Urinary Tract Obstruction and Stones

Urinary Tract Obstruction and Stones - Blockage Blues

• Obstruction (UTO): Impeded urine flow.
  • Sites: Pelviureteric junction (PUJ), pelvic brim, vesicoureteric junction (VUJ), urethra.
  • Causes: Stones, strictures, BPH, tumors.
  • Results in: Hydronephrosis, infection, ↓renal function.
• Stones (Urolithiasis):
  • Types:
    • Calcium Oxalate/Phosphate (~75-80%): Most common, radiopaque.
    • Struvite (MAP): Infection (Proteus), staghorn, radiopaque.
    • Uric Acid: Radiolucent, gout, acidic urine.
    • Cystine: Rare, genetic, faintly opaque.
  • Symptoms: Renal colic, hematuria.

⭐ Posterior urethral valves are the most common cause of UTO in male infants.

Urinary Tract Obstruction and Stones - Pressure Problems

• Sustained UTO elevates intraluminal pressure, causing progressive dilation.
  • Hydronephrosis: Dilation of renal pelvis and calyces, leading to renal parenchymal compression and atrophy.
  • Hydroureter: Dilation of the ureter proximal to the site of obstruction.
• Pathophysiology:

• Key Consequences:
  • Progressive loss of renal mass; interstitial inflammation.
  • Impaired tubular function: ↓ concentrating ability, electrolyte imbalances.
  • Reduced renal blood flow contributes to ischemic injury.
• Irreversible damage: Possible within ~3-4 weeks for complete obstruction; months for partial.

⭐ Bilateral complete obstruction can lead to anuria and rapid renal failure; irreversible damage may occur within weeks.

Urinary Tract Obstruction and Stones - Rocky Road

• Pathogenesis: Supersaturation of urine with stone-forming salts → Crystal nucleation → Aggregation → Growth → Stone.
• Types & Key Features:
  • Calcium Oxalate (70-80%): Most common. Radiopaque. Envelope/dumbbell crystals. Risk: Hypercalciuria, hyperoxaluria (e.g., spinach, nuts), hypocitraturia.
  • Struvite (Magnesium Ammonium Phosphate, 10-15%): Staghorn calculi. Radiopaque. Coffin-lid crystals. Associated with urea-splitting bacteria (e.g., Proteus, Klebsiella). Urine pH > 7.2.
  • Uric Acid (5-10%): Radiolucent (usually). Rhomboid/rosette crystals. Risk: Gout, acidic urine (pH < 5.5), high purine diet, myeloproliferative disorders.
  • Cystine (1-2%): Radiolucent/faintly opaque. Hexagonal crystals. Autosomal recessive cystinuria. Positive nitroprusside test.

⭐ Calcium oxalate stones are the most common type of renal calculi (approx. 70-80%).

• General Risk Factors: Dehydration (↓ urine volume), infection, urinary stasis, metabolic disorders, family history, diet. 📌 Struvite, Staghorn, Sepsis (infection).

Urinary Tract Obstruction and Stones - Crystal Cases

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High‑Yield Points - ⚡ Biggest Takeaways

• Calcium oxalate stones: Most common; hypercalciuria is a key risk.
• Struvite stones: Linked to UTIs by urease-producers (Proteus); form staghorn calculi.
• Uric acid stones: Radiolucent; associated with gout, acidic urine.
• Cystine stones: Result from cystinuria (AR); show hexagonal crystals.
• Hydronephrosis: Consequence of obstruction; can lead to renal atrophy.
• Renal colic: Severe flank pain radiating to loin/groin; classic symptom.
• NCCT: Gold standard for diagnosing most urinary stones.