imaging of renal calculi - acurity · • on ct calculi are hyper-dense foci within the renal...
TRANSCRIPT
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Dr Rodney Wu
IMAGING OF RENAL CALCULI
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• Obstructing renal or ureteric calculus most frequent
cause of flank pain, but flank pain is a non specific
symptom
• Seen in 35-55% of patients who undergo imaging for
pain
• Lifetime risk of urinary calculus 12% for men and 6%
for women
• Incidence increases with age until age 60
• Spontaneous passage is size dependent and
inversely proportional to size. Calculus <5mm has
68% probability of spontaneous passage.
IMAGING OF RENAL CALCULI
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IMAGING MODALITIES
• Xray
• Ultrasound
• IVP
• Xray and Ultrasound
• CT
• MRI
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• Sensitivity 58-62% renal or ureteric
• Accuracy 61%
• Surgical planning, stent placement, follow-
up calculus
• Gives no information about hydronephrosis
• Digital radiography 72% sensitive for >5mm
calculi proximal ureter but only 29% overall
for stone detection stones of any size
• Dose 0.8mSv compared with 10-12 mSv
conventional NCCT and 3-4 mSv low dose
CT KUB
XRAY
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IVP
• Provides physiologic information
• Degree of delayed nephrogram is related to the
severity of obstruction
• Sensitivity 85% Accuracy 92%
• Similar dose to low-dose NCCT (3.6mSv) and
requires IV contrast
• Can take several hours to complete if obstruction and
misses 31-48% of stones
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ULTRASOUND
• Can assess for dilatation of collecting system without
use of radiation
• Sensitivity 24-57% (renal/ureteral calculus) 73-86% (if
secondary signs of obstruction such as
hydronephrosis or lack of ureteric jet in bladder )
• Hydronephrosis can take hours to develop and varies
with degree of hydration
• Accuracy 69%
• Calculus is echogenic focus with posterior acoustic
shadowing. Best visualised when calculus >5mm
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• Twinkle artifact is an intense multicoloured signal
posterior to a stone with colour doppler . Distinguish
between stones <5mm and vascular calcifications.
High false –positive rate
• Absence of a unilateral ureteral jet within the bladder
can support the presence of obstruction however the
patient needs to be well hydrated
• Jet can still be present with partial obstruction
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XRAY AND ULTRASOUND
• Prospective study 66 pts comparing CT with KUB/US
revealed all stones not detected by KUB/US passed
spontaneously
• US in initial ED flank pain evaluation does not
increase the rate of adverse events or return ED visits
• However 27-41% of pts who initially had US required
a subsequent CT
• Sensitivity 79% (v 93% for NCCT)
• Accuracy 71%
• Advantages: US is lack of ionising radiation
• Disadvantages: needs skilled personnel, inability to
accurately measure stone size, need to observe
ureteral jet phenomenon at the VUJ (takes time) and
inability to distinguish dilatation without obstruction
from true obstruction
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CT
• Non contrast CT (NCCT) initial study for evaluating
flank pain since 1995
• Sensitivity 95% Accuracy 98%
• Virtually all stones radio-opaque on CT and size can
be measured
• Fast readily available, provides over view of
abdomen, stone burden and precise location
• Concerns over radiation exposure have led to
reduced –dose CT regimens
• Lower kVp, lower tube current, automated tube
current modulation and iterative reconstruction
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• On CT calculi are hyper-dense foci within the renal
collecting system, ureter or bladder
• Differential diagnosis for a calculus is a phlebolith
within gonadal or pelvic vein
• Comet tail sign: tapering soft tissue=non calcified
portion of the vein
• Tissue rim sign: oedematous ureteric wall surrounding
ureteral stone
• Calculi often lodge at the 3 narrowest segments of the
ureter 1. PUJ 2. crossing the iliac vessels 3. VUJ
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TISSUE RIM SIGN PHLEBOLITH
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PUJ CALCULUS
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ILIAC VESSELS
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VUJ CALCULUS
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DO YOU NEED IV CONTRAST?
• Miller and colleagues study to evaluate utility of IV
contrast in flank pain assessment
• 708 pts received contrast 43 (6%) had findings that
required IV contrast, 32 of those had pyelonephritis
• 8 patients had renal cell carcinoma, 6 of whom had
masses large enough to see without IV contrast
• Specific indications for IV contrast in patients who
present with flank pain include unilateral renal
stranding /enlargement with risk factors for renal
infarct or vein thrombosis, perirenal collection, renal
mass/complicated cyst or unexplained haematuria
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PARAPELVIC CYSTS
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URETERIC CALCULUS V PHLEBOLITH?
