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Radiologists’ role in nephrolithiasis. May 2012 Dr W.J. Conradie Department of Diagnostic Radiology. Nephrolithiasis Definition Incidence Classification Factors influencing treatment decision Imaging approach Adults Children Pregnancy R ole in management Antegrade pyelography - PowerPoint PPT Presentation
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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.