Ureteric Stone (Ureteral Calculus) - A Comprehensive Review

I. DEFINITION AND EPIDEMIOLOGY

• Lifetime risk of stone disease: ~9% (Sabiston)
• Male:Female ratio = 2:1
• Peak age: 4th to 6th decade
• Most common site of ureteric impaction: vesicoureteric junction (VUJ) > pelviureteric junction (PUJ) > crossing of iliac vessels

II. ETIOPATHOGENESIS

A. Stone Types and Frequency

B. Pathogenesis

1. Supersaturation → crystal nucleation → aggregation → stone growth
2. Promoters of crystallization: calcium, oxalate, uric acid, low urine volume, acidic/alkaline pH
3. Inhibitors of crystallization (when deficient): citrate, pyrophosphate, magnesium, glycoproteins (nephrocalcin, Tamm-Horsfall protein)

C. Specific Stone Mechanisms

• Hypercalciuria (most common) - caused by:
  • Absorptive hypercalciuria (excess intestinal Ca absorption)
  • Renal hypercalciuria (impaired tubular Ca reabsorption)
  • Hypercalcemia: hyperparathyroidism, sarcoidosis, bone disease
• Hyperoxaluria: primary (hereditary) or enteric (Crohn's disease, short gut)
• Hyperuricosuria (20%): uric acid crystals nucleate calcium oxalate
• Hypocitraturia: loss of inhibition
• Idiopathic (15-20%)

• Urease-producing organisms (Proteus mirabilis, Klebsiella, Staph) split urea → ammonia → alkaline urine → magnesium ammonium phosphate precipitates
• Form largest stones ("staghorn calculi")

• Gout, hyperuricemia, high cell turnover (leukemia)
• Uric acid insoluble at pH <5.5 → acidic urine is the key factor

• 50% have neither hyperuricemia nor hyperuricosuria

• Autosomal recessive defect in renal tubular reabsorption of COLA amino acids (Cystine, Ornithine, Lysine, Arginine)
• Form at low pH

III. CLINICAL FEATURES

A. Symptoms

• Severe, colicky flank/loin pain radiating to the groin, labia/scrotum, inner thigh
• Pain waxes and wanes but cannot be resolved by position change
• Nausea, vomiting, ileus (visceral distension from proximal obstruction)

• PUJ stone → loin pain, iliac fossa pain
• Mid-ureteric stone → pain radiates to the groin
• VUJ stone → bladder irritability: frequency, urgency, dysuria, testicular/labial pain

• Hematuria (gross or microscopic) - seen in 90%
• Low-grade fever (if infection coexists)
• Signs of sepsis (fever >38.5°C, hypotension, tachycardia) = urological emergency

B. Signs

• Loin tenderness, renal angle tenderness (costovertebral angle)
• Guarding in the flank
• Patient is restless, cannot find a comfortable position (unlike peritonitis where patient lies still)

C. Investigations

1. Urine: Hematuria, pyuria, pH (acidic = uric acid; alkaline = struvite)
2. Blood: CBC (leukocytosis), urea/creatinine (renal function), serum calcium, uric acid
3. Imaging:
   • X-ray KUB: 85% of stones radiopaque; identifies position, number
   • Ultrasound: Hydronephrosis, proximal dilatation; limited for mid-ureteric stones
   • Non-contrast CT (NCCT) KUB: Gold standard - sensitivity 95-98%, specificity 96-100%; detects all stone types including radiolucent; determines size, location, density (Hounsfield units)
   • IVU (Intravenous Urogram): Obstruction, "standing column" of contrast, site of impaction
   • MR Urography: For pregnancy (no radiation)

IV. PRINCIPLES OF MANAGEMENT

A. Conservative / Expectant Management

• Analgesia: IV NSAIDs (diclofenac, ketorolac) - first line; reduce ureteric spasm and prostaglandin-mediated inflammation; opioids as second line
• Hydration: Maintain good urine output
• Medical Expulsive Therapy (MET):
  • Alpha-blockers (Tamsulosin 0.4 mg/day): Relax ureteric smooth muscle, especially at VUJ → most effective for distal ureteric stones; increases passage rate by ~30%
  • Calcium channel blockers (nifedipine): reduce dysmotive contractions
• Expected passage rates: <5 mm - 90%; 5-10 mm - 50%; >10 mm - <10%
• Follow-up reimaging to confirm passage

• Obstructing stone + UTI / urosepsis → urological emergency
• Pyonephrosis
• Solitary kidney with obstruction
• Bilateral obstruction with renal failure

