Urinary: Renal Stones Flashcards
What is the most common site for stones to form?
The renal pelvis
however they can form anywhere in the urinary tract
What are the causes of bladder stones?
Bladder outflow obstruction eg urethral stricture, prostate obstruction, neuropathic bladder (cant contract properly)
- gives time for the crystals to form
Presence of a foreign body eg catheter
Most are passed down from upper urinary tract
Drugs
Idiopathic
Who do renal stones effect?
People aged over 30
2x more common in men (except struvite stones which are related to UTIs therefore more common in women)
What are renal stones made of?
Calcium stones: (99%)
- calcium oxalate with calcium phosphate
- calcium phosphate alone
- uric acid
- struvite - triple phosphate stones
Others: (1-2%)
- cysteine stones (occur in rare genetic disorder causing cystinuria)
- drug stones
- ammonium acid urate stones
Why do urinary stones form?
If the urine is supersaturated with minerals - means there is more solute than can be held in solution, so they form solid crystals.
How can the urine become supersaturated?
- Decrease in water content eg dehydration (people with stones advised to drink a lot of water)
- Increase in mineral content eg hypercalcaemia which is treatable
- Decrease in solubility of a solute in urine eg a change in pH
Hypercalciuria is a common abnormality in stone formers. What are the causes?
- idiopathic
- hypercalcaemia
- excessive dietary intake
- excessive resorption from skeleton eg prolonged immobilisation or weightlessness (astronauts)
What are the causes of hypercalcaemia?
Hypersecretion of PTH -> increase bone resorption:
- primary = hyperparathyroidism
- secondary to renal failure which usually causes retention of phosphate so hypocalcaemia
- ectopic secretion of PTH-related protein by malignant tumour eg squamous cell carcinoma of lung
Destruction of bone tissue by tumours, metastases, Pagets increased bone turnover, immobilisation
Others - excessive vit D, thiazide diuretics, sarcoidosis
What are the signs of hypercalcaemia?
BONES - pian and fractures
STONES
GROANS in abdo - constipation, ulcers, pancreatitis
MOANS - depression, lethargy, seizures
What are struvite stones?
They are ‘infection stones’ which form secondary to UTIs with organisms with the enzyme urease
Also the protduction of mucoprotein from infection provides a matrix for the stones to grow on.
They tend to form staghorn calculus - same shape as renal pelvis (they are very large)
When do uric acid stones form?
Form when there is hyperuricaemia (also causes gout) which is often see in dehydration and tumour lysis syndrome
Also seen in people which have urine with pH <5.5
You cannot see them on xray.
How do renal stones present?
Most are asymptomatic.
Can get renal colic - agonising, caused by spasm of ureter as it attempts to expel the stone Recurrent UTIs Haematuria Renal failure Urinary tract obstruction
What investigations are done when there is a suspected renal stone?
MSU - look for haematuria, urinary casts, culture
Serum - urea, creatinine, electrolytes, calcium
Abdo xray (uric acid stones cant be seen)
CT - can see all stone types
What complications can occur from renal stones?
Acute pyelonephritis +/- gram negative septicaemia
Pressure necrosis of renal parenchyma
Hydronephrosis from urinary obsruction
Ulceration through the wall of collecting system
How are urinary stones treated?
- Analgesia with rest and warmth to the site of pain
- Stones in the bladder or lower ureter can be grabbed in ureteroscopy
- Extracorporeal shock wave lithotripsy (fragments stones so that they can be passed more easily)
