Urolithiasis
- Can form at any level of the urinary tract
- Affects 5-10% of the population M>F. Age at onset between 20 to 30
- There is a hereditary disposition to forming stones; gout, cystinuria, primary hyperoxaluria
Causes and pathogenesis
- There are 4 main types of calculi;
- Most stones (70%) are calcium containing composed mostly of calcium oxalate or calcium oxalate mixed with calcium phosphate
- 15% are celled triple stones and are composed of magnesium ammonium phosphate
- 5-10% are uric acid stones
- 1-2% are made up of cystine
- Most stones (70%) are calcium containing composed mostly of calcium oxalate or calcium oxalate mixed with calcium phosphate
- Around 1-5% of the stone regardless of type is made up of mucoprotein
- Due to increased urinary concentration of the stones constituents such that supersaturation occurs. This may be favoured by a low urine volume
- Calcium oxalate stones are associated with hypercalcaemia in 5% of patients
- Magnesium ammonium phosphate stones are formed largely after infection with urea splitting bacteria such as proteus which split urea to ammonia
- The resulting alkali urine causes precipitation of magnesium ammonium phosphate stones
- These are some of the largest stones
- Uric acid stones are common in patients with hyperuricaemia such as gout of diseases with a high cell turnover such as leukaemia
- In the patients that develop these stones without hyperuricaemia it may be that their urine has a particularly acidic pH resulting in predisposition to stones
- As opposed to calcium containing stones these are radiolucent
- Cystine stones are caused by genetic defects in the renal reabsorption of amino acids including cystine, leading to cystinuria. Stones form at low pH
It has been suggested that stone formation is enhanced by a deficiency in inhibitors of crystal formation in urine. Such inhibitors include;
- Pyrophosphate
- Disphosphonate
- Citrate
- Glycosaminoglycans
- Osteopontin
- Glycoprotein called nephrocalcin
Morphology
- Unilateral in 80% of cases
- Favoured site is within the renal calyces and pelves and in the bladder
- They may be smooth or have rough contours
- Progressive accretion of salts leads to the development of branching structures known as staghorn stones which create a cast of the pelvic and calyceal system
Clinical course
- They may obstruct urinary flow or produce ulceration and bleeding
- Smaller stones are more hazardous as they can pass into the ureters and produce renal colic as well as ureteric obstruction
- Larger stones cant enter the ureters and are more likely to remain silent but may manifest as haematuria
- Stones predispose to infection both by their obstructive nature but also due to the trauma they cause