Urolithiasis - Comprehensive Review

1. PATHOLOGY

Definition

Epidemiology

• Lifetime prevalence varies from 1-20%; rising steadily over four decades in Western populations.
• By age 70, approximately 11% of men and 5.6% of women in the United States will have developed a symptomatic kidney stone.
• Recurrence is high: ~50% within the first decade of diagnosis.
• Men are twice as likely to form stones; peak incidence in the 4th-6th decades. Women show a bimodal peak (3rd decade and postmenopause).
• White individuals are at higher risk than other ethnic groups.
• Strong family history: patients with a positive family history are 2.5x more likely to develop stone disease.
• Robbins & Kumar Basic Pathology, p. 527; Bailey & Love's Surgery 28th ed., p. 1496

Pathogenesis

1. Supersaturation - When urinary concentration of lithogenic solutes (calcium, oxalate, uric acid, cystine) exceeds their solubility, crystallization is favored.
2. Inhibitor failure - Normal urine contains inhibitors of crystal growth: citrate, potassium, magnesium, Tamm-Horsfall mucoprotein. When these are depleted or overwhelmed, nucleation proceeds.
3. Crystal nucleation and growth - Crystals either pass with urine flow or anchor onto renal papillae forming Randall's plaques - subepithelial calcium phosphate deposits at the papillary tips that serve as a nidus.
4. pH effects - Acidic urine (pH <5.5) favors uric acid and cystine stone precipitation. Alkaline urine favors calcium phosphate and struvite stone formation.
5. Stasis - Urinary stasis promotes crystal aggregation, producing multiple round "milk of calcium" stones.
6. Organic matrix - All stone types contain ~2.5% organic mucoprotein matrix by weight.

• Bailey & Love's Surgery 28th ed., p. 1496; Robbins & Kumar Basic Pathology, p. 527

Stone Types

Nephrolithiasis: small golden-yellow calculi impacted in the renal pelvis (Robbins & Kumar Basic Pathology)

• Robbins & Kumar Basic Pathology, Table 12.5, p. 527-528; Bailey & Love's Surgery, p. 1496-1497

Calcium Stones - Causes in Detail

• Absorptive hypercalciuria: excessive intestinal calcium absorption - most common mechanism
• Renal hypercalciuria: primary tubular reabsorption defect
• Primary hyperparathyroidism: most common hypercalcemic cause - PTH increases bone resorption and activates 1,25-dihydroxyvitamin D3, driving intestinal calcium absorption
• Hyperoxaluria: enteric (after small bowel disease/resection - increased colonic oxalate absorption) or primary (rare enzyme defect)
• Hypocitraturia: citrate normally chelates calcium in urine, inhibiting crystallization; distal RTA is a key cause
• Hyperuricosuria: uric acid crystals act as nidi for calcium oxalate aggregation

Struvite Stones

• Exclusively occur with urease-producing bacteria (Proteus, Klebsiella, Serratia, Enterobacter)
• Urease hydrolyzes urea to CO2 and ammonium, alkalinizing urine
• Staghorn calculi fill and branch through the entire pelvicalyceal system
• Can grow to massive size before detection; cause chronic infection, obstructive uropathy, and renal failure
• Complete clearance is mandatory - residual fragments cause rapid recurrence

Uric Acid Stones

• 50% of uric acid stone formers have neither hyperuricemia nor increased urine urate - they simply excrete persistently acidic urine (pH <5.5)
• Radiolucent on plain radiograph; visible on CT
• Regional variation: highest prevalence in Middle East and some European countries

Cystine Stones

• Autosomal recessive defect in renal and intestinal amino acid transport (cystine, ornithine, lysine, arginine - COLA)
• Insoluble at physiologic pH; worsens with acidic urine
• Extremely hard due to disulfide bonds; resistant to ESWL

