Urolithiasis in small animals Flashcards
Size - uroliths
macroscopic (crystals = microscopic)
T/F: you can have crystals without uroliths and uroliths without crystals
True
Are crystals always representative of urolith type?
May be but not always
How are uroliths described?
- mineral component
- location
How are uroliths formed?
- crystlas form when urine is supersaturated
- concentration of solute required to start the process (nucleation) generally higher than that needed for growth
PE - nephroliths and ureteroliths
- often normal
- hydronephrsis/ irregular kidneys
CS - cystoliths
- dysuria
- pollakiuria
- haematuria
- inappropriate urination
- generally not palpation
CS - urethroliths
- abdominal discomfort
- poor/no urine stream
- licking genitals
- obstruction and post-renal azotaemia
- enlarged painful bladder, urethroliths may be palpable per rectum or at base of penis
Dx - urolithiasis
- compatible hx and CS
- plain radiographs (radiodence uroliths if sufficienctly large)
- contrast radiograph (excretory urogram for nephroliths, reteroliths, double contrast - bladder, retrograde - urethra)
- ultrasound
How can you predict urolith type?
- signalment
- radiopaque/lucent
- urine pH
- hx of a particular stone type
- UTI associated with struvite
- disease associations
Urinalysis - analysis
- qualitative analysis not reliable
- quantitative analysis required (reputable lab) = xray diffraction (detailed analysis of mineral composition)
General tx considerations - renal and ureteral stone
- sx removal (traumatic)
- urinary bypass
- lithotripsy (non-UK)
- dietary dissolution (must be non-obstructed, often CaCO3 which isn’t amenable to dissolution)
- benign neglect
General tx considerations - bladder stone
- medical dissolution
- voiding urohydropulsion (VUH)
- sx (cystotomy)
General tx considerations - urethral stone
- retrograde flush into bladder
- sx (urethrotomy, urethrostomy)
Indications - medical management
- prior to sx if appropriate
- no obstruction
- no CI to dietary therapy
- urolith composition amenable to dissolution
- struvite, cystine an durate
Principles - medical management of uroliths
- decreased concentration in urine by increasing water intake
- decrease quantity of calculogenic cyrstalloids by diet r drugs
- increase solubility of slats by changing urine pH by diet
- tx predisposing cause
Outline urohydropulsion
- fill bladder with saline
- position so urethra vertical
- agitate
- allow stones to settle
- initiate voiding
- conitnue pressure to keep brisk urine flow
- 3 days ABs
Other names - struvite crystals
- magnesium ammonium phosphate
- triple phosphate
Outline struvite crystals
- many breeds
- most dogs have concurrent UTI
- most female
- urease producing bacteria (Staph, Proteus)
- cleave urea –> ammonium + bicarbonate
- alkaline urine pH
- sterile in cats
Struvite - tx
- treat UTI for 3-4 weeks after radiographic resolution
- reduce urinary Mg, ammonium, phosphate
- maintain pH
Struvite prevention
- hill’s and royal canin preventative diets
- long term preventative tx not recommended for dogs unless sterile stones
- monitor for UTI recurrence
- diets designed to prevent struvite recurrence may lead to calcium oxalate stone formation
Signalment - calcium oxalate
- increased incidence, esp cats (inappropriate acidifying diet to prevent struvite but promotes oxalate)
- terriers, poodles, schnauzers, burmese, himalayan, persian
- older animals
- upper urinary tract
Calcium oxalate - tx
- sx
- urohydropulsion
- medical dissolution not possible
- ignore
- 60% recurrence within 3 years
Prevention - calcium oxalate
- increase water intake (least controversial idea)
- sodium supplementation? (salt –> drinks more. induces diuresis)
- neutralising urine pH won’t have a big effect (calcium oxalate solubility not pH dependent, acidiying diets promote calcium excretion)
What is laser lithotripsy?
- guided by cystoscopy
- fragments removed by VUH
- BUT energy absorbed by water (effects only within 1-2mm fibre tip)
Outline ammonium urate stones
- 8% canine stones
- DALMATIONS: reduced conversion of uric acid to allantoin, defective transport of uric acid into hepatocytes andout of urine
- Hepatic dysfunction: PSS, increased excretion of ammonia and urea.
