Renal Calculi

Renal calculi: (urolithiasis or kidney stones) can arise at any level in the urinary tract; there are four types of calculi:

1. Calcium containing stones (75%), composed of calcium oxalate or calcium oxalate mixed with calcium phosphate

2. Triple stones or struvite stones (15%), composed of magnesium ammonium phosphate

3. Uric acid stones (6%)

4. Cystine stones (1-2%)

An organic matrix of mucoprotein, making up 1-5% of the stone weight is present in all calculi.

Pathogenesis:

Calcium-containing stones are usually associated with

• Hypercalcemia and hypercalciuria (60%) and

• Hyperoxaluria and hyperuricosuria (in others)

In about 25%, there is no demonstrable metabolic abnormality.

Struvite stones are associated with infection by urea-splitting bacteria that convert urea to ammonia. So-called staghorn calculi are almost always associated with infection.

Uric acid stones may (or may not) form in the presence of hyperuricemia or hyperuricosuria.

Increased concentrations of stone constituents, changes in urinary pH, decreased urine volume and bacteria all play a role in stone formation; but many calculi occur in the absence of these factors. Thus loss of inhibitors of crystal formation is postulated to play a role in the pathogenesis of some stones. These include citrate, pyrophosphate, glycosaminoglycans, and glycoproteins (nephrocalcin).

Complications:

Clinical symptoms frequently caused by renal calculi include:

• Obstruction,

• Ulceration,

• Bleeding

• Pain (known as renal colic)

Renal calculi also predisposes to renal infection.

Category: Pathology Notes