Morphology

• Unilateral in ~80% of patients
• Common sites: renal pelvis, calyces, bladder
• Average size: 2-3 mm; may be smooth or jagged
• Staghorn calculi: progressive accretion forms branching cast of the pelvicalyceal system; almost always struvite
• Stones cause mucosal ulceration and hemorrhage; obstruction leads to hydronephrosis
• Robbins & Kumar Basic Pathology, p. 528

2. MEDICINE (Clinical Assessment & Medical Management)

Clinical Presentation

• Asymptomatic: increasingly diagnosed incidentally on imaging (ultrasound, CT) - particularly large pelvic stones
• Ureteric colic (most common acute presentation): sudden-onset, excruciating, colicky flank pain radiating to the groin, scrotum/labia or inner thigh; caused by hyperperistalsis of ureteric musculature against the obstructing stone
  • Small 3-5 mm calculi lodge most commonly at the ureterovesical junction (UVJ)
  • Lower ureteric/UVJ stones cause urgency, frequency, dysuria
• Hematuria: gross or microscopic, present in most cases during colic
• Calculuria: passing of sand or gravel
• Nausea/vomiting: due to shared celiac innervation
• Fever + rigors: suggests concurrent UTI/urosepsis - a surgical emergency
• Malaise, weight loss: in longstanding infection stones or renal failure
• Bailey & Love's Surgery 28th ed., p. 1497; Robbins & Kumar Basic Pathology, p. 528

Differential Diagnosis of Ureteric Colic

• Urinary: clot colic (anticoagulation, haemophilia), papillary necrosis (diabetes, NSAIDs, sickle cell disease)
• Surgical: acute appendicitis, bowel obstruction, AAA
• Gynaecologic: ectopic pregnancy, ovarian torsion
• Malingering (opioid-seeking behaviour)

Investigations

• Urinalysis: hematuria (present in majority); pyuria (sterile or infected); urine pH
• Urine culture: if infection suspected or planned intervention
• Bloods: FBC (leukocytosis suggests infection), serum creatinine, electrolytes, serum calcium, uric acid, phosphorus; pregnancy test in women
• Plain KUB radiograph: detects radiopaque stones (calcium, struvite); misses uric acid and cystine stones
• Ultrasound: detects stones in kidney and UVJ; preferred first-line in children and pregnant women (avoids radiation)
• Non-contrast CT (NCCT): gold standard - detects virtually all stone types except indinavir; determines stone size, location, and degree of obstruction

• 24-hour urine: calcium, oxalate, uric acid, citrate, sodium, creatinine, phosphate, volume
• Serum: PTH (if hypercalcemic), uric acid
• Stone analysis: ideally analyze all passed or retrieved stones
• Risk stratification into low-risk (single stone, no metabolic abnormality) vs. high-risk formers

Medical Management

• Analgesia: NSAIDs (first-line; e.g., diclofenac) + paracetamol; antispasmodics are not necessary
• Opioids: for refractory pain
• IV hydration: if unable to tolerate orally or signs of sepsis
• Antibiotics: broad-spectrum empirical coverage if sepsis suspected; cultures before starting

• Alpha-blockers (tamsulosin): causes smooth muscle relaxation of distal ureteric wall; used for distal ureteric stones >5 mm and post-ESWL fragment passage
• Calcium channel blockers: also reduce dysmotive ureteric contractions
• Spontaneous passage rates: nearly all stones <4 mm pass; ~50% of 5-10 mm stones pass; >10 mm stones rarely pass spontaneously

• Fluid intake >2.5 litres/day (target urine output >2 L/day)
• Dietary calcium should NOT be restricted (paradoxically increases oxalate absorption); supplemental calcium at mealtimes
• Reduce animal protein and salt intake
• Reduce oxalate-rich foods (spinach, nuts, chocolate) in hyperoxaluric patients
• Bailey & Love's Surgery 28th ed., p. 1498-1499; Brenner & Rector's The Kidney, p. 1319

