Beyond Hydronephrosis: Ultrasound of the Kidneys with CT ...

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Beyond Hydronephrosis: Ultrasound of the Kidneys with CT and MR correlation

Brian C. Allen, MDMelanie P. Caserta, MD

Downloaded from sar2013.conferencespot.org

LEARNING OBJECTIVES

Indications for US InfectionRenal MassesEchogenic structuresVascular


INDICATIONS FOR RENAL ULTRASOUND

Renal Failure – evaluate for hydronephrosis (rare cause), medical renal disease Hematuria – stones, mass Complications of Infection Congenital vs acquired anomalies Characterize lesions seen by CT – is it a cyst or solid

mass? Renal Vascular Evaluation Renal vein thrombosis Renal artery stenosis (MRA or CTA study of

choice) AVF, pseudoaneurysm etc…


RENAL INFECTION: IMAGING APPROACH

Uncomplicated pyelonephritis No imaging needed Often normal imaging appearance

Complicated pyelonephritis US – primary role to look for complications Evaluate for pyonephrosis, large renal/perirenal

abscesses, obstruction, stones as possible nidus for infection

CT Small abscesses, gas forming infection


PYELONEPHRITIS

Focal pyelonephritis may appear echogenic due to hemorrhage

Look For:Renal enlargementHypo or hyper echogenicityPatchy echogenicityThickened urotheliumLoss of CM differentiationAbscess


COMPLICATIONS OF PYELONEPHRITIS: ABSCESS

Look for: Poorly marginated, thick

walled hypoechoic mass Internal debris Acoustic enhancement May appear solid

Should not have internal flow

Stones or gas Perinephric extension

Standard treatment Percutaneous drainage +

antibiotics If small, can be treated

effectively with antibioticsDownloaded from sar2013.conferencespot.org

COMPLICATIONS OF RENAL INFECTION: PYONEPHROSIS

Look for: Presence of mobile debris and

layering material in a hydronephrotic kidney This is an accurate (96%) sign to

differentiate pyonephrosis from hydronephrosis in patients with clinical evidence of renal infection1

Thickening of urothelial lining Treatment = percutaneous

nephrostomy Can cause rapid and permanent

decrease in renal function Can progress to sepsis if not

treated quickly

1 AJR 1983;140: 991-993.Downloaded from sar2013.conferencespot.org

COMPLICATIONS OF RENAL INFECTION: EMPHYSEMATOUS PYELONEPHRITIS

Almost exclusively in diabetics Also seen in immunocompromised Obstruction is also a risk factor

Aggressive variant of acute pyelonephritis Can be fatal

Two types Type I = True emphysematous pyelonephritis Surgical emergency – Tx is nephrectomy + Abx

Type II = Renal or perirenal fluid and gas containing abscess +/- gas in renal pelvis

If suspected on US Get a CT to determine location and extent of gas


COMPLICATIONS OF RENAL INFECTION: EMPHYSEMATOUS PYELONEPHRITIS

Highly echogenic areas within renal parenchyma with shadowing Ring down artifacts from air bubbles Gas in perinephric space may obscure kidney

COURTESY OF HISHAM TCHELEPI, MDDownloaded from sar2013.conferencespot.org

RENAL INFECTION: LESS COMMON ENTITIES

Tuberculosis Infection = reactivation of hematogenous spread Most common clinical manifestation of extrapulmonary TB1

General Imaging Features in Urinary Tract Calcification Cavities Strictures +/- Abdominal LAD

Xanthogranulomatous pyelonephritis (XGP)2

Chronic inflammatory process associated with longstanding obstruction Pathologic response to infection is the formation of inflammatory masses by lipid

laden macrophages Organisms: P. mirabilis, E. coli

Opportunistic Infection (Immunocompromised patients) Transplant patients at risk Fungal Infection

HIV nephropathy1 RadioGraphics 2007; 27:1255-1273 2 RadioGraphics 2008; 28: 255-276 Downloaded from sar2013.conferencespot.org

