Urolithiasis

Question 1

Definition of urolithiasis

Answer 1

• formation of kidney stones/renal calculi within the urinary tract
• often begins in the calyces & pelvis, some develop in the lower urinary tract

Question 2

Causes of urolithiasis (2)

Answer 2

1. Primary
   - supersaturation of urine w crystalline material (most commonly calcium)
   - low urine volume
2. Secondary
   - UTI - crystalline material encrust on a necrotic focus on the mucosa
   - indwelling catheter/foreign body in bladder
   - vit A def - squamous metaplasia of upp urinary tract mucosa
   - low urinary pH - uric acid stones

Question 3

Types of renal calculi (4)

Answer 3

1. Calcium stones (65-70%)
2. Triple stones (15%)
3. Urate stones (6%)
4. Cystine stones (3%)

Question 4

Features of calcium stones

Answer 4

• composed of calcium oxalate +/- calcium phosphate
• most common cause = supersaturation 2 to hypercalciuria
• hypercalciuria may be idiopathic (55%) or with associated hypercalcemia due to hyperparathy, diffuse bone disease, vit D intoxication, milk-alkali syndrome, renal tubular acidosis of Cushing’s syndrome, sarcoidosis
• other causes: hyperoxaluria, increased uric acid secretion (hyperuricosuric calcium nephrolithiasis)

Question 5

Features of triple stones

Answer 5

• magnesium ammonium phosphate
• assoc w infections by urea splitting bacteria eg proteus - converts urea to ammonia - alkaline urine - promotes ppt of salts
• high urea content - huge stones - staghorn calculi

Question 6

Features of urate stones

Answer 6

• from uric acid

- predisposing factors: hyperuricemia (gout, leukemia), low urinary pH

Question 7

Features of cystine stones

Answer 7

• associated with genetic defects in renal transport/amino acids

Question 8

Effects of urolithiasis (3)

Answer 8

1. Urinary stasis - infection, further stone formation, obstruction
2. Ulceration - bleeding (hematuria), fistula formation
3. Pain, urinary colic