Definition
Nephrolithiasis refers to the formation of solid calculi (stones) in the renal pelvis, calyces, ureter, or bladder, either unilaterally or bilaterally. These stones are formed due to supersaturation of urine with crystal-forming substances, leading to precipitation and aggregation into stones.
Etiology / Risk Factors
- Supersaturation of urine with substances such as calcium, oxalate, uric acid, or cystine.
- Dehydration (↓ urine volume = ↑ concentration of solutes).
- Dietary factors:
- High sodium → ↑ calcium excretion (calcium oxalate stones).
- High protein → ↑ uric acid and ↓ urine pH.
- Hypercalciuria (idiopathic or due to hyperparathyroidism).
- Hyperuricosuria → uric acid stones.
- Chronic UTIs by urease-producing organisms (e.g., Proteus, Klebsiella) → struvite stones.
- Genetic causes (e.g., cystinuria → cystine stones).
Pathogenesis
- 1. Supersaturation of urine with stone-forming substances.
- 2. Crystal nucleation and aggregation into a stone.
- 3. Stones often form in the renal pelvis and are initially painless.
- 4. Pain begins when a stone moves and obstructs the ureter:
- Ureteric obstruction → ↑ intraluminal pressure.
- Results in ureteral spasm, renal colic, hydronephrosis.
- 5. Ischemic injury may occur due to vasoconstriction and cytokine-mediated inflammation.