RENAL INFECTION: LESS COMMON ENTITIES

TB US insensitive for early disease but look for1: Irregular hypoechoic masses connecting to collecting system

without hydronephrosis Papillary destruction/necrosis Echogenic masses in pyramids Distorted renal contour Calcifications Urothelial mucosal thickening Small fibrotic thick walled bladder

XGP US appearance Staghorn stone in pelvis + dilated calyces Perinephric fluid Perinephric inflammatory tissue Anechoic or hypoechoic round masses replacing renal parenchyma

1 RadioGraphics 2007; 27:1255-1273Downloaded from sar2013.conferencespot.org

BILATERAL ENLARGED KIDNEYS: DDX

Medical HIV Acute glomerulonephritis Amyloidosis Multiple myeloma Diabetes

Inflammatory Acute tubular necrosis Acute interstitial nephritis

NeoplasmLeukemia/LymphomaMets

VascularRenal vein thrombosisVasculitides

Bilateral Enlarged Echogenic Kidneys in HIV Nephropathy


RENAL MASS:IMAGING APPROACH

Cyst or solid? Internal architecture of a cystic lesion is often better seen on US

than on CT Expansile vs Infiltrative (Ball vs Bean)? Fat containing? Solitary or Multiple? Low threshold for recommending CT or MR if suspect a mass Watch out for mimics of mass – high frequency techniques may help

sort these out Dromedary hump Fetal Lobulation Focal parenchymal hypertrophy adjacent to scar

TCC Faceless kidney appearance Fungus ball and blood clot in ddx when see material in collecting

system


CYST

US can show more complex internal architecture than CT Don’t apply the Bosniak Classification to cysts on US1

Simple Cyst Complex cyst Recommend CT/MRI for further

characterization if: Thickened wall Multiple or thick septations Extensive mural or septal calcification Mural or septal nodularity Thick or nodular calcifications

6 month follow up US if: Internal echoes Few thin septations

1 Radiology 2011; 262: 781-785Downloaded from sar2013.conferencespot.org

ANGIOMYOLIPOMA

Most common benign renal tumorMost are detected incidentally Tumor size >4cm = increased bleeding risk Lipid rich AML is characteristically echogenic

BUT need to confirm fat content!May have increased flow on color Doppler

which can make it difficult to differentiate from RCCApprox 1/3 of small (<3cm) hyperechoic

masses at US may represent RCC1

1 Radiology. 1993; 188:431-434.Downloaded from sar2013.conferencespot.org

ECHOGENIC RENAL FOCI

Nephrolithiasis Vascular calcificationsNephrocalcinosisGas forming infectionPapillary necrosisCystic disease


NEPHROLITHIASIS

Gray-scale – sensitivity of 24-57% compared to CT1,2

Stones of sufficient size – echogenic and shadow Small stones (< 5 mm) – echogenic

Color Doppler – color comet-tail or “twinkle” artifact May increase sensitivity, but overestimates size Positive predictive value = 78-94%3,4

False negatives: Smooth surfaced stones (uric acid and calcium oxalate monohydrate stones) may not twinkle5

False positive – vascular calcification and refractive shadowing from renal sinus fat, non-calcified foci

1 Radiology 2002;222:109-13 2 J Clin Ultrasound 2007;235:256-613 Radiology 2011;259:911-6 4 J Ultrasound Med 2012;31:1619-1625 5 AJR 2003;180:215-22Downloaded from sar2013.conferencespot.org

MEDULLARY NEPHROCALCINOSIS

Calcification of the renal pyramids rather than the collecting systemDDx – medullary sponge kidney, renal

tubular acidosis and hyperparathyroidismGray-scale Early – echogenicity at tip or periphery of

medullary pyramids (Anderson-Carr kidney)Progresses to diffusely increased

echogenicity and shadowingSonographic findings (crystallization) predate

radiograph and CT findingsDownloaded from sar2013.conferencespot.org

CORTICAL NEPHROCALCINOSIS

Calcification of the renal cortexDDx – renal cortical necrosis, oxalosis,

Alport’s syndrome, transplant rejection, chronic glomerulonephritisGray-scaleEchogenic renal cortexLoss of corticomedullary differentiationPosterior acoustic shadowing


