Diagnostic Ultrasound - Abdomen and Pelvis

Urolithiasis
Diagnoses: Urinary Tract
• CECT
○ CT lucent stones →filling defects
○ In select cases, CT IVP may help differentiate distal
ureteral stone from phlebolith
• Dual-energy CT (DECT): Scanning at different energies (80
and 140 kVp) allows better stone characterization
○ Can differentiate: Urate stones from other stones;
struvite from cystine stones→ both relevant for
treatment planning
MR Findings
• Virtually all stones = signal voids
• Ureteral calculi: Abrupt change in ureter caliber indicates
obstruction level; secondary signs
DIFFERENTIAL DIAGNOSIS
Nephrocalcinosis (NC)
• Calcification within parenchyma: Medullary NC (most
common) & cortical NC
• Often associated with urolithiasis
Papillary Necrosis
• Calcified sloughed papilla
• Nonshadowing echoes within medullary cavities; empty
medullary cavities after passed sloughed papilla
Emphysematous Pyelonephritis (EP), Pyelitis
• Gas within renal parenchyma (pyelonephritis) or renal
collecting system (pyelitis) with dirty shadowing
PATHOLOGY
General Features
• Etiology
○ Exact mechanism is unknown, but concept of urinary
supersaturation is essential
○ Low urine volume/dehydration (most common)
○ Metabolic: Commonly hypercalciuria,
hyperuricosuria,hypocitraturia, hyperoxaluria
○ Urine composition: pH, crystal inhibitors, stone-forming
substances
○ Disease states: Obesity, RTA type 1, IBD, medullary
sponge kidney, sarcoid, etc.
○ UTI, including urease-producing bacteria (Klebsiella,
Proteus, Pseudomonas, some Staphylococci)
○ Sedentary lifestyle, immobilization
○ Anatomic: Urinary obstruction or stasis
○ Medications: Protease inhibitors (Indinavir), supplements
(e.g., ephedrine), triamterene, sulfonamides
• Types of stones
○ Calcium-based stones (70-80%): Calcium oxalate
monohydrate and dihydrate, calcium phosphate
○ Struvite (5-15%): Magnesium ammonium phosphate
○ Uric acid (5-10%)
○ Cystine (1-2.5%)
○ Other (< 5%): Xanthine, matrix, drugs,2,8-
dihydroxyadenine
○ Acute flank pain, renal colic
○ Associated symptoms: Microscopic or gross hematuria,
nausea, and vomiting
Demographics
• Gender
○ M > F
• Epidemiology
○ Up to 14% of men and 6% of women develop stones
Natural History & Prognosis
• Spontaneous ureteral stone passage based on size
○ > 8 mm rarely pass without intervention
○ 95% of stones up to 4 mm pass within 40 days
• Complications: Obstruction, infection, and renal
insufficiency
• Recurrence rate is ~ 75% over 20 years
Treatment
• Options for upper tract urolithiasis
○ Surveillance (trial of passage): Hydration & pain relief;
medical expulsive therapy (MET)
○ Extracorporeal shock wave lithotripsy (ESWL)
○ Ureteroscopy and endoscopic lithotripsy (URS)
○ Percutaneous nephrolithotomy (PCNL)
○ Dissolution (chemolysis)
○ Open or laparoscopic surgery
• Size, number, location, obstruction or infection, and
anatomic findings (aberrant vasculature, distorted
pelvicalyceal architecture) all impact treatment
○ Urate stones (< 450 HU): Only stones efficiently treated
with oral chemolysis (alkalinization)
○ CT findings that ↓ success of ESWL: Lower pole stone
location, larger stone size, high-attenuation (> 1000 HU)
and cystine stones, larger stone-to-skin distance
○ > 1000 HU→ URS or PCNL
• For renal stones: 0.5-1.5 cm stones → increasing popularity
of URS due to high stone-free rates
○ < 1 cm: Asymptomatic →observation; symptomatic→
SWL or URS
○ 1-2 cm→ SWL or PCNL
○ > 2 cm or staghorn→ PCNL
– Staghorn calculi →progressive renal damage and
persistent infection; treatment goal: Complete stone
removal
• For ureteral stones: < 10 mm→ MET or SWL, URS; > 10
mm→ SWL or URS
SELECTED REFERENCES
1. Spettel S et al: Using Hounsfield unit measurement and urine parameters to
predict uric acid stones. Urology. 82(1):22-6, 2013
2. Cheng PM et al: What the radiologist needs to know about urolithiasis: part
2--CT findings, reporting, and treatment. AJR Am J Roentgenol.
198(6):W548-54, 2012
3. Cheng PM et al: What the radiologist needs to know about urolithiasis: part
1--pathogenesis, types, assessment, and variant anatomy. AJR Am J
Roentgenol. 198(6):W540-7, 2012
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CLINICAL ISSUES
Presentation
• Most common signs/symptoms