3. SURGERY

Indications for Intervention

• Failure of conservative/medical management
• Impaired or deteriorating renal function
• Complete ureteric obstruction
• Chronic/recurrent infection (staghorn calculi, matrix calculi)
• Urosepsis with obstruction (emergency decompression)
• High-risk occupation (pilots, sailors, long-distance drivers) or remote geographical location
• Patient preference
• Bailey & Love's Surgery 28th ed., p. 1498

Emergency Urinary Decompression

• Ureteric stenting (JJ/double-J stent): retrograde approach; provides internal drainage
• Percutaneous nephrostomy (PCN): antegrade approach; preferred when retrograde approach fails or is not feasible
• Stone removal (e.g., ureteroscopy) can be attempted in select stable patients without infection

Extracorporeal Shock Wave Lithotripsy (ESWL)

• Non-invasive; introduced by Christian Chaussy in 1980
• Mechanism: acoustic pulse waves focused on the stone (localized by fluoroscopy and/or ultrasound); stone fragments by direct mechanical stress from the shock wave and indirect cavitation (bubble collapse)
• Indications: renal and ureteric stones <2 cm; first-line for most renal stones <2 cm (unless lower-pole anatomy unfavorable)
• Contraindications: pregnancy, uncorrected bleeding diathesis, aortic/renal artery aneurysm, morbid obesity (depth to stone >10 cm), pacemaker (relative), distal obstruction, acute UTI
• Complication - Steinstrasse ("street of stones"): row of stone fragments lining the distal ureter after ESWL, particularly with high stone burden; usually pass spontaneously but may obstruct
• "Clinically insignificant residual fragments" (CIRFs) = ≤4 mm post-treatment; still 20-40% fail to clear and form a nidus

Ureteroscopy (URS) / Retrograde Intrarenal Surgery (RIRS)

• Rigid URS: for ureteric stones (proximal ureter to UVJ)
• Flexible URS / RIRS: for intrarenal stones; allows access to all calyces
• Energy sources: holmium:YAG laser (gold standard - most efficient; works on all stone types); also pneumatic, electrohydraulic, ultrasonic
• Indications: ureteric stones at any level; renal stones <2 cm; failed ESWL
• Avoided in children <5 years due to ureteric caliber
• Can be done as day-case procedure; does not require a skin incision

Percutaneous Nephrolithotomy (PCNL)

• Stone removal via a dilated percutaneous track (standard: >28 Fr) between skin and pelvicalyceal system
• Typically performed in prone position; posterolateral calyx is the usual entry point
• Localization: fluoroscopy or ultrasound guidance
• Energy sources: ultrasound in combination with pneumatic and laser lithotripsy

• Renal stones >2 cm
• Lower-pole renal stones with unfavorable anatomy for ESWL
• Failed ESWL or RIRS for renal calculi
• Staghorn calculi (complete clearance is mandatory)

• Pregnancy, untreated UTI, bleeding diathesis, current anticoagulation

• Bleeding (may require selective angioembolization for severe hemorrhage)
• Infection/sepsis
• Pleural violation (supracostal puncture - pneumothorax, hydrothorax)
• Perforation of adjacent organs

Open/Laparoscopic Surgery

• Reserved for complex, infected stones with anatomical abnormalities (e.g. horseshoe kidney, pelvic kidney, kyphoscoliosis) where endourological access is impossible
• Procedures: pyelolithotomy (stones in renal pelvis), anatrophic nephrolithotomy (complex intrarenal staghorn)
• Rarely performed in modern practice

Special Situation: Pregnancy

• Renal colic is the most common cause of non-obstetric hospital admission in pregnancy
• Physiological changes: increased GFR, ureteric dilation from progesterone and uterine compression
• Imaging: ultrasound first-line; MRI (no radiation); avoid CT if possible
• Management: conservative (most stones pass spontaneously); ureteric stent or PCN if obstruction; ESWL is contraindicated; URS can be performed if necessary
• Bailey & Love's Surgery 28th ed., p. 1498-1500

