Renal Ultrasound

RENAL ULTRASOUND

Diana Pancu, MD

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

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 • • • • •

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 – – – – – – –

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 – – – – – – – – – – –

• 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