Urolithiasis Flashcards
What are crystals?
Microscopic
- do not cause clinical signs
- can have crystals without stones and vice versa
- can have stones and crystals of different types (though usually the same)
Which type of crystal is common in cats?
Struvite (esp if left sitting or in fridge)
How are urolithis described?
Mineral component
Location
> Tx. Depends on these
How do urolithis form?
- urine super saturated
- concentration of solute required to start the process (nucleation) generally higher than that required for growth
- if concentration decreased sufficiently then crystals dissolve
Is Calcium oxalate commonly excreted in urine?
- all carnivores and omnivores excrete excessive calcium oxalate than can be dissolved in an equivalent volume of water
- needs other binders to ensure it dissolves (eg. citrate)
What is seen in history and PE with neophroliths and ureteroliths?
- asymptomatic
- pyelonephritis
- renal failure (if bilateral obstruction or infection)
- renal colic? Rarely picked up
> PE often Normal - hydro nephrosis/irregular kidneys
Hx and PE with cystoliths?
- dysuria, pollakiuria, haematuria
- inapropriate urination
- generally not palpable
Hx and PE with urethroliths?
- abdo discomfort
- poor/no urine stream
- licking genitals
- obstruction and post renal azoteamia
- enlarged painful bladder, urethroliths may be palpable per rectum/base of os penis
How can urolithis be diagnosed?
> plain film - if radiopaque stones > contrast - excretory urogram for nephroliths, urethroliths - double contrast for bladder - retrograde for urethral > ultrasound
How can urolith type be predicted?
- signalment
- radiopaque or lucent
- ph
- Hx of stone type (will not always be the same type)
- UTI with struvite
- disease association
How should uroliths be analysed?
- NOT CHEMICAL TEST AT USUAL LAB!
- food companies may do for free (Royal can in)
- need X-ray diffraction
General Tx options for renal and ureteral stones?
- surgical (difficult, treaumatic)
- urinary bypass
- lithotripsy(not available UK but owners may ask)
- dietary dissolution (if non obstructed, often calcium oxalate not available to dissolution)
- benign neglect if not infected or causing a blockage
General Tx options for bladder stones?
- medical dissolution
- voiding urohydropropulsion
- surgery (cystotomy)
General Tx options for urethral stones?
- retrograde flush into bladder
- surgery (urethrotomy, urethrostomy)
When is medical management indicated?
- no obstruction
- no contraindications to dietary therapy
- urolith composition amenable to dissolution (struvite, cystine, urate)
What is medical management of stones?
- v concentration of urine
- decrease quantity of calculigenic crystalloids by diet or drug tx
- increase solubility of salts by changing ph (diet)
- Tx predisposing cause
What is urohydropulsion? Contra indication?
- fill bladder with saline
- position so urethra vertical
- agitate
- allow stones to settle
- initiate voiding
- continue pressure to keep brisk urine flow
- 3d Abx
What is struvite associated with in dogs and cats?
- UTIs in dogs
- form I sterile urine in cats
When do struvite crystals form? What are struvite made of?
> magnesium ammonium phosphate/ triple phosphate
DOGS
- UTI with urease producing bacteria (staph, proteus) -> production of ammonia + bicarb from urea
- pH ^
- mostly female
CATS
- often sterile
Tx struvite?
> Tx UTI for 3-4w after radiographic resolution > reduce urinary Mg, ammonium, phosphate > maintain pH ^ water intake > monitor progress - rads (size/density/number) - urinalysis (pH 6-6.5, USG
How radio opaque are struvite stones?
- Radiopaque
- Big
- pyramidal shape
Prevention of struvite formation?
- Hills and royal canin available
- long term preventative tx, not recommended for dogs unless sterile stones present
- monoitor for recurrence of UTIs
- diets designed to prevent struvite recurrence may -> calcium oxalate stone formation and are not necessary
How has calcium oxalate incidence changed?
- increased incidence especially in cats
- thought d/t inappropriate use of acidifying diets to prevent struvite!
Predispositions for calcium oxalate?
> breed - terriers, poodles, shnauzer - burmese, himalayan, persian > more males than females > older > upper urinary tract common
Appearance of calcium oxalate?
