Urinary tract stones (urolithiasis) are solid mineral deposits that form in the kidney and may pass through the ureters, bladder, and urethra. They cause obstruction, infection, and renal dysfunction depending on their size, location, and composition.
I. Pathophysiology of Stone Formation
Stone formation occurs due to supersaturation of urine with lithogenic substances like calcium, oxalate, phosphate, uric acid, or cystine.
Key Pathways in Stone Formation:
- Supersaturation → Increased concentration of solutes (e.g., Ca2+, oxalate, uric acid)
- Nucleation → Formation of crystal nuclei
- Growth & Aggregation → Crystals aggregate into larger stones
- Retention in the Urinary Tract → Adherence to renal tubules or urothelium
- Obstruction & Symptoms Development
🔹 Predisposing Factors:
✔️ Dehydration (low urine output)
✔️ Hypercalciuria (high calcium excretion)
✔️ Hyperoxaluria (dietary oxalates, GI diseases)
✔️ Hyperuricosuria (high uric acid excretion)
✔️ Urinary stasis (BPH, vesicoureteral reflux)
✔️ Infection (Proteus, Klebsiella, Pseudomonas)
II. Types of Urinary Tract Stones & Composition
| Stone Type | Composition | Risk Factors | Imaging Findings | pH |
|---|---|---|---|---|
| Calcium Oxalate (75%) | Calcium & oxalate | Dehydration, Hypercalciuria, High oxalate diet | Radiopaque on X-ray & CT | Acidic to Neutral |
| Calcium Phosphate | Calcium & phosphate | Hyperparathyroidism, RTA Type 1 | Radiopaque on X-ray & CT | Alkaline |
| Uric Acid | Uric acid | Gout, High purine diet, Acidic urine | Radiolucent on X-ray, visible on CT | Acidic |
| Struvite (Infection stones) | Magnesium, Ammonium, Phosphate | UTI with urease-producing bacteria | Radiopaque, Large Staghorn calculi | Alkaline |
| Cystine | Cystine | Genetic defect (Cystinuria) | Faintly radiopaque on X-ray | Acidic |
III. Clinical Features Based on Location
| Stone Location | Signs & Symptoms | Key Findings |
|---|---|---|
| Kidney (Nephrolithiasis) | Flank pain, hematuria, dull ache, pyelonephritis if infected | Costovertebral angle (CVA) tenderness |
| Ureter (Ureterolithiasis) | Severe colicky flank pain radiating to groin, nausea/vomiting, hematuria | Ureteric colic, hydronephrosis on USG |
| Bladder (Cystolithiasis) | Dysuria, hematuria, frequency, urgency, suprapubic pain | Large stone on bladder ultrasound |
| Urethra (Urethrolithiasis) | Severe pain, difficulty urinating, urinary retention | Urethral obstruction, hematuria |
💡 Classical Ureteric Colic: Sudden onset, unilateral flank pain, radiating to groin/testis/labia, severe & intermittent.
IV. Diagnostic Investigations for Urinary Stones
1. Urinalysis (UA)
| Test | Findings in Stone Disease |
|---|---|
| Hematuria | + RBCs, microscopic or gross hematuria |
| pH Alteration | Acidic (Uric acid, Cystine), Alkaline (Struvite) |
| Crystals | Calcium oxalate, Uric acid, Struvite |
| Leukocytes & Nitrites | Suggestive of infection (UTI) |
2. Blood Tests
| Test | Purpose | Findings |
|---|---|---|
| Serum Creatinine & BUN | Assess kidney function | Elevated in obstructive uropathy |
| Calcium, Uric Acid, Phosphate | Identify metabolic causes | Hypercalcemia (Hyperparathyroidism), Hyperuricemia (Gout) |
3. Imaging Studies
| Modality | Findings | Sensitivity |
|---|---|---|
| X-ray KUB | Radiopaque stones (Calcium, Struvite) | 50-60% |
| Non-contrast CT (Gold Standard) | Detects all stones, location, hydronephrosis | 95-100% |
| Ultrasound (USG-KUB) | Hydronephrosis, stone size & obstruction | 85% |
| IV Pyelography (IVP) | Functional & structural evaluation | 85% |
🔹 Best Test? Non-contrast CT (fastest & most accurate).
🔹 Best for Pregnancy? Ultrasound (USG-KUB) (no radiation).
V. Differential Diagnosis of Urolithiasis
| Condition | Key Differentiating Features |
|---|---|
| Pyelonephritis | Fever, chills, CVA tenderness, WBC casts in urine |
| Renal Tumor (RCC) | Painless hematuria, mass on imaging |
| AAA (Aortic Aneurysm) | Pulsatile abdominal mass, hypotension |
| Biliary Colic | RUQ pain, no hematuria |
| Appendicitis | RLQ pain, rebound tenderness |
VI. Treatment Approach Based on Stone Size
| Stone Size | Management |
|---|---|
| <5 mm | Conservative: Hydration, Analgesia (NSAIDs), Tamsulosin |
| 5-10 mm | Medical Expulsive Therapy (Tamsulosin, Nifedipine) |
| >10 mm | Shock Wave Lithotripsy (ESWL), Ureteroscopy (URS), or Percutaneous Nephrolithotomy (PCNL) |
| Staghorn Calculi | Percutaneous Nephrolithotomy (PCNL), Antibiotics |
VII. Advanced Management Strategies
1. Conservative Management (Stones <5mm)
✔️ Hydration: 2.5-3L fluid/day
✔️ NSAIDs: Diclofenac, Ibuprofen (Pain relief)
✔️ Alpha-blockers: Tamsulosin (Facilitates passage)
✔️ Dietary Changes:
- Reduce Oxalate: Spinach, Nuts, Tea
- Reduce Sodium: High salt increases calcium excretion
- Increase Citrate Intake: Lemon juice, Citrus fruits
2. Surgical Management (Stones >10mm, Obstruction, Infection)
✔️ Extracorporeal Shock Wave Lithotripsy (ESWL) – Best for stones <2 cm
✔️ Ureteroscopy (URS) with Laser Lithotripsy – Best for mid-distal ureteric stones
✔️ Percutaneous Nephrolithotomy (PCNL) – Large renal stones (>2cm)
✔️ Open Surgery (Rare) – Only for complex cases
VIII. Prevention Strategies
🔹 For Calcium Stones:
✔️ Thiazide diuretics (↓ Calcium excretion)
✔️ Avoid excessive Vitamin D, dairy overuse
🔹 For Uric Acid Stones:
✔️ Allopurinol (↓ Uric acid levels)
✔️ Alkalinization of urine (Potassium citrate)
🔹 For Struvite Stones:
✔️ Antibiotics (Long-term UTI prophylaxis)
IX. Clinical Decision-Making Flowchart
📌 Step 1: Assess Symptoms → Colicky flank pain, hematuria
📌 Step 2: Order Urinalysis & Blood Tests
📌 Step 3: Imaging (USG for pregnancy, CT for best accuracy)
📌 Step 4: Management Based on Size & Symptoms
📌 Step 5: Prevent Recurrence (Diet, Hydration, Medication)
Final Thoughts
- Non-contrast CT is the gold standard for diagnosis
- Tamsulosin helps in stone passage for moderate-sized stones
- For stones >10mm, intervention (ESWL, URS, PCNL) is needed
- Dietary changes play a crucial role in prevention