PAPILLARY NECROSIS

Renal medulla and papillae are vulnerable to ischemic necrosis due to blood supply and hypertonic environment

Causes: Diabetes, analgesic abuse, sickle cell disease, obstructive uropathy, pyelonephritis, renal vein thrombosis, tuberculosis

Gray scale Hypoechoic papillae Cystic spaces in the medullary pyramids; may mimic

caliectasis Echogenic foci in the medullary pyramid represents

necrotic papillae Hydronephrosis is common

Color Doppler Sloughed papillae may cause a color comet-tail artifact May mimic renal calculi


GAS

Emphysematous pyelonephritis – rare, life threatening necrotizing infectionEmphysematous pyelitis – gas within the

collecting system, more benign clinical courseGray-scaleEchogenic fociReverberation artifact (“dirty” shadowing)

in non-dependent positionRequires high index of suspicion


LITHIUM TOXICITY

Chronic lithium use may lead to nephrogenic diabetes insipidus and chronic renal insufficiency Tubulointerstitial nephritis, with tubular microcysts

and interstitial fibrosis DDx includes polycystic renal disease and

glomerulocystic disease Ultrasound 1-2 mm microcysts may appear as echogenic foci

and may be misinterpreted as calcifications High frequency transducers, harmonic imaging,

cine clips allow identification of enhanced through transmission *

* J Ultrasound Med 2012; 31: 637-44Downloaded from sar2013.conferencespot.org

VASCULAR LESIONS

Arteriovenous fistulaPseudoaneursymNutcracker syndromeRenal arterial hypertensionRenal vein thrombosis


PSEUDOANEURYSM

Etiology Penetrating trauma – stab and gunshot wounds Iatrogenic - percutaneous biopsy, nephrostomy

tube placement, surgery Tumors Vasculitis

Symptoms: Gross hematuria, flank pain, hypertension Treatment None – many heal spontaneously* Coil embolization

*Clin Nephrol 2002;58:398-404Downloaded from sar2013.conferencespot.org

PSEUDOANEURYSM

Gray scale – cystic spacesDuplex color DopplerSwirling pattern in the lumen (“yin-yang”) “to and fro” flow in the neck – flow in

during systole and out during diastolePseudoaneurysms are often associated with

arteriovenous fistulas *Low resistance high velocity pattern

* Ultrasound The Requisites, 2nd Ed, p.143Downloaded from sar2013.conferencespot.org

ARTERIOVENOUS FISTULA

Etiology Penetrating trauma – stab and gunshot wounds Iatrogenic Percutaneous biopsy Nephrostomy tube placement Surgery

May be asymptomatic, gross hematuria, urinary tract obstruction, renal insufficiency or hypertension Treatment None – 75% spontaneously close at 4 weeks* Coil embolization

*Clin Nephrol 2002;58:398-404Downloaded from sar2013.conferencespot.org

ARTERIOVENOUS FISTULA

Often no changes on gray scale unless accompanied by a pseudoaneurysmDuplex color Doppler Increased arterial peak systolic and

diastolic velocityDecreased resistanceArterialization of the draining veinSoft tissue vibration


NUTCRACKER SYNDROME

Renal vein entrapment syndrome Compression of the left renal vein between the aorta

and SMA Elevated renal vein pressure Collateral vessels

Young, previously healthy patients Intermittent gross hematuria, +/- flank pain Ultrasound: Compression of the renal vein Elevated flow velocity using Duplex color Doppler *

3 mm Hg gradient at angiography is used to diagnose renal venous hypertension

• Radiology 1996; 198: 93-7• AJR 1999; 172: 39-43


Beyond Hydronephrosis: Ultrasound of the Kidneys with CT ...

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