Writeva short note on urolithiasis
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Urolithiasis
Definition and Epidemiology
Urolithiasis refers to the formation of calculi (stones) anywhere in the urinary tract - kidneys, ureters, urinary bladder, or urethra. It is one of the oldest diseases known to mankind; the first documented cystolithotomy was described by Sushruta around 600 BCE. The lifetime prevalence varies from 1-20% across populations. Men are twice as likely to develop stones as women; in men the peak incidence is in the fourth to sixth decade, while women show a bimodal peak in the third decade and during the postmenopausal period. Recurrence is high, with 50% of patients having a recurrence within the first decade of diagnosis. - Bailey and Love's Short Practice of Surgery, 28th Ed.
Pathogenesis
Stone formation occurs when the concentration of stone-forming solutes (calcium, oxalate, uric acid) exceeds the ability of urine inhibitors to keep them in solution. Normal urinary inhibitors include citrate, magnesium, potassium, and Tamm-Horsfall mucoproteins. When these are overwhelmed, crystals precipitate and may anchor onto renal papillae to form Randall's plaques, which act as a nidus for stone growth.
Urine pH is a key modulator:
- Acidic urine (low pH) promotes uric acid stone formation
- Alkaline urine (high pH) promotes calcium phosphate and struvite stone formation
Urinary stasis also promotes stone formation, producing "milk of calcium stones" which are typically multiple, round, and smooth-surfaced. - Bailey and Love's Short Practice of Surgery, 28th Ed.
Types of Stones
| Stone Type | Frequency | Key Features |
|---|---|---|
| Calcium oxalate | 60-85% | Most common; associated with hypercalciuria, hyperoxaluria, hypocitraturia |
| Uric acid | ~10% | Radiolucent; form in acidic urine; associated with gout and myeloproliferative disorders |
| Struvite (infection) | ~10-15% | Form with urease-producing bacteria (Proteus, Klebsiella, Serratia); can grow into staghorn calculi |
| Calcium phosphate | Rare | Brushite (distal RTA); Apatite (infection) |
| Cystine | ~1% | Autosomal recessive cystinuria; very hard, resistant to SWL |
Staghorn calculi are branching struvite stones that fill the entire pelvicalyceal system. They cause significant morbidity through chronic infection and obstructive uropathy, and complete clearance is mandatory as residual fragments perpetuate bacteriuria and rapid recurrence.
Risk Factors
Non-modifiable: Age, male sex, White ethnicity, family history (risk 2.5x higher with positive family history), hereditary conditions (cystinuria, Type I renal tubular acidosis, primary hyperoxaluria).
Modifiable: Hot/arid climate (dehydration and increased perspiration), low fluid intake, high oxalate or purine diet, obesity, certain drugs (corticosteroids, chemotherapy, indinavir).
Clinical Features
- Renal colic: The classic presentation - sudden-onset, excruciating, colicky flank pain radiating to the groin, scrotum, or labia, caused by hyperperistalsis of ureteral muscle against an obstructing stone
- Haematuria: Gross or microscopic (present in the majority of episodes)
- Dysuria, urgency, frequency: Especially with lower ureteric or ureterovesical junction (UVJ) stones
- Nausea and vomiting
- Calculuria: Sand or gravel in the urine
- Fever and rigors: Indicates underlying UTI - a urological emergency
- Asymptomatic: Many stones are now detected incidentally on imaging
Diagnosis
- Urinalysis: Microscopic haematuria in most; pyuria with infection; urine pH; crystal identification
- Bloods: Serum calcium, phosphorus, uric acid; full blood count (leucocytosis suggests infection); renal function
- KUB X-ray: Good first-line test; detects radio-opaque stones (calcium oxalate and phosphate). Uric acid stones are radiolucent on plain X-ray.
- Ultrasound (US): Non-invasive; detects hydronephrosis; avoids radiation; useful in pregnancy
- Non-contrast CT (NCCT): The investigation of choice - sensitivity 96-100%, specificity 92-100%. Detects all stone types except indinavir stones. Soft-tissue rim sign (ureteral wall edema around the stone) helps differentiate a ureteric calculus from a pelvic phlebolith. - Campbell Walsh Wein Urology, 3-Volume Set
Low-dose NCCT protocols reduce radiation exposure by 50-75% while maintaining ~96% sensitivity and 97% specificity, and are appropriate for initial diagnosis and follow-up.
Management
Conservative (Watchful Waiting)
Stones <5 mm with no obstruction, no infection, and preserved renal function may be managed expectantly. Approximately 80% of stones <4 mm and around 60% of 4-10 mm stones pass spontaneously.
Medical Expulsive Therapy (MET)
- Tamsulosin (alpha-1 adrenergic blocker): Relaxes smooth muscle of the distal ureter, facilitating stone passage. Used for distal ureteric stones >5 mm.
- Analgesia: NSAIDs are first-line for renal colic; paracetamol is effective. Antispasmodics are not routinely indicated.
Extracorporeal Shock Wave Lithotripsy (SWL/ESWL)
Introduced in 1980 by Christian Chaussy. Focused acoustic pulse waves (located by fluoroscopy or US) are targeted at the stone, causing fragmentation through mechanical stress and cavitation bubble collapse. Used for:
- Ureteral calculi <10 mm (with ureteroscopy as alternative for >10 mm)
- Non-lower pole renal stones <20 mm
A known complication is Steinstrasse ("street of stones") - a row of stone fragments in the distal ureter that can cause obstruction and may need further intervention.
Endourological Procedures
- Ureteroscopy (URS): Rigid or flexible scopes used for ureteral and renal stones. Can use laser (holmium), pneumatic, or electrohydraulic energy. Preferred for ureteral stones >10 mm; stone-free rate higher than SWL.
- Retrograde Intrarenal Surgery (RIRS): Flexible ureteroscope with active tip deflection and laser; used for renal stones <2 cm, lower pole stones, in obese patients, and those with anatomic anomalies.
- Percutaneous Nephrolithotomy (PCNL): Creation of a percutaneous track into the pelvicalyceal system (usually prone, via the posterolateral calyx). Indicated for stones >20 mm, lower pole stones >10 mm, ESWL-refractory stones, and staghorn calculi. Complications include bleeding (may require angioembolisation), infection, and pleural injury with supracostal access.
Surgical Indications
- Failure of medical/conservative management
- Impaired renal function
- Chronic infection (staghorn calculi, matrix stones)
- High-risk occupation (pilots, drivers, sailors)
- Patient preference
Prevention and Metabolic Evaluation
High fluid intake (urine output >2 L/day) is the single most important preventive measure. Further evaluation targets the specific stone type:
- Calcium oxalate: Low oxalate diet, potassium citrate (raises urinary citrate and pH), thiazide diuretics (reduce hypercalciuria)
- Uric acid: Urinary alkalinisation with potassium citrate or sodium bicarbonate; allopurinol for hyperuricaemia
- Cystine: High fluid intake, urinary alkalinisation, D-penicillamine or tiopronin for refractory cases
- Struvite/Infection stones: Complete stone removal + long-term antimicrobial chemoprophylaxis
Complications
- Calculous anuria: Bilateral obstructing stones or stone in a solitary kidney
- Pyonephrosis / Renal abscess / Septicaemia
- Xanthogranulomatous pyelonephritis (XGP)
- Pyeloenteric or cutaneous fistulae (in neglected cases)
- Chronic renal failure: From recurrent obstruction and infection
Sources: Bailey and Love's Short Practice of Surgery, 28th Ed. | Campbell Walsh Wein Urology, 3-Volume Set | Brenner and Rector's The Kidney
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