Urolithiasis Flashcards
What are the common crystal types normally found in the urine?
Calcium oxalate, struvite, amorphous phosphate
What are the abnormal crystal types found in the urine?
Urate, xanthine, cysteine
What is the significance of crystalluria?
Suggests urine is supersaturated with that compound
Struvite and oxalate form on storage
Describe the composition of a urolith
Central nidus around which the crystal forms.
Mixed urolith - contains
What can act as a nidus?
Infected bladder epithelium, suture material, crystals of a different type
Describe the aetiology of struvite crystals in dogs
associated with urease producing bacterial infections e.g. E. coli, Klebsiella, Staph, Mycoplasma
urease breaks down urea to ammonia and bicarbonate
ammonia binds to phosphate and magnesium and damages the GAG layer of the bladder wall
bicarbonate increases urine pH, reduces the solubility of struvite and increases the solubility of phosphate
Describe the aetiology of calcium oxalate crystals
males > females
predominant stone type in the kidney
can’t be dissolved, require surgical removal
urine becomes supersaturated with calcium and oxalate = reduction in concentration of inhibitory factors which prevent crystal/stone formation e.g. nephrocalcin citrate, pyrophosphate, magnesium
risk factors = hypercalcaemia, CKD
Describe the aetiology of purine stones
Group of uroliths - uric acid, urate salts, xanthine
Normally - uric acid is converted to allantoin in the liver which is then excreted in the urine (v soluble)
Abnormally - uric acid is not converted to allantoin and is excreted unchanged in the urine. Lower solubility, more likely to form stones.
Ammonium urate is the most common.
Dalmations, English bulldogs have an autosomal recessive gene which predisposes them to hyperuricaciduria and crystal/stone formation. (Prevents transport of uric acid into hepatocytes and resorption of uric acid in renal tubular cells)
How can uroliths present?
uretholith - LUT inflammation or obstruction
urocystolith - LUT inflammation, recurrent UTI, haematuria, asymptomatic
ureterolith - recurrent UTI, azotaemia/uraemia, asymptomatic
nephrolith - haematuria, azotaemia/uraemia, abdominal pain, non-specific signs, recurrent UTI
How are uroliths diagnosed?
Radiography
May need contrast as some stones are radiolucent
US isn’t as good as the stones cause acoustic shadowing, cannot count
How might uroliths contribute to bladder infection/UTI?
Movement of stones within bladder can cause damage to the bladder wall, allowing bacteria to colonise.
Prevent complete bladder emptying.
Stones can become a nidus of infection, allowing for recurrent UTIs.
What are the advantages to using radiography to diagnose?
Can image the whole UT.
Can assess size and number of stones present.
Can image the urethra.
