Stone formation — kidney and gallbladder stones

1. Kidney Stones (Urolithiasis)

• Stone (calculus) formation anywhere in the urinary collecting system; all contain a mucoprotein organic matrix.
• General cause: urine supersaturation of the stone’s constituent beyond solubility + lack of inhibitors (e.g. citrate).

Stone types

Type	%	Key cause / pH
Calcium oxalate / phosphate	~80%	Hypercalcemia/hypercalciuria, hyperuricosuria; high pH; light brown
Struvite (Mg-ammonium-phosphate)	~10%	Urease+ infection (Proteus) → alkaline urine; large, dark; staghorn calculi
Uric acid	6–7%	Low pH, gout, leukemia; radiolucent
Cystine	1–2%	Genetic transporter defect; low pH

Morphology & Clinical

• 80% unilateral; renal pelvis/calyces/bladder; smooth or jagged; staghorn fills pelvis + calyces.
• Large pelvic stones may be silent; small stones → ureter → severe colicky pain radiating to groin + hematuria; obstruction → ulceration/bleeding. Diagnosed radiologically.

2. Gallbladder Stones (Cholelithiasis)

• Risk factors: age, female (2×), Western societies, genetics, ↓gallbladder motility (pregnancy, weight loss, spinal cord injury).
• 70–80% asymptomatic; symptomatic → biliary colic, cholecystitis, empyema/perforation/fistula, cholestasis, pancreatitis, intestinal obstruction.

Cholesterol stones

• Crystalline cholesterol monohydrate; 4 factors: bile cholesterol supersaturation, nucleation, gallbladder hypomotility/stasis, mucus hypersecretion.
• Risks: estrogen (↑hepatic cholesterol secretion), obesity/rapid weight loss, hyperlipidemia.
• Only in gallbladder; ovoid, firm; 80% radiolucent.

Pigment stones

• From unconjugated bilirubin (hemolysis, biliary infection) → insoluble calcium bilirubinate.
• Black = sterile bile, small, often radiopaque; brown = infected ducts, soft/greasy, radiolucent.

💡 High-yield: Calcium stones (commonest, radiopaque) — manage with thiazides/citrate; struvite → staghorn from urease+ infection; uric acid (radiolucent, acidic urine) — alkalinize + allopurinol. Gallstones: cholesterol (4F, radiolucent) vs pigment (hemolysis/infection).