V. DIFFERENT TREATMENT MODALITIES

1. EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY (ESWL)

• Stone ≤2 cm in maximum diameter
• Proximal ureteric stones (≤1 cm)
• No distal obstruction
• Kidney function present

• Non-invasive, no anesthesia required (sedation/LA)
• Outpatient procedure
• Safe in most patients including elderly

• Multiple sessions may be needed
• Lower stone-free rate vs ureteroscopy for distal stones
• Contraindicated in pregnancy, coagulopathy, pacemaker
• Steinstrasse (stone street) - obstructing fragments after fragmentation
• Radiolucent stones (uric acid) harder to target (unless fluoroscopy or US-guided)
• Not ideal for hard stones (calcium oxalate monohydrate, cystine)
• Failure rate higher for stones >1 cm in ureter

2. URETEROSCOPY (URS) - See Section VI for full endoscopic details

3. PERCUTANEOUS NEPHROLITHOTOMY (PCNL) / ANTEROGRADE URETEROSCOPY

• Large, impacted proximal ureteric stone >1.5-2 cm
• Failed ESWL or URS
• Reimplanted ureters, reconstructed bladders
• Anatomical abnormality preventing retrograde access

4. LAPAROSCOPIC / OPEN URETEROLITHOTOMY

• Large, impacted stone >1.5 cm not amenable to endoscopic treatment
• Failed ESWL and URS
• Associated ureteric pathology needing repair (stricture, UPJ obstruction)
• Stones in a reimplanted ureter

VI. ENDOSCOPIC MANAGEMENT OF URETERIC STONES

A. Ureteroscopy - Overview

B. Types of Ureteroscopes

C. Intracorporeal Lithotripsy Devices

• Wavelength: 2140 nm
• Mechanism: Photothermal - absorbed by water layer on stone surface, creating a vapor bubble (Moses effect) that fragments stone
• Fiber sizes: 200-365 µm (200 µm for flexible, 365 µm for semi-rigid)
• Fragmentation modes:
  • Dusting: Low energy (0.2 J), high frequency (40 Hz) → fine dust, no basket needed
  • Fragmentation: Higher energy → larger pieces, basket extraction
• Stone-free rate: 95-97% for ureteric stones (laser superior to pneumatic)

• Uses compressed air or gas to fire a metal probe at the stone
• Probe sizes: 2.4-Fr
• Effective for semi-rigid URS; energy lost when probe is bent (flexible URS inefficient)
• Retropulsion risk: 10% distal, 40% proximal - major limitation
• Stone-free rate: ~85-91%

• Electrical discharge creates plasma spark → concentric shockwave + cavitation bubble
• Risk of ureteric perforation at >1000 mJ
• Use confined to semi-rigid; cannot be used with flexible scope safely at high energies
• No longer commonly used

• Piezoelectric probe vibrates at ultrasonic frequency
• Simultaneous suction removes fragments
• Used mainly in nephroscopy (PCNL); less used in ureteroscopy

D. Procedure (Semi-rigid URS - Stepwise)

1. Cystoscopy + guide wire insertion up the ureter
2. Ureteric access (dilation if needed or ureteric access sheath)
3. Semi-rigid ureteroscope advanced alongside / over wire
4. Stone visualized
5. Laser fiber / probe inserted through working channel
6. Stone fragmented
7. Fragments retrieved with Dormia basket or forceps
8. JJ stent placement (optional - see below)

E. Ureteric Access Sheath (UAS)

• 10-13 Fr sheath placed over guide wire before flexible URS
• Allows easy re-entry, reduces intrarenal pressure, improves irrigation/visibility
• Slight risk of ureteric mucosal injury

F. Anti-Retropulsion Devices

• Stone Cone, N-Trap, BackStop, Accordion, Parachute - devices placed proximal to stone to prevent migration
• Reverse Trendelenburg positioning (2024 meta-analysis confirmed benefit for proximal stones - PMID 38849037)
• Basket stabilization
• Lidocaine gel instillation

G. JJ Stent Post-Ureteroscopy

• Indications: ureteric edema, perforation, single kidney, poor drainage, large stone burden
• Duration: 2-4 weeks typically
• Drawbacks: stent symptoms (frequency, urgency, flank pain), bladder irritation