Summary Table

• Robbins & Kumar Basic Pathology, 10th ed. (Table 12.5, p. 527-528)
• Robbins, Cotran & Kumar Pathologic Basis of Disease, 10th ed.
• Bailey & Love's Short Practice of Surgery, 28th ed. (Chapter 82, p. 1496-1500)
• Brenner & Rector's The Kidney, 2-Vol Set (Chapter 38, p. 1277-1319)
• Campbell-Walsh-Wein Urology---

Urolithiasis - Comprehensive Review

1. PATHOLOGY

Definition

Epidemiology

• Lifetime prevalence: 1-20%; rising steadily over four decades in Western populations
• By age 70: ~11% of men and 5.6% of women in the US will develop a symptomatic kidney stone
• Recurrence is high: ~50% within the first decade
• Men are 2x more likely to form stones; peak incidence in the 4th-6th decades; women have a bimodal peak (3rd decade and postmenopause)
• White individuals have higher risk; family history confers 2.5x risk
• Estimated economic burden in the United States approaching $4.7 billion by 2030
• Robbins & Kumar Basic Pathology, p. 527; Bailey & Love's Surgery 28th ed., p. 1496; Brenner & Rector's The Kidney, p. 1277

Pathogenesis

1. Supersaturation - When urinary concentrations of lithogenic solutes exceed their solubility product, crystallization begins
2. Inhibitor failure - Normal urine contains crystal-growth inhibitors: citrate, potassium, magnesium, Tamm-Horsfall mucoprotein. When these are depleted or overwhelmed, nucleation proceeds
3. Crystal nucleation and anchoring - Crystals either pass with urine or anchor onto renal papillae as Randall's plaques (subepithelial calcium phosphate deposits), which serve as a fixed nidus
4. pH effects - Acidic urine (pH <5.5) favors uric acid and cystine precipitation; alkaline urine favors calcium phosphate and struvite formation
5. Urinary stasis - Promotes crystal aggregation; stasis stones are typically multiple, round, smooth ("milk of calcium stones")
6. Organic matrix - All stone types contain ~2.5% mucoprotein matrix by weight

• Bailey & Love's Surgery 28th ed., p. 1496; Robbins & Kumar Basic Pathology, p. 527

Stone Types

• Robbins & Kumar Basic Pathology, Table 12.5, p. 527-528

Calcium Stones - Causes

• Idiopathic hypercalciuria (50% of calcium stone formers): subdivided into absorptive (excessive gut calcium absorption) and renal (tubular reabsorption defect)
• Primary hyperparathyroidism: most common hypercalcemic cause; PTH drives bone resorption and 1,25-dihydroxyvitamin D3 synthesis, increasing intestinal calcium absorption
• Hyperoxaluria: enteric (ileal disease/resection increases colonic oxalate absorption) or primary (rare enzymatic defect)
• Hypocitraturia: distal RTA is the classic cause; citrate normally chelates urinary calcium
• Hyperuricosuria: uric acid crystals act as heterogeneous nidi for calcium oxalate crystallization
• No identified metabolic abnormality in 15-20% of calcium stone formers

Struvite Stones

• Form only in the presence of urease-producing bacteria: Proteus, Klebsiella, Serratia, Enterobacter
• Urease hydrolyzes urea to CO2 and ammonium, raising urine pH and precipitating magnesium-ammonium-phosphate
• Staghorn calculi - branch through the entire pelvicalyceal system; cause progressive renal destruction through chronic infection and obstructive uropathy; complete clearance is mandatory since residual fragments cause rapid recurrence and persistent bacteriuria

Uric Acid Stones

• Radiolucent on plain radiograph (but visible on CT - important diagnostic point)
• 50% of uric acid stone formers have neither hyperuricemia nor increased urinary urate; they simply excrete persistently acidic urine (pH <5.5) - unexplained
• Conditions causing hyperuricosuria: gout, myeloproliferative disorders post-cytotoxic therapy
• Highest geographic prevalence in the Middle East

