Nephrolith management in Cats and Dogs
When NOT to ignore?
- Radiographs: size, number and clues about the type of nephrolith present
- Abdominal ultrasound: evaluate pyelectasia, ureteral obstruction
- Blood work- ionized calcium, bile acids as indicated
- Urinalysis: helps with diagnosis of stone type and monitoring medical management
- Urine culture: essential in management and prevention of recurrence
- Struvite: Dissolution diet and long-term antibiotics
- Can take up to a year to fully dissolve stones
- Calcium oxalate: Prevent with diet, dilution, vitamin B6, potassium citrate
- Others: cysteine vs. urate
When to intervene?
- Chronic urinary tract infections
- Worsening azotemia
- Massive stones causing renal parenchymal damage
- Ureteral obstruction(s)
- Surgical Nephrolithotomy: known to decrease renal function in both cats and dogs post-operatively
- Nephrotomy: not ideal as want to maintain/preserve kidney function
- Pyelectomy: potential for obstruction and scar formation
Minimally invasive interventions:
- ESWL: Extracorporeal Shock-wave Lithotripsy
- 85% successful stone removal
- 30% need repeated procedures, 10% have ureteral obstructions
- Can cause renal damage in dogs
- Not suitable in cats due to mobility of kidneys
- Does not fracture cystine stones
- ENL: Endoscopic guided nephrolithotomy
- Standard of care in human medicine for complex nephroliths
- Reduced nephron damage, complete stone removal, ureteral stent placement to prevent ureteral obstructions
- Well tolerated, minimal morbidity and no mortality
- 100% successful stones removal
- Ureteral stents placed at the time of procedure- 0% occurrence of ureteral obstruction
- Serial radiographs: 1/month after procedures then every 3 months for 1 year and every 6 months for life.
- Serial urine cultures and urinalyses
Pre-ENL VD radiograph in a dog, showing of a struvite/calcium apatite nephrolith.
VD radiographs following ENL showing absence of stone and ureteral stent in place.
Shown below is a schematic image of kidney with and percutaneous access with a sheath to allow access via endoscopy in order to remove stones. Nephroscopes are typically used with specialized lithotripsers to simultaneously break up and suction fragments of large stones.
Branter, EB, Berent, AB,, Weisse, CW. Endoscopic assisted nephrolithotomy in cats and dogs. Abstract presented at ACVIM forum 2012.
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