Urolithiasis
Stones can be located anywhere along the urinary tract - nephrolith, ureterolith, urocystolith, urethrolith.
Signs of urolithiasis may include: - Abdominal pain - Abnormalities of urination (difficulty, frequency, blood) - Straining with the absence of urine (this is an emergency - obstruction) - Anorexia - Vomiting - Depression - Palpation of stone in empty bladder or urethra per rectum
Diagnostics:
Bloodwork If blockage may see post renal azotemia - increased K, P, BUN, creatinine.
Urinalysis Urinary tract inflammation - hematuria, pyuria, may see bacteriuria. Urine pH - struvite crystals precipitate in alkaline urine. Crystals - presence does not mean there are stones, absence does not mean there are not stones. Can be observed in normal individuals.
What is the relationship between stones and UTIs? Stones may lead to infection - mucosal damage, incomplete voiding, bacterial entrapment in stones. UTIs may lead to stones - urease producing bacteria can alkalinize urine.
Radiographs Stones only visible if >1mm in diameter. Generally radiopaque (visible on radiograph) - struvite and calcium oxalate. Asses bladder size - evidence of obstruction? Ultrasound is superior for detection as it detects all types of stones (urate, cystine, and calcium phosphate may not show up on radiograph).
Above is a lateral view demonstrating stones within the bladder. A V/D was also obtained. Always take at least two views. This patient presented for increased frequency of small amounts of urine.
Types of stones:
Struvite Accounts for 50% of canine stones and 30% of feline stones. UTI may predispose to the formation through acidification of the urine.
Calcium Oxalate Accounts for 35% of canine stones and 50-70% of feline stones.
Urate Seen in dogs with portosystemic shunts - high excretion of ammonium biurate crystals. Seen in dalmations - defective hepatic transport of uric acid. My not show on radiographs - show up on ultrasound.
Cystine Inherited disorder - excessive elimination of cystine in the urine. Most commonly seen in male Dachshunds between age 3-6. Stones may show faintly on radiographs - show up on ultrasound.
Silicate Linked to consumption of large amounts of corn gluten and soybean hulls (high in silicates).
Treatment:
Treatment largely depends on the presentation of the patient. Medical management is not suitable for many patients (obstruction occurring or imminent, stone type not known, very large stones, sharp stones etc). If obstructed, emergency intervention is required.
Medical Management Calcium oxalate, urate, cystine, and silicate stones CAN NOT be dissolved and require surgical removal. Struvite stones can occasionally be dissolved with a special diet.
Surgical Treatment Stones may be removed surgically. Surgery varies depending upon the location of the stone. Bladder stones are removed via cystotomy which is often performed in general practice. Stones should be sent away for analysis to determine the appropriate steps moving forward (ie diet).
Above is an exposed bladder at the start of a cystotomy procedure. The patient was only passing small amounts of urine. Over 300ml of urine was removed from the bladder before an incision was able to be made.
Above is the same bladder after emptying the urine via cystocentesis, before incision.
Above are the stones that were removed from the bladder and urethra. The largest stone pictured was located within the urethra, causing a partial obstruction. The stones were sent away for analysis.
Aftercare Many of these stones have a high occurrence rate. Prevention with the appropriate prescription diet is essential. Treatment of concurrent urinary tract infection is essential. Appropriate monitoring is helpful in guiding recommendations moving forward - ie follow up urinalysis.