- radiopaque
- spiky
Tx calcium oxalate?
- NOT medical!
- need surgery or urohydropulsion
- can ignore
Do calcium oxalate stones often recur?
60% recurrence within 3 years
Prevention of calcium oxalate stones?
- increase water intake (dogs will eat soup!)
- sodium supplementation
- neutral/marginal alkaline urine pH
> but solubility of calcium oxalate not pH dependent
> more acidifying diet promotes calcium excretion
What is laser lithiotripsy
- break up stone so can be removed by urohydropulsion
- guided by cystoscopy
- energy absorbed by water so only affects 1-2mm
Which dogs are predisposed to Ammonium urate stones?
> dalmations, bulldogs and other breeds - genetic test for at risk breeds > hepatic dysfunction - PSS - ^ excretion ammonia and urea
How common are Ammonium urate stones?
- 8% stones
Why are Dalmatians PDF urate stones?
Lack transporter of Uric acid into hepatocytes (not enzyme as commonly stated)
Tx ammonium urate?
- tx underlying liver dz or PSS
- in other cases, dissolution is possible
- Treat UTIs
- reduce purines, neutral -> alkali pH (Hills U/D good)
- Allopurinol competitively inhibits xanthine oxidase -> v uric acis
- this can result in xanthine stones if protein not restricted
Prevention of urate stones?
- feed low protein diet
- alkalinsing diet
What causes Cystine stones? How common are these? How can they be dx?
- 3% canine stones from UK (breed pdf)
- renal tubular defect -> excess cystine (poorly soluble)
- seen in middle aged dogs despite being CONGENITAL problem
- radioLUCENT so need ultrasound
- medical tx effective but too expensive
Why does cystine Tx often fail?
Will recur, medical tx prohibitively expensive, multiple surgeries needed so usually PTS
Newly discovered method of Tx for cystine?
Castration decreases cystine excretion
When are Calcium phosohate stones seen?
- 1* hyperparathyroidism
- as part of a mixed urolith
- d/t mineralization / a blood clot
When are Calcium carbonate stones seen?
- most common in rabbits and horses
- high [Ca] in urine
When are Silica stones seen?
- GSD pdf
- associated with poor diet
- rare
Indications for surgery in smallies?
- obstruction
- Unknown or unpredictable urolith composition
- failure medical Tx
- presence of other UT abnormalities
- immature dogs
- owner preference
- cost
2 main surgical options?
> open viscus and removing -otomy - nephro - pyelo - uretero - cysto - urethro > provide urine diversion - -ostomy - usually permenant - urethrostomy > minimally invasive - specialist places only
What needs to be done prior to surgery?
- stabilise hyperkalaemia and severe azotaemia
- ensure number and location of calculi known immediately before surfery
- place in dwelling urinary catheter (extension set) and empty bladder
What must be done at end of surgery?
- check all calculi / fragments removed
- submit calculi for quantitative analysis
What are Halsteads principles of surgery
- gentle tissue handling
- accurate heamostasis
- preservation of adequate blood supply
- aseptic technique
- no tension on tissues
- careful tissue approximation
- obliteration of dead space
Outline cystotmy procedure
- catheter pre-surgical
- caudal midline ventral celiotomy, care entering peritoneal cavity
- locate bladder and empty if necessary
- stay suture (prolene) in Apex
- pack off abdominal cavity
- ventral midline cystotomy
- further stay sutures
- lots of blood! Need suction or cautery
- remove obvious calculi
- flush urethra with sterile saline(non sterile assistant) until all calculi removed
- close bladder with synthetic absorbable (eg. Poliglecaprone 25 MONOCRYL) doesn’t need to last long, heals quickly
- single or double layer
- appositional or inverting (never everting)
- try and avoid suture material in lumen of bladder
Post op care following cystotomy?
- Indwelling Catheter not used
- IVFT 12-24hours to prevent clot from Haematuria (can obstruct!)
- allow to urinate frequently
- analgesia
- medical, management depending on stone type
Commonest risks/complications with cystotomy?
- not removing all calculi
- dehiscence -> urileritoneum
- blood clot
- cystitis
What are urolithis? Other names?
Calculi, stones, urolithis - macroscopic