Cystine Stones

• Autosomal recessive defect in renal proximal tubular and intestinal transport of cystine, ornithine, lysine, arginine (COLA)
• Cystine insoluble even at physiologic pH; worsens with acidic urine
• Very hard due to disulfide bonds - essentially resistant to ESWL

Morphology

• Unilateral in ~80% of patients
• Most common sites: renal pelvis, calyces, bladder
• Typically 2-3 mm; may be smooth or jagged
• Staghorn calculi: massive branching structures creating a cast of the pelvicalyceal system - almost always struvite
• Stones cause mucosal ulceration, hemorrhage, and obstruction; the latter leads to hydronephrosis and, if chronic, loss of renal function
• Robbins & Kumar Basic Pathology, p. 528

2. MEDICINE

Clinical Presentation

• Asymptomatic: increasingly diagnosed incidentally on imaging, especially large pelvic stones
• Ureteric colic: sudden-onset excruciating flank pain radiating to groin, scrotum/labia; caused by hyperperistalsis of ureteric musculature against an obstructing stone
  • Small (3-5 mm) calculi most commonly lodge at the ureterovesical junction (UVJ)
  • Lower ureteric/UVJ stones cause additional urgency, frequency, dysuria
• Hematuria: gross or microscopic in most cases
• Calculuria: passage of sand or gravel
• Nausea and vomiting: from shared celiac innervation
• Fever and rigors: indicates concurrent UTI/urosepsis - a urological emergency
• Malaise and weight loss: with longstanding infection stones or renal failure

Differential Diagnosis of Ureteric Colic

• Clot colic (anticoagulation, haemophilia), papillary necrosis
• Acute appendicitis, bowel obstruction, abdominal aortic aneurysm
• Ectopic pregnancy, ovarian torsion
• Malingering

Investigations

• Urinalysis: hematuria, pyuria (sterile or infected), pH
• Urine culture: if infection suspected or intervention planned
• Bloods: FBC, serum creatinine, electrolytes, calcium, uric acid; pregnancy test (women)
• Plain KUB: detects radiopaque stones; misses uric acid and most cystine stones
• Ultrasound: first-line in children, pregnant women; detects hydronephrosis and stones at kidney/UVJ
• Non-contrast CT (NCCT): gold standard - detects all stone types except indinavir; best for size, location, and degree of obstruction

• 24-hour urine: calcium, oxalate, uric acid, citrate, sodium, creatinine, volume
• Serum: PTH (if hypercalcemic), uric acid
• Stone analysis: analyze all passed or retrieved stones
• Stratify into low-risk (single stone, no metabolic abnormality) vs. high-risk formers

Medical Management

• NSAIDs (diclofenac, ketorolac) - first-line analgesic; antispasmodics are not necessary
• Opioids for refractory pain
• IV hydration if unable to tolerate orally or sepsis is present

• Alpha-1 blockers (tamsulosin): relaxes smooth muscle of the distal ureter; used for distal ureteric stones >5 mm and post-ESWL fragment passage
• Calcium channel blockers: also reduce dysmotive ureteric contractions while preserving expulsive peristalsis
• Spontaneous passage rates: ~95-100% for stones <4 mm; ~50% for 5-10 mm; rarely for >10 mm

• Fluid intake >2.5 L/day (target urine output >2 L/day)
• Do NOT restrict dietary calcium (paradoxically increases oxalate absorption - intestinal calcium binds oxalate in the gut and prevents its absorption)
• Supplemental calcium should be taken at mealtimes
• Reduce animal protein and sodium intake
• Bailey & Love's Surgery 28th ed., p. 1498-1499; Brenner & Rector's The Kidney, p. 1319

3. SURGERY

Indications for Surgical Intervention

• Failure of medical/conservative management
• Impaired or deteriorating renal function
• Complete ureteric obstruction
• Chronic or recurrent infection (staghorn calculi, matrix calculi)
• Urosepsis with obstruction (emergency)
• High-risk occupation (pilots, sailors, long-distance locomotive drivers) or remote geographical location
• Patient preference