- bulldogs and others
Ammonium urate - tx
- tx underlying liver disease and PSS
- otherwise dissolution
- tx any UTI
- reduce purine, neutral to alkalinepH (Hills u/d)
- allopurinol (competitively inhibits xanthine oxidase, reducing uric acid this can result in xanthine stones if protein not restricted)
Describe cystine stones
- 3% canine stones (breeds)
- renal tubular defect resulting in excess urine cystine which is poorly soluble
- typically middle aged, despite being a congenital problem
- radiolucent
- medical dissolution effective but v expensive
- cystine excretion decreased by castration
Describe calcium phosphate stones
- associated with primary hyperPTH
- also mixed urolith
- inerlaistion of blood clot
Describe calcium carbonate stones
- commonest in horses and rabbits
- high {Ca2+] in ruine
Describe silica stones
- GSDs predisposed
- rare
- associated with poor diets
Sx management of urolithiasis - indications
- UT obstruction
- unknown or unpredictable urolith composition
- failed medical tx
- presence of other urinary tract abnormalities
- immature dogs (d/t specific dietary requirements)
- owner preference
- cost
Sx options
- open viscus and remove calculi (nephrotomy, pyelotomy, ureterotomy, cystotomy, urethrotomy)
- provide urine diversion (create an artificial opening, usually permanent)
General sx considerations
- stabilise hyperkalaemic and severely azotaemic animals pre-sx
- ensure # and location of calculi are known immediately before sx
- place indwelling urinary catheter (with extension set) and empty bladder
- check all calculi / fragments of calculi are removed at end of sx
- submit calculi for quantitative analysis
Method - cystotomy
- place urinary catheter connected to an extension set prior to sx
- caudal midline ventral celiotomy, care entering peritoneal lcavity
- locate bladder and empty if necessary, place stay suture - prolene, in apex
- pack of abdominal cavity
- ventral midline cystotomy and use further stay sutures to aid manipulaiton
- remove obvious calculi (forceps)
- save for quantitative analysis and culture
- flush urethra with sterile saline - non-sterile assistant to do until ALL calculi removed
- close bladder using syntehtic absorbable material e.g. poliglecaprone = monocryl, single or double layer, continuous or interrupted, appositional or inverting, try and avoid placing stay suture in bladder lumen
What are end of cystotomy considerations?
- are all calculi removed
- consider xray post-op
- generally indwelling catheter not used
- usual to keep on IVFT for 12-24 hours
- need to be allowed to urinate frequently
- analgesia
- medical management (dependent on calculus)
Risks/complications - cystotomy
- not removing all calculi -> CS recur
- dehiscence of bladder –> uroperitoneum
- blood clot –> outflow obstruction
- CS: cystitis
Radiographic density of calcium oxalate monohydrate (COM)/ dihydrate (COD)
moderately to markedly radiopaue
Surface characteristics - COM/COD
sharp projections, mulberry shaped or smooth round uroliths
- COD may be jackstone shaped
Urine pH - COM/COD
acidic to neutral
Crystalluria with COM/COD
- COM crystals (dumbbell or picket fence shapes)
- COD (square envelopes)
UTI with COM/COD
None or secondary UTI with common uropathogens
Breeds - COM/COD
- miniature schnauzer
- lhasa apso
- YT
- bichon firse
- pomeranian
- shih tzu
- birmese, himalayan, persian
Uroliths of COM/COD
often multiple small uroliths in bladder. multiple nephrolights is present.
- males > females (dogs and cats)
Radiographic density - struvite
mod to markedly radiopaque
- larger uroliths more radiopaque
Surface characteristics - struvite
SINGLE: smooth or speculated, may assume shape of bladder
MULTIPLE: smooth surfaces where uroliths contact each other, often pyramidial
Urine pH - struvite
alkaline
Crystalluria with struvite
struvite or ‘triple phosphate’ crystals (coffin lid appearance)
UTI with struvite
urease producing organisms (staph,proteus, mycoplasma).
- sterile struvite uroliths in cocker spaniels and cats
Breeds - struvite
- miniature schnauzer
- shih tzu
- bichon firse
- miniature poodle
- cocker spaniel
- lhasa apso
Uroliths > what size are likely to be struvite?
> 1cm
Describe urate/xanthine stoes
- radiolucent to faintly radioopaque
- multiple smooth uroliths
- acidic urine
- ammonium urate crystals (yellow-brown ‘thornapple or spherical’) or amoprhous urate crystals
- no UTI or secondary UTI with common uropathogens. Rarely urease producing organisms
- Dalmation, english bulldog,miniature schnauzer, shih tzu, YT
- PSS or other liver dysfunction
- yellow-green urolith colour,
- DOGS: Males> females
- CATS: equal b/w sexes
Describe cystine stones
- radiolucent to moderately radioopaque
- multiple smooth round uroliths in bladde/urethra
- nephroliths staghorn shape
- acidic urine
- cystine crystalluria always abnormal
- no UTI or seconday UTI with common uropathogens
- mastiff, australian cattle dog, english bulldog, SBT, newfoundland, dachshund
- positive urine-cyanide nitroprusside test
- metabolic screening of urine available
- DOGS: males»»females
Describe calcium phosphate crystals
- moderately to markedly radioopaque
- SURFACE: hydroxyapatite (multiple small uroliths with variable shape) or brushite (multiple smooth round or pyramidal uroliths)
- alkaline to neutralurine pH for hydroxyapaptite, acidic for brushite
- crystalluria: amorphous phosphates or calcium phosphate crystals (thin prisms)
- no UTI or secondary UTI with common uropathogens
- YT, miniature schnauzer, bichon friese, shih tzu, springer spaniel, pomeranian, miniature poodle, cocker spaniel
- hypercalcaemia predisposes this
Describe silica crystals
- moderately radioopaque
- classic jackstone appearance
- acidic to neutral urine pH
- no crystalluria
- no UTI or secondary UTI with common uropathogens
- GSD, OESH, labrador retriever
- males»_space; females
