Radiologists’ role in nephrolithiasis

RADIOLOGISTS’ ROLE IN

NEPHROLITHIASIS

May 2012Dr W.J. Conradie

Department of Diagnostic Radiology

CON

TENTS

Click icon to add picture•Nephrolithiasis• Definition• Incidence• Classification

• Factors influencing treatment decision

• Imaging approach• Adults• Children• Pregnancy

•Role in management • Antegrade pyelography• Percutaneous nephrostomy• Percutaneous nephrolithotomy

NEH

ROLITH

IASIS

DEFINITION

Nephrolithiasis Presence of renal calculi.

Nephrocalcinosis Form of nephrolithiasis, characterised by

diffusely scattered foci of calcification in the renal parenchyma.

Stedman’s Concise Medical and Allied health dictionary. Third edition

“Kidney Stones” or “calculi” Composed of a combination of crystals (organic and

inorganic) and proteins

INCIDENCE 1.2 million Americans affected annually

Up to 14% of men and 6% of woman (M:V 3:1)

Any age: More than 1% < 18 years of age

Recurrence rate 50 % in 5-10 years 75% in 20 years

Annual health care burden (USA) $1.83 billion in 1993 $5.3 billion in 2000

CLASSIFICATION OF STONES Main role of Radiologist!! Important: will impact patient treatment and outcome!

Stone size <5mm; 5-10mm; 10-20mm; >20mm

Stone location Upper-,middle- or lower calyx Renal pelvis Upper-, middle- or distal ureter Bladder

X-ray characteristics Aetiology Stone composition Risk groups for stone formation

X-RAY CHARACTERISTICS

AETIOLOGY OF STONE FORMATION

COMPOSITION

RISK GROUPS FOR STONE FORMATION

FACTORS

INFLU

ENCIN

G TREATM

ENT

DECISIO

NS

SIZEAND

POSITION

PERCUTANEOUSNEPHROLITHOTOMY

±LASER

HU:<450 - Uric acid

600-900 - Struvite

600-1100 - Cystine 1200-1600 - Hydroxyapetite (Calcium phosphate)

1700-2800 - Clacium oxalate and Brushite (Calcium hydrogenphosphate)

COMPOSITION,AETIOLOGY

IMAG

ING

APPROACH

ADULTSUltrasound Primary investigation?

Varma G et al: Renal stones > 5mm - sensitivity 96%; specificity nearly

100% All stone locations - reduces to 78% and 31%.

Sandu et al: “US has limited diagnostic value in the assessment of patients

with suspected renal stones…. particularly in the evaluation of distal ureteral calculi “

Kidney-Ureter-Bladder radiograph (KUB) Sensitivity 44% to 77% and specificity 80% to 87%,

KUB not be done if NCCT considered.

Value: ?Radiopaque/radiolucent Follow up

Intravenous urography (IVU) Largely replaced by CT, MRI and US

Contraindications: General precautions to radiation and contrast agents (LOCM 370)

Dosages Adult: 50-100ml Paediatric: 1ml per kg

Technique1. KUB (Rapid injection of

bolus)2. 15sec-1min film = Nephrogram phase3. 5 min film = Excretion phase (apply band)4. 10 min film = Pelvi-ureteral phase (release band)5. Release film = Ureteral phase (empty

bladder)6. Coned bladder view/ Post-void KUB

Diagnosis of calculi on IVP

Nephrogram: Delayed or persistent due to ureteral obstruction

Column of opacified urine proximal to stone Minimal dilated Degree not related to stone size

Narrow ureter distal to calculus Oedema, inflammation False impression of stricture

“Steinstrasse” German for “stone street” or “street of stones” Several calculi are bunched up along ureter (common after

lithotripsy)

“Halo appearance” - oedema around distal ureter (>2mm) (<2mm = Pseudoureterocele)

IVU

Non Contrast-enhanced CT (NCCT)

Modality of choice sensitivity (95%–98%) and specificity (96%–100%)

Superior to IVU in diagnosis of stones.

Multidetector and Dual energy CT Multiplanar and 3D imaging – better accuracy All stones (except Indinavir and pure matrix stones) Density, size, position, tissue differentiation Stone-to-skin distance (ESWL) Identify other causes for pain.

Dalrymple et al - 55% of patients undergoing CT for acute flank pain did not have stones; 15% other abnormalities that was detected.

Drawback (NCCT) Renal function? Anatomy of collecting

system? Radiation

Reduce radiation by low-dose CT

100mAs; 120kv BMI <30 or weight <90 kg Dose similar to KUB study

-Kluner et al -Heneghan et al

Renal contrast study (CT or IVU) recommended when surgery is planned. CT preferred

Enables 3D reconstruction

Density/size Stone-to-skin

distance

MULTIDETECTOR CT Technique

No patient preparation

Entire urinary tract

Diagnosis: NCCT Workup: Contrast

study

Thinner (1–3mm) reconstructions recommended

- reduction in partial volume averaging effect. 5-mm scans/3-mm coronal

reformatted images - been found to improve stone detection while allowing radiation dose benefits

Signs of Nephrolithiasis Stone within urethral lumen Dilated proximal- and normal

calibre distal lumen Dilatation may be absent! Dalrymple et al: Urethral stones more likely in proximal (37%) and distal urethra (33%) in acute situation.