H. Advantages of Ureteroscopy

• High stone-free rates: 95-97% for distal stones, 80-91% for proximal
• Single session success in most cases
• Applicable to all stone types including radiolucent (uric acid, cystine)
• Safe in pregnancy, anticoagulated patients, bleeding disorders
• Allows stone retrieval AND analysis of composition (basket extraction)
• Can be used when ESWL fails or is contraindicated
• Diagnostic advantage: direct visualization of ureteric mucosa
• Applicable in anomalous anatomy (horseshoe kidney, transplant ureter)
• Can be done under spinal or general anesthesia

I. Disadvantages of Ureteroscopy

• Requires general/spinal anesthesia (vs ESWL)
• Ureteric injury risk: perforation, avulsion (rare), false passage
• Ureteric stricture: delayed complication from mucosal damage
• Retropulsion (especially pneumatic lithotripsy)
• Intraoperative failure if scope cannot pass (tight ureteric orifice → prestenting required)
• Post-procedure stent symptoms (if stent placed)
• Requires fluoroscopy and specialized equipment
• Flexible ureteroscope: fragile, expensive, high maintenance; limited number of uses
• Infective complications: UTI, sepsis if obstructed infected system treated aggressively
• More invasive than ESWL

J. Outcomes by Stone Location

VII. RECENT MODALITIES OF TREATMENT

1. Thulium Fiber Laser (TFL)

• Wavelength: 1940 nm (closer to water absorption peak than Ho:YAG)
• Advantages over Ho:YAG:
  • 4x more efficient water absorption → more efficient stone vaporization
  • Higher repetition rates (up to 2200 Hz vs 80 Hz for Ho:YAG)
  • Smaller fiber diameters possible (50-100 µm) → less scope deflection impairment
  • Superior dusting ability, less retropulsion
  • Better hemostatic properties
• Currently gaining widespread adoption as the next-generation laser
• FDA cleared; clinical trials show non-inferiority/superiority to Ho:YAG in stone-free rates

2. "Moses Technology" (Pulsed-Modulated Ho:YAG)

• Modified pulse delivery creates a vapor channel ("Moses effect") before stone contact
• Results in: more efficient energy delivery, less retropulsion, faster fragmentation
• Available on newer Ho:YAG platforms (Lumenis MOSES)

3. Single-Use Flexible Ureteroscope

• Disposable flexible ureteroscopes (e.g., LithoVue, Uscope, Ureovision)
• Eliminate need for repair/reprocessing of expensive reusable scopes
• Maintain consistent optical quality
• Reduce infection risk from reprocessing failures
• Increasingly adopted globally

4. Robotic-Assisted Ureteroscopy

• Robotic platforms (Avicenna Roboflex, Urobot) allow remote-controlled flexible ureteroscopy
• Reduces radiation exposure to surgeon
• Tremor-free manipulation; potentially improves precision
• Still in early adoption phase

5. Miniaturized PCNL (Mini-PCNL, Ultramini-PCNL, Micro-PCNL)

• Percutaneous access using smaller sheaths (10-14 Fr vs standard 24-30 Fr)
• Mini-PCNL (14-20 Fr), Ultramini-PCNL (11-13 Fr), Micro-PCNL (4.85 Fr)
• Applicable for large proximal ureteric/renal pelvic stones when URS fails
• Less bleeding, smaller nephrostomy tract, shorter hospital stay vs standard PCNL
• Stone-free rates comparable to standard PCNL

6. CT-Guided / Fluoroscopy-Free Procedures

• Ultrasound-guided ureteroscopy and ESWL targeting
• Reduces radiation exposure to patient and surgeon

7. "Dusting" Strategy with High-Frequency Laser

• Technique refinement: high-frequency, low-energy Ho:YAG or TFL produces fine powder
• Particles <150 µm pass spontaneously without basket extraction
• Stentless procedure in many cases → saves stent-related morbidity

8. Medical Dissolution Therapy (for Uric Acid Stones)

• Urinary alkalinization with potassium citrate/sodium bicarbonate (target urine pH 6.5-7.0)
• Oral allopurinol (reduce uric acid production)
• Can dissolve uric acid stones non-invasively over weeks
• Applicable only for pure or predominant uric acid stones (confirmed by NCCT Hounsfield units <500 HU and radiolucency on KUB)

VIII. MANAGEMENT SUMMARY BY STONE POSITION

IX. COMPLICATIONS OF UNTREATED URETERIC STONES

• Hydronephrosis → hydroureteronephrosis
• Urosepsis / pyonephrosis
• Renal cortical atrophy and loss of function
• Ureteric stricture at site of impaction
• Xanthogranulomatous pyelonephritis (chronic obstruction + infection)