RENAL ULTRASOUND
Diana Pancu, MD
Objectives
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Clinical indications for performing ED renal US
Approach to performing the US study
Normal anatomy
Abnormal findings
Clinical Impact
Clinical Indications for ED
Renal Ultrasound
• Suspected renal colic
– Colicky flank pain radiating to groin
– Hematuria
• Clinical question:
– Presence of hydronephrosis
– Absence of other pathology (AAA)
Performing the Study
• Patient preparation:
– none
• Transducer: 3.0MHz or 3.5 MHz
– 5.0 MHz for thin patient
• Patient positioning
– Supine
– Posterior oblique, lateral decubitus, prone
Anatomy
• Kidneys are retroperitoneal, T12 - L4
• Right kidney is lower than the left kidney
• Right kidney is posterio-inferior to liver &
gallbladder
• Left kidney is inferior-medial to the spleen
• Adrenal glands are superior, anterior,
medial to each kidney
Hepatic
Veins
Spleen
Celiac
axis
Liver
SMA
Right
kidney
Renal artery
Renal vein
Left
kidney
Renal Scanning Approaches
Approach to Scanning
LIVER
STOMACH
I
K
AORTA
K
IVC
S
• Right kidney scanning
approach: anterior,
lateral, posterior
• Liver is the acoustic
window
• Left kidney: requires a posterior
approach, through the spleen
• Air-filled bowel impedes
anterior scanning
Anatomy
• 9-12 cm long, 4-5 cm wide, 3-4 cm thick
• Gerota’s fascia encloses kidney, capsule,
perinephric fat
• Sinus
– Hilum: vessels, nerves, lymphatics, ureter
– Pelvis: major and minor calyces
• Parenchyma surrounds the sinus
– Cortex: site of urine formation, contains nephrons
– Medulla: contains pyramids that pass urine to minor
calyces. Columns of Bertin separate pyramids
Medullary pyramids
Kidney Anatomy
Minor
Calyx
Major
Calyx
Sinus
Medulla
Renal capsule
Cortex
Sonographic Appearance
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Ureters are normally not seen
Renal pelvis is black when visible
Renal sinus is echogenic due to fat
Medullary pyramids are hypoechoic
Cortex is mid-gray, less echogenic than
liver or spleen.
• Capsule is smooth and echogenic
Right Kidney Long Axis
Right Kidney Long Axis
Anterior
Superior
Liver
Inferior
Sinus
Cortex
Diaphragm
Posterior
Right Kidney Short Axis
Right Kidney Short Axis
Anterior
Right
GB Liver
Left
IVC
R Kidney
Vertebral
Body
Posterior
Aorta
Renal a.
Left Kidney Long Axis
Left Kidney Long Axis
Anterior
Superior
Inferior
Rib
Shadow
Kidney
Posterior
Spleen
Left Kidney Short Axis
Left Kidney Short Axis
Anterior
Right Liver
Left
Spleen
L Kidney
Posterior
Common Pitfalls in
Renal Scanning
• Failure to scan both kidneys
• Mistaking prominent renal pyramids for
hydronephrosis
• Mistaking prominent pyramids for cysts
• Confusing normal renal arteries for the
ureter
Common Pitfalls in
Renal Scanning
• Failure to scan through the bladder to search
for stone at the uretero-vesicular junction
• Inability to visualize left kidney due to
anterior probe placement
• Failure to scan the aorta in suspected renal
colic
Normal Variants
• Dromedary humps:
– Lateral kidney bulge, same echogenicity as the cortex
• Hypertrophied column of Bertin:
– Cortical tissue indents the renal sinus
• Double collecting system:
– Sinus divided by a hypertrophied column of Bertin
• Horseshoe kidney:
– Kidneys are connected, usually at the lower pole
• Renal ectopia:
– One or both kidneys outside the normal renal fossa
Clinical Indications
1. Obstructive Uropathy
Nephrolithiasis
• 12% of the US population
• Incidence of renal colic is 3% with
50% recurrence within 10 years
– Manthey DE. Emerg Med Clin North Am.2001;
19(3): 633-54
Radiographic Modalities
Radiography
• 62% Sensitivity, 67% Specificity
– Sharma RN, Shah I, Gupta S, et al:
Thermogravimetric analysis of urinary stones.
Br J Urol 64:564-566, 1989
Radiographic Modalities
IVP vs. US
• Prospective study, 85 patients
ULTRASOUND
Sensitivity=85%
Specificity=92%
IVP
Sensitivity=90%
Specificity=94%
– Sinclair D, Wilson S, Toi A, et al. Ann Emerg
Med 18:556-559, 1989
Radiographic Modalities
ED Ultrasound + KUB vs. IVP
• Prospective study, 108 patients
Sensitivity = 97%
Specificity = 59%
Sensitivity = 97%
Specificity = 59%
PPV = 81%
NPV = 92%
Henderson, S, et al: Acad Emerg Med.1998;5:666-671.
