Diagnostic Ultrasound - Abdomen and Pelvis
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Diagnostic Ultrasound - Abdomen and Pelvis

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Urolithiasis TERMINOLOGY Abbreviations • Ureterovesicular junction (UVJ); ureteropelvic junction (UPJ); intravenous pyelogram (IVP) Synonyms • Urinary tract stone, urinary calculous disease, nephrolithiasis, ureterolithiasis, vesicolithiasis Definitions • Macroscopic concretions of crystals in urinary system, sometimes mixed with proteins IMAGING General Features • Location ○ Renal stones: Upper pole, mid kidney (interpolar region), lower pole ○ Ureter stones: Can divide ureter into UPJ, proximal, mid, distal, and UVJ – Iliac vessels are an important landmark for treatment planning: Divide ureter into UPJ, proximal (UPJ to iliac vessels), distal (iliac vessels to UVJ), and UVJ ○ Bladder stones Ultrasonographic Findings • Grayscale ultrasound ○ Advantages: No ionizing radiation, inexpensive, accessible ○ Disadvantages: Operator dependent, deep ureter difficult to visualize, limited sensitivity for < 5 mm stone, overestimates stone size relative to CT, limited in obese patients ○ Calculi = echogenic foci with sharp posterior acoustic shadowing ○ For renal stones > 5 mm: 96% sensitivity, nearly 100% specificity ○ May be difficult to detect small, nonshadowing renal and ureteral calculi, unless there is obstruction – Most calculi missed by US are < 3 mm, which are more likely to pass spontaneously without intervention ○ Optimize technique – Fast for 4 hours to decrease bowel gas and hydrate to fill bladder – Maximize shadowing by placing single focal zone at or slightly deep to stone – Always include bladder with attention to UVJ □ Roll patient to show mobility of bladder calculus ○ Valuable for follow-up imaging, especially in patients with stones & renal colic or those not improving on treatment • Color Doppler ○ Twinkling artifact: Focus of alternating colors on color Doppler behind rough, reflective object – Helps ID otherwise occult stone that blends with renal sinus fat; more sensitive than acoustic shadowing – ↑ sensitivity compared with grayscale alone, but also ↑false-positives (up to 51%) ○ Should see ureteral jets intermittently and bilaterally – High-grade obstruction: Ureteral jet almost always absent – Low-grade obstruction: May (~ 1/3) or may not have absent ureteral jet □ Asymmetric decrease or continuous low-amplitude jet on affected side Radiographic Findings • Radiography ○ ~ 90% of calculi are radiopaque; calcium stones > struvite & cystine stones – More sensitive than CT scout image (63% vs. 47%) – Valuable for planning treatment (e.g., ESWL) & monitoring stone burden – Disadvantages: Limited sensitivity (~ 60%); limiting factors: Bowel gas, extrarenal calcification, obesity ○ Radiolucent: Uric acid, xanthine, pure matrix, drug stones, 2,8-dihydroxyadenine • IVP ○ Formerly study of choice; has been replaced by CT ○ Fails to detect calculi in 31-48% of cases CT Findings • NECT ○ Preferred imaging modality to confirm stone in adult patients with acute flank pain ○ Virtually all stones are visible (including those radiolucent on KUB) except pure matrix stones and protease inhibitor stones (e.g., indinavir) ○ Advantages: Fast, no IV contrast, high sensitivity (nearly 100%), allows detection of unsuspected abnormalities, useful for treatment planning ○ CT attenuation measurements (highest to lowest) for evaluating stone composition – Calcium oxalate monohydrate and brushite (1700- 2800 HU) – Calcium phosphate (1200-1600 HU) – Cystine (600-1100 HU) – Struvite (600-900 HU) – Uric acid (200-450 HU) – 35-65% of stones are of mixed composition; CT attenuation measurements most valuable in differentiating 100% uric acid stones from others ○ Ureterolithiasis – Direct sign: Visualization of calculus within ureteral lumen; ureteral dilation may be absent – Secondary signs: Most reliable: Hydroureter/hydronephrosis, perinephric stranding, periureteral edema, and unilateral renal enlargement – "Soft tissue rim" sign = ureteral stone: Soft tissue halo around calcific focus = ureteral wall edema around stone; highly specific (≥ 90%) for ureteral stone – "Comet tail" sign = phlebolith: Eccentric, tapering soft tissue density adjacent to calcification = noncalcified portion of pelvic vein and phlebolith; specificity nearly 100% for phlebolith – Phlebolith: Central lucency, calculus, nearly all are centrally dense ○ Best way to measure stone size is with bone windows and magnification ○ Randall plaque = stone precursor; subepithelial calcification seen as whitish build-up in papillary tips Diagnoses: Urinary Tract 449

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 450 CLINICAL ISSUES Presentation • Most common signs/symptoms

