Diana Pancu, MD

RENAL ULTRASOUND

Objectives

• 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

IVC

AO

RT

A

Celiacaxis

SMA

Renal artery

Renal vein

HepaticVeins

Rightkidney

Left kidney

Liver

Spleen

Renal Scanning Approaches

Approach to Scanning

• 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

I

LIVER STOMACH

SP

LE

EN

IVC

AORTAK K

S

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

Renal artery

Renal vein

Ureter

Renal capsule Cortex

Medullary pyramids

Minor Calyx

Kidney Anatomy

Medulla

Sinus

Major Calyx

Sonographic Appearance

• 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

Liver

Diaphragm

Sinus

Cortex

Anterior

Posterior

Superior Inferior

Right Kidney Long Axis

Right Kidney Short Axis

Right Kidney Short Axis

VertebralBody

R KidneyAortaRenal a.

GB

IVC

Liver

Anterior

Posterior

Right Left

Left Kidney Long Axis

Left Kidney Long Axis

Anterior

Posterior

Superior Inferior

Spleen

Kidney

Rib Shadow

Left Kidney Short Axis

Left Kidney Short Axis

Anterior

Posterior

Right LeftLiver

Spleen

L Kidney

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

– Sinclair D, Wilson S, Toi A, et al. Ann Emerg Med 18:556-559, 1989  

ULTRASOUND Sensitivity=85%Specificity=92%

IVPSensitivity=90%Specificity=94%

Radiographic Modalities

ED Ultrasound + KUB vs. IVP• Prospective study, 108 patients

Sensitivity = 97%Specificity = 59%

Henderson, S, et al: Acad Emerg Med.1998;5:666-671.

Sensitivity = 97%Specificity = 59%

PPV = 81% NPV = 92%

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 CTSecondary Findings

Sensitivity• Ureteral dilatation 90%• Perinephric stranding 82%• Collecting system

dilatation 83%• Renal enlargement 71%

Specificity• 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

– 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– Renal lithiasis– Neoplasm (renal, ureteral, bladder)– Papillary necrosis – Ureterocele– Blood clot– Neurogenic bladder– Anticholinergics– Pregnancy, PID, uterine prolapse)– Diuretics– Vesico-ureteral reflux– Diabetes insipidus

• Intrinsic, congenital– Stenosis (ureteral,

urethral, meatal)

– Adynamic ureter

– Spinal cord defects

– Duplication of the ureter

– Ureterocele

Hydronephrosis in Renal Colic

Smith. AJR Am J Roentgenol. 1996; 167:1109-1113

Sensitivity = 90%Specificity = 93%

PPV = 92%NPV = 90%

Dalrymple. J Urol. 1997; 159:735-740  

Sensitivity = 87%Specificity = 90%

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

Kidney Liver

GB

Moderate - Severe Hydronephrosis

LiverKidneyDilated pelvis

GB

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

Kidney

Cyst

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

Liver

Diaphragm

Kidney

Mass

RibShadow

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

2. Renal Masses

Renal Pathology

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

Thin ParenchymaDilated Calyces

Distinct Shadow

Echogenic Structure

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