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DUAL ENERGY CT RENAL STONE CHARACTERIZATION
• Two different CT data sets at two different energy
levels.
• DECT takes advantage of the unique absorption
characteristics of urinary stone subtypes at high and
low energy xrays allowing composition
characterization.
• Benefits the patient by directing treatment at the time
of initial stone detection. 50% of patients will
experience recurrent stone disease after treatment.
• Treatment ranges from medical management to a
variety of non-invasive and invasive urologic
techniques.
•
• Differentiation between uric acid (UA) and non-UA
(commonly calcium containing) renal stones.
• UA calculi comprise 10% of stone disease and
typically treated medically using urinary alkalization
with stone dissolution.
• Characterization of additional stone types other than
UA is important to patient management as stones
known to be resistant to extracorporeal shock wave
lithotripsy (cysteine,brushite or calcium oxalate) can
be directed to management with percutaneous or
endoscopic stone removal
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• Tailored approach: Initial low dose NCCT followed by
limited unenhanced dual-energy CT through identified
calculi.
• Calcium based 75%
• Struvite 15%
• Uric acid 8%
• Cysteine 3%
• Only 1/3 of calculi are pure stones, 44% contain 2
components, 25% contain 3 or more components.
Characterization of mixed stone types more
challenging than pure stone types.
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INDICATION CREEP: 16-45%
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PYELONEPHRITIS
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DIVERTICULITIS HAEMORRHAGIC RENAL CELL CARCINOMA
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MRI
• Examination of choice for hydronephrosis in
pregnancy
• Alternative to low-dose NCCT in certain patient
populations such as pregnant women (non contrast
MRI), young individuals and individuals who have
undergone multiple prior CTs
• Sensitivity 50-60%(renal/ureteral calculi) 100% (if
there are 2nd signs of obstruction)
• MRI highly accurate for diagnosis of hydronephrosis
and perinephric oedema but less accurate in directly
visualizing stones compared to NCCT
• MRI visible stones measured on average 11mm and
stones not visible measured an average of 4.6mm
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ACUTE FLANK PAIN-SUSPICION OF STONE DISEASE
• Suspicion of stone disease
• Recurrent symptoms of stone disease
• Suspicion of stone disease pregnant patient
• ACR appropriateness criteria
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ACUTE FLANK PAIN-SUSPICION OF STONE DISEASE
• Suspicion of stone disease
• Recurrent symptoms of stone disease
• Suspicion of stone disease pregnant patient
• Non contrast CT: most rapid and accurate
• Ultrasound recommended initial modality for flank
pain in young women (<45 years)
• Young women lower rate of stone detection than men
(24% v 62%) due to gynaecologic causes for pain
• Organ dose for ovaries is higher due to position
• 83% of women with stones larger than 4mm have
hydronephrosis therefore KUB/US initial modality for
young women
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ACUTE FLANK PAIN-SUSPICION OF STONE DISEASE
• Suspicion of stone disease
• Recurrent symptoms of stone disease
• Suspicion of stone disease pregnant patient
• KUB/US
• Likelihood of urolithiasis as cause of flank pain is
higher but repeated NCCT raise concern about
excessive radiation
• If previously documented stones seen on KUB, a
repeat KUB provides useful information at lower dose
• KUB can follow stones visible on scout radiograph of
a CT. Stones not visible on scout may not be visible
on KUB
• KUB can assess stone burden and position of stones
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ACUTE FLANK PAIN-SUSPICION OF STONE DISEASE
• Suspicion of stone disease
• Recurrent symptoms of stone disease
• Suspicion of stone disease pregnant patient
• MRI or US : First trimester
• CT : Second or third trimester
• Pregnant women physiologic right hydronephrosis is a
confounding phenomenon in 2nd trimester. Occurs
secondary to obstruction of right distal ureter by
gravid uterus
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SUMMARY
• Low-dose NCCT most accurate modality for
evaluating flank pain
• If uncertainty whether calcific density represents a
ureteral stone or phlebolith IV contrast can be
administered and excretory phase images obtained
• Pregnant patients with flank pain US best modality
• KUB/US may be able to diagnose most clinically
significant stones consider in young patients and
those with known stone disease
• MRI can evaluate for hydronephrosis though is less
accurate for direct visualization of renal and ureteral
stones
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• Abdominal xray $111
• Renal ultrasound $247
• CT KUB $715
• Renal CT with IV contrast $1167