Radiographic Modalities
Helical CT- Gold Standard
• Accurate, fast, no contrast
• Identifies presence and size of stone
• Location of stone
• Level of obstruction
• Other sources of pain
Stone on CT
• Usually visualized
• Not visualized
– Stone is extremely small < 1 mm
– Stone is of relatively low CT attenuation:
Indinavir stones
– Stone excluded from imaging due to respiratory
variation
Helical CT
Secondary Findings
Sensitivity
Specificity
• Ureteral dilatation 90%
• Perinephric stranding 82%
• Collecting system
dilatation 83%
• Renal enlargement 71%
• Ureral dilatation 93%
• Perinephric stranding 93%
• Collecting system
dilatation 94%
• Renal enlargement 89%
Smith. AJR Am J Roentgenol 167:1109-1113, 1996
Location of Stone
• 378 patients
• Rate of spontaneous stone passage
• 22% for proximal ureteral stones
• 46% for midureteral stones
• 71% for distal ureteral stones
– Morse R. J Urol. 1991; 145:263-265
Width of Stone
• 520 patients
• Rate of spontaneous stone passage
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100% for stones that were 1 mm or smaller in width
90% for stones 2 to 3 mm
80% for stones that were 4 mm
55% for stones that were 5 mm
35% for stones that were 6 mm
25% for stones that were 7 mm
12% for stones that were 8 mm
• Ueno A. Urology. 1977; 10:544-546
Radiographic Modalities
Ultrasound
• Fast
• Can identify other causes of pain
• Safe in pregnant patients, children
Hydronephrosis
Dilatation of the urinary tract at any level
secondary to intrinsic and or extrinsic
obstruction to urine flow
Hydronephrosis
• Intrinsic, acquired
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• Intrinsic, congenital
Renal lithiasis
Neoplasm (renal, ureteral, bladder)
Papillary necrosis
Ureterocele
Blood clot
Neurogenic bladder
Anticholinergics
Pregnancy, PID, uterine prolapse)
Diuretics
Vesico-ureteral reflux
Diabetes insipidus
– Stenosis (ureteral,
urethral, meatal)
– Adynamic ureter
– Spinal cord defects
– Duplication of the
ureter
– Ureterocele
Hydronephrosis in Renal Colic
Sensitivity = 90%
Specificity = 93%
PPV = 92%
NPV = 90%
Smith. AJR Am J Roentgenol. 1996; 167:1109-1113
Sensitivity = 87%
Specificity = 90%
Dalrymple. J Urol. 1997; 159:735-740
PPV = 90%
NPV = 89%
Obstructive Uropathy
Grading System - Subjective
• Mild
– Minimal separation of calyces
• Moderate
– Dilation of major and minor calyceal system
• Severe
– Marked dilation of the renal pelvis and thinning
of the renal parenchyma
Range of Hydronephrosis
Normal
Mild
Moderate
Severe
Mild Hydronephrosis
GB
Kidney
Liver
Moderate - Severe
Hydronephrosis
GB
Liver
Kidney
Dilated pelvis
Renal Pathology
1. Renal Cysts
Renal Cysts
• Arise in the renal cortex, commonly single rather
than multiple
• Cysts do not communicate; hydronephrosis does
• Shape is round or oval
• Echo free
• Sharp interface between the mass and renal tissue
• Large renal cysts may be mistaken for aortic
aneurysms
Renal Cysts
Liver
Cyst
Kidney
Scatter 20
Bowel
Problems & Pitfalls
• Mistaking cysts for hydronephrosis
• Mistaking cysts for aortic aneurysm
Case Presentation
• 40 yo male presents with complaints of
recent severe headaches, diaphoresis,
and palpitations
• PE anxious male
– BP 210/120 HR 145 RR 18 T 99
– Physical exam otherwise normal
Ultrasound of Kidneys
Kidney
Liver
Diaphragm
Rib
Shadow
Mass
Case Development
• The patient was managed with alpha and
beta-adrenergic blocking agents
• Urine studies revealed elevated
metanepherine and catecholamine levels
• The patient was diagnosed with
pheochromocytoma
Renal Pathology
2. Renal Masses
Renal Masses
• Ultrasound visualizes most solid and cystic renal masses
• Beyond scope of EM ultrasound
• Appearance
– Irregular borders
– Poorly defined interfaces between mass and kidney
• Complex masses
– Complex ultrasonic appearance
– Cysts or solid masses may represent infection or hemorrhage
– May have fluid levels
Case Presentation
• 35 year old male with history of Crohn’s presents
with sudden onset of right flank pain. He is
nauseated and has vomited a few times. He
reports hematuria and denies fever, dysuria,
abdominal pain.
Physical Exam
Young man in moderate distress from pain
• BP 125/67
HR 110 T 98
• Lungs: clear to ascultation
• Heart: Tachycardia without murmur
• Abdomen: soft, non-tender, normal bowel
sounds
• Back: right costo-vertebral angle tenderness
on percussion
Renal Ultrasound
Right Kidney
Left Kidney
Ultrasound
Echogenic
Structure
Distinct Shadow
Thin Parenchyma
Dilated Calyces
CT Results
• Bilateral Staghorn Calculi
• Bilateral moderate hydronephrosis
• Right sided 3 mm stone at the UVJ
Summary & Take-Home Points
• US is an adjunct in the evaluation of
patients with suspected renal colic
– Evaluate kidneys
– Evaluate aorta
• Scan both kidneys