Secondary signs: Hydroureter Hydronephrosis Peri-nephric fat stranding Peri-urethral oedema Unilateral renal enlargement Contrast filling defect (Indinavir

stones!)

Stone within urethral lumen

Dilated proximal urethra

Secondary signs:HydronephrosisFat stranding

Renal enlargement

CALCULUS OR PHLEBOLITH?

CALCULUSANY SHAPE, HOMOGENOUS,

ALONG URETER“SOFT-TISSUE RIM SIGN”

PHLEBOLITHROUND, CENTRAL LUCENCY,

IN TRUE PELVIS“COMET TAIL SIGN”

STONE OR STENT?

FRAGILITY? HOMOGENEOUS VS HETEROGENEOUS

COMPOSITION? DUAL-ENERGY CT SCANNER

STONE-TO-SKIN DISTANCE

Magnetic Resonance urography (MRU)

Relative insensitive for detection of calcification

Relies on secondary signs of obstruction Ureteral dilatation Perinephric fluid Persistant “filling defect”

Technique dependant Excretory MR urography

IV gadolinium Sensitivities up to 90% reported

Static-fluid T2-weighted images T2 weighted technique Sequences

• HASTE• RARE

MRU

CHILDREN Ultrasound

First line imaging modality Practical technique No radiation or sedation

Information: Presence and size of

stones Location Degree of dilatation and

obstruction Cause

Nevertheless: Fail to identify stones in

40 % of patients No information on kidney

function

CHILDREN Plain films(KUB)

Identify stones Radio-opacity Facilitate follow up

Intravenous urography (IVU) Can be important tool Drawback: IV contrast

Magnetic resonance urography (MRU) “Filling defect” in T2 images Information:

Anatomy of collecting system Level of obstruction Morphology of renal parenchyma

Helical CT Radiation risk

Low-dose CT Reduced slices

5% of stones escape detection by non-enhanced helical CT Sedation or anaesthesia - rarely needed with modern high-speed

CT apparatus.

Nuclear medicine 99mTc-dimercaptosuccinyl acid scanning

information about cortical abnormalities (such as scarring) not for primary diagnosis of nephrolithiasis

Diuretic renogram Radiotracer (MAG3 or DPTA) and furosemide - used to

demonstrate: renal function identify obstruction indicate the anatomical level of the obstruction

CHILDREN

PREGNANCY Remains diagnostic and therapeutic challenge

Approach Ultrasound

Abdominal Transvaginal Endoluminal

Limited Excretory Urogram (IVU) for symptomatic patients

Preliminary KUB; 15min; 60min after contrast

MRU!! Static T2 images

ROLE IN

M

ANAG

EMEN

T

Antegrade pyelography Needle through renal parenchyma into

minor calyx (posterior lower pole preferred) Inject contrast to demonstrate

obstruction.

Percutaneous nephrostomy Introduction of drainage catheter into

collecting system of kidney. obstruction due to stone prior to percutaneous nephrolithotomy.

Percutaneous nephrolithotomy Removal of larger renal calculi through a

nephrostomy line. After series of dilatations; nephroscope

inserted Direct removal of stones <1cm Stone disintegration with US or

electrohydraulic disintegrator.

REFERENCES

1. http://www.uroweb.org/guidelines/online-guidelines/Guidelines on Urolithiasis. European Association of Urology 2011. C. Türk (chairman), T. Knoll (vice-chairman), A. Petrik, K. Sarica, M. Straub, C. Seitz

2. Kambadakone A, Eisner B, Catalano O, Sahani D. New and evolving concepts in the imaging and management of urolithiasis: Urologists’ Persapective. Radiographics 2010. 30: 603-623

3. Varma G, Nair N, Salim A, Marickar YM. Investigations for recognizing urinary stone. Urol Res. 2009 Dec;37(6):349-52.

4. Sandhu C, Anson KM, Patel U. Urinary tract stones I. Role of radiological imaging in diagnosis and treatment planning. Clin Radiol 2003;58(6): 415–421.

5. Dalrymple NC, Verga M, Anderson KR, et al. The value of unenhanced helical computerized tomography in the management of acute flank pain. J Urol 1998;159(3):735–740.

6. Kluner C, Hein PA, Gralla O, Hein E, Hamm B, Romano V, Rogalla P. Does ultra-low-dose CT with a radiation dose equivalent to that of KUB suffice to detect renal and ureteral calculi? J Comput Assist tomog. 2006 Jan-Feb; 30(1):44-50

7. Heneghan P, McGuire KA, Leder RA, DeLong DM, Yoshizumi T, Nelson RC. Helical CT for Nephrolithiasis and Ureterolithiasis: Comparison of Conventional and Reduced Radiation-Dose Techniques. Radiology. 2003: 229:575–580

8. Silverman SD, Leyendecker JR, Amis ES. What is the current role of CT urography and MR urography in the evaluation of the renal tract? Radiology 2009; 250: 309-323

9. Garcia-Valtuille R, Garcia-Valtuille L, Abascal F, Cerezal L, Arguello MC. Magnetic resonance urography: a pictorial overview. BJR 79 (2006), 614-626.

10. A guide to radiological procedures. Fifth edition. Frances Aitchison. Saunders puplishers.

11. Stedman’s concise medical and allied health dictionary. Third edition. Williams and Wilkins publisher.