Doppler
  • 21. Junctional fusion defect Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41. 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
  • 22. 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.
  • 23. 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.
  • 24. US of normal adrenal glands Documented 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 training US can image right gland in 99% & left gland in 70%1 Transcostal scan in LLD Between RLL, IVC & diaphragm Right adrenal gland Left adrenal gland Transverse scan of epigastrium Dorsal to pancreatic tail & SV
  • 25. 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.
  • 26. 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
  • 27. 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
  • 28. 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
  • 29. Transverse scan with probe angulations Main renal arteries Schäberle W. Ultrasonography in vascular diagnosis. Springer-Verlag, Berlin, 2nd edition, 2011.
  • 30. 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
  • 31. Gray scale alone without color Doppler Patients with difficulty to hold breath Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475. Entire RRA well visualized Color flash artifact from patient motion may obscure visualization Better spatial resolution & and faster frame rate Gray scale image
  • 32. Norma left renal artery Gray scale image Color Doppler image Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475. Proximal main left renal artery Proximal main left renal artery
  • 33. ‘‘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
  • 34. Normal right renal artery Coronal images of IVC Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475. RRA is the only vessel to course laterally under the IVC Often slightly indents the IVC
  • 35. 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
  • 36. Longitudinal scan in left lateral decubitus Multiple renal arteries (25%) Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475.
  • 37. Two left renal arteries Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. PSV: 90 cm/sec Dominant left renal artery PSV: 60 cm/sec Accessory left renal artery
  • 38. Axial scan in left lateral decubitus Using right kidney as acoustic window Right main renal artery & vein Color Doppler USSchematic drawing Meola M et al. J Ultrasound 2008 ; 11 : 55 – 73.
  • 39. Axial scan in right lateral decubitus Using left kidney as acoustic window Schematic drawing Left main renal artery & vein Color Doppler US Zubarev AV. Eur Radiol 2001 ; 11 : 1902 – 1915.
  • 40. Pre caval right renal artery
  • 41. Pre-aortic left renal vein (80 – 95%) Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. Reduction in diameter in pre-aortic segment to IVC with physiologic acceleration
  • 42. Left renal vein variants Sidhu R et al. Semin Ultrasound CT MRI 2009 ; 30 : 271 – 288. Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. Retro-aortic LRV (2 – 3%) Circum-aortic LRV (7 – 9%) Pre & retro-aortic LRV
  • 43. Color Doppler of RRV & retro-hepatic IVC Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. Righ renal vein Inferior vena cava
  • 44. Pulsed Doppler of renal veins Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. Right renal vein Resembles pulsed Doppler of IVC Triphasic waveform Left renal vein Little modulation Wall artifact due to systolic peak
  • 45. 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) Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475. Expert sonographers detect 80 – 90% of main RA CEUS improves success rate to 95%
  • 46. Angle of insonation Difficulty in case of tortuous or curved renal artery Correct angleIncorrect angle Schäberle W. Ultrasonography in vascular diagnosis. Springer-Verlag, Berlin Heidelberg, 2nd edition, 2011.
  • 47. Adjustment of Doppler control Low flow settings • Lowest pulse repetition frequency without aliasing • Small color box • Greatest gain without background noise • Lowest wall filter • High color priority
  • 48. 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)
  • 49. Study of intra-renal arteries Perfusion study / Low PRF Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. Cortical perfusion Tumoral vascularization
  • 50. Study of intra-renal arteries Morpho-hemodynamic study Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. Arterio-venous fistula Pseudo-aneurysm Intermediate PRF Renal stones Vascular calcifications High PRF
  • 51. Normal kidney Power 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.
  • 52. Normal pulse Doppler waveform Renal segmental artery Sharp systolic upstroke Low resistance waveform Continuous forward diastolic flow
  • 53. Pourcelot’s resistive index RI S – ED / S Normal 50 – 70 % Abnormal > 80 %
  • 54. Accleration time (AT) or Rise time (RT) • Length of time in sec from onset of systole to peak systole • Normal value: < 0.07 second
  • 55. Acceleration Index (AI) AI = X (KHz) Probe frequency (MHz) Normal value: > 3.5 m/s2 Systolic upslope/transducer frequency
  • 56. Measurement of PSV Early systolic peak Am J Roentgenol – Dec 1995 Biphasic with late systolic peak Monophasic with late systolic peak
  • 57. Early systolic notch Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475. 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%
  • 58. Extrasystole Hélénon O et al. EMC-Radiologie 2005 ; 2 : 367 – 412. Correct RI calculated in normal sinusoidal rhythm
  • 59. Spectral Doppler of renal arteries Normal 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