Urolithiasis refers to stone formation in the urinary tract. Stones form from the aggregation of minerals and proteins in urine. They have a central protein core surrounded by mineral layers. Stones most commonly cause obstructions in the male ureter. This leads to pressure necrosis, ulceration, and hemorrhagic urethritis at the site of obstruction. Urolithiasis occurs frequently in cats, dogs, and ruminants but rarely in horses and pigs. The causes include urinary pH, dehydration, diet deficiencies, inflammation, inherited metabolic disorders, and bacterial infections. The main types of stones are struvite, calcium oxalate, urate, and cystine stones.

1. Urolithiasis

2.  Aggregations of sedimented urinary
solutes (minerals, proteins)
 Central nidus (usually protein),
surrounded by laminar ”stone” and
surface crystals
Uroliths

3.  Causes obstructions usually in males’
ureter
 At the site of obstruction, there is local
pressure necrosis, ulceration of the
mucosa and acute hemorrhagic urethritis
 Often in cats, dogs and ruminants
 Seldom in horses and pigs

4. Causes
 Urinary pH
 Reduced water intake causes crystallization
 Feeding; for exaple low vitamin A, high
phosphorus in ruminants, magnesium in cats
causes mucosal damage which produces nidi for
the stones
 Inflammation; leukocytes, fibrin, epithelial cells
also serve as a nidus
 Inborn error of metabolism

5. Struvite stones
 Magnesium ammonium
phosphate (MAP)
 Most common type in dogs
 Also in cats and ruminants
 Females are most
commonly affected
 Bacterial ureases -> pH h
-> struvite solubility i

6. Oxalate stones
 consist of calcium oxalate
 development is not well
understood
 caused by hypercalciuria and
hyperoxaluria
 dietary magnesium and citrate
inhibit formation
 common in male dogs and rare
in ruminants (plants -> acute
death), related to diet in cats

7. Urate stones
 contain either ammonium
urate with some uric acid
and phosphate or sodium
urate
 often in male Dalmatians
(inherited)
 incomplete conversion of
uric acid to allantoin in liver
-> uric acid in urine
 also dogs with liver disorders
 portosystemic shunts,
cirrhosis

8. Cystine stones
 Consist of pure cystine
 may also contain calcium
oxalate, struvite and complex
urates
 Occur in dogs, rarely in cats
 Almost exclusively in males
 Inborn error of metabolism
-> defective proximal tubular
reabsorption from glomerular
filtrate -> high levels of
urinary cystine

9. Thanks