Emergency Urinary Decompression

• JJ ureteric stent (retrograde; cystoscopy-guided): provides internal drainage
• Percutaneous nephrostomy (PCN) (antegrade): for failed retrograde approach or anatomical difficulty
• In selected stable patients without sepsis, ureteroscopy with stone removal can be performed primarily

Extracorporeal Shock Wave Lithotripsy (ESWL)

• Non-invasive, outpatient procedure; introduced by Christian Chaussy (1980)
• Mechanism: focused acoustic pulse waves (localized by fluoroscopy ± ultrasound) cause stone fragmentation through direct mechanical stress and cavitation (bubble collapse)
• Indications: renal and ureteric stones <2 cm; first-line for most renal stones <2 cm with favorable anatomy
• Absolute contraindications: pregnancy, uncorrected coagulopathy, active UTI, distal obstruction, aortic/renal artery aneurysm
• Relative contraindications: pacemaker, morbid obesity, musculoskeletal deformities, renal anomalies (horseshoe kidney, pelvic kidney)
• Complications:
  • Steinstrasse ("street of stones"): row of stone fragments lining the distal ureter; usually pass spontaneously but may obstruct
  • "Clinically insignificant residual fragments" (CIRFs, ≤4 mm): 20-40% fail to clear and form a nidus for recurrence

Ureteroscopy (URS) / Retrograde Intrarenal Surgery (RIRS)

• Rigid URS: ureteric stones from proximal ureter to UVJ
• Flexible URS / RIRS: intrarenal stones; access to all calyces
• Energy sources: holmium:YAG laser (gold standard - works on all stone compositions); pneumatic, electrohydraulic, ultrasonic also used
• Indications: ureteric stones at any level; renal stones <2 cm; failed ESWL
• Avoided in children <5 years due to ureteric caliber
• Day-case procedure; no skin incision required

Percutaneous Nephrolithotomy (PCNL)

• Removal of renal stones via a dilated percutaneous track (standard >28 Fr) between skin and pelvicalyceal system
• Position: typically prone; posterolateral calyx used as entry point
• Guidance: fluoroscopy or ultrasound
• Energy sources: ultrasound + pneumatic ± laser

• Renal stones >2 cm
• Lower-pole renal stones with anatomy unfavorable for ESWL
• Failed ESWL or RIRS
• Staghorn calculi (first-line; complete clearance mandatory)

• Hemorrhage (can require selective angioembolization)
• Sepsis/infection
• Pleural violation (supracostal puncture): pneumothorax, hydrothorax
• Injury to adjacent organs (bowel, spleen, liver)

Open/Laparoscopic Surgery

• Reserved for complex/infected stones with anatomical abnormalities preventing endourological access
• Procedures: pyelolithotomy (pelvic stones), anatrophic nephrolithotomy (complex staghorn)
• Rarely performed in the modern era

Special Situation: Pregnancy

• Renal colic = the most common cause of non-obstetric hospital admission in pregnancy
• Physiological changes: increased GFR, progesterone-mediated ureteric dilation, uterine compression
• Imaging: ultrasound first-line; MRI if needed; CT avoided where possible
• Treatment: conservative (most stones pass spontaneously); ureteric stent or PCN for obstruction; ESWL contraindicated; URS can be done if necessary
• Bailey & Love's Surgery 28th ed., p. 1499-1500

Quick Reference Summary

• Robbins & Kumar Basic Pathology, 10th ed., Table 12.5, p. 527-528
• Robbins, Cotran & Kumar Pathologic Basis of Disease, 10th ed.
• Bailey & Love's Short Practice of Surgery, 28th ed., Chapter 82, p. 1496-1500
• Brenner & Rector's The Kidney, 2-Vol Set, Chapter 38, p. 1277-1319
• Campbell-Walsh-Wein Urology, 12th ed.