Urolithiasis<br />

TERMINOLOGY<br />

Abbreviations<br />

• Ureterovesicular junction (UVJ); ureteropelvic junction<br />

(UPJ); intravenous pyelogram (IVP)<br />

Synonyms<br />

• Urinary tract stone, urinary calculous disease,<br />

nephrolithiasis, ureterolithiasis, vesicolithiasis<br />

Definitions<br />

• Macroscopic concretions of crystals in urinary system,<br />

sometimes mixed with proteins<br />

IMAGING<br />

General Features<br />

• Location<br />

○ Renal stones: Upper pole, mid kidney (interpolar region),<br />

lower pole<br />

○ Ureter stones: Can divide ureter into UPJ, proximal, mid,<br />

distal, <strong>and</strong> UVJ<br />

– Iliac vessels are an important l<strong>and</strong>mark for treatment<br />

planning: Divide ureter into UPJ, proximal (UPJ to iliac<br />

vessels), distal (iliac vessels to UVJ), <strong>and</strong> UVJ<br />

○ Bladder stones<br />

Ultrasonographic Findings<br />

• Grayscale ultrasound<br />

○ Advantages: No ionizing radiation, inexpensive,<br />

accessible<br />

○ Disadvantages: Operator dependent, deep ureter<br />

difficult to visualize, limited sensitivity for < 5 mm stone,<br />

overestimates stone size relative to CT, limited in obese<br />

patients<br />

○ Calculi = echogenic foci with sharp posterior acoustic<br />

shadowing<br />

○ For renal stones > 5 mm: 96% sensitivity, nearly 100%<br />

specificity<br />

○ May be difficult to detect small, nonshadowing renal <strong>and</strong><br />

ureteral calculi, unless there is obstruction<br />

– Most calculi missed by US are < 3 mm, which are more<br />

likely to pass spontaneously without intervention<br />

○ Optimize technique<br />

– Fast for 4 hours to decrease bowel gas <strong>and</strong> hydrate to<br />

fill bladder<br />

– Maximize shadowing by placing single focal zone at or<br />

slightly deep to stone<br />

– Always include bladder with attention to UVJ<br />

□ Roll patient to show mobility of bladder calculus<br />

○ Valuable for follow-up imaging, especially in patients<br />

with stones & renal colic or those not improving on<br />

treatment<br />

• Color Doppler<br />

○ Twinkling artifact: Focus of alternating colors on color<br />

Doppler behind rough, reflective object<br />

– Helps ID otherwise occult stone that blends with renal<br />

sinus fat; more sensitive than acoustic shadowing<br />

– ↑ sensitivity compared with grayscale alone, but also<br />

↑false-positives (up to 51%)<br />

○ Should see ureteral jets intermittently <strong>and</strong> bilaterally<br />

– High-grade obstruction: Ureteral jet almost always<br />

absent<br />

– Low-grade obstruction: May (~ 1/3) or may not have<br />

absent ureteral jet<br />

□ Asymmetric decrease or continuous low-amplitude<br />

jet on affected side<br />

Radiographic Findings<br />

• Radiography<br />

○ ~ 90% of calculi are radiopaque; calcium stones > struvite<br />

& cystine stones<br />

– More sensitive than CT scout image (63% vs. 47%)<br />

– Valuable for planning treatment (e.g., ESWL) &<br />

monitoring stone burden<br />

– Disadvantages: Limited sensitivity (~ 60%); limiting<br />

factors: Bowel gas, extrarenal calcification, obesity<br />

○ Radiolucent: Uric acid, xanthine, pure matrix, drug<br />

stones, 2,8-dihydroxyadenine<br />

• IVP<br />

○ Formerly study of choice; has been replaced by CT<br />

○ Fails to detect calculi in 31-48% of cases<br />

CT Findings<br />

• NECT<br />

○ Preferred imaging modality to confirm stone in adult<br />

patients with acute flank pain<br />

○ Virtually all stones are visible (including those radiolucent<br />

on KUB) except pure matrix stones <strong>and</strong> protease<br />

inhibitor stones (e.g., indinavir)<br />

○ Advantages: Fast, no IV contrast, high sensitivity (nearly<br />

100%), allows detection of unsuspected abnormalities,<br />

useful for treatment planning<br />

○ CT attenuation measurements (highest to lowest) for<br />

evaluating stone composition<br />

– Calcium oxalate monohydrate <strong>and</strong> brushite (1700-<br />

2800 HU)<br />

– Calcium phosphate (1200-1600 HU)<br />

– Cystine (600-1100 HU)<br />

– Struvite (600-900 HU)<br />

– Uric acid (200-450 HU)<br />

– 35-65% of stones are of mixed composition; CT<br />

attenuation measurements most valuable in<br />

differentiating 100% uric acid stones from others<br />

○ Ureterolithiasis<br />

– Direct sign: Visualization of calculus within ureteral<br />

lumen; ureteral dilation may be absent<br />

– Secondary signs: Most reliable:<br />

Hydroureter/hydronephrosis, perinephric str<strong>and</strong>ing,<br />

periureteral edema, <strong>and</strong> unilateral renal enlargement<br />

– "Soft tissue rim" sign = ureteral stone: Soft tissue halo<br />

around calcific focus = ureteral wall edema around<br />

stone; highly specific (≥ 90%) for ureteral stone<br />

– "Comet tail" sign = phlebolith: Eccentric, tapering soft<br />

tissue density adjacent to calcification = noncalcified<br />

portion of pelvic vein <strong>and</strong> phlebolith; specificity nearly<br />

100% for phlebolith<br />

– Phlebolith: Central lucency, calculus, nearly all are<br />

centrally dense<br />

○ Best way to measure stone size is with bone windows<br />

<strong>and</strong> magnification<br />

○ R<strong>and</strong>all plaque = stone precursor; subepithelial<br />

calcification seen as whitish build-up in papillary tips<br />

Diagnoses: Urinary Tract<br />

449

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