Urolithiasis

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Urolithiasis

• Urolithiasis is the main cause of obstruction in the lower urinary tract. Although it occurs in both males and females, urolithiasis is more common in males due to their long, narrow urethra.
  
• Common sites of obstruction in the different species include:

cats - the urethra

dogs - base of the os penis

bulls - the proximal end of the sigmoid flexure or the ischial arch

rams - vermiform appendage

• The most common location for urolith formation is the bladder lumen although they may also occur in the renal pelvis, ureters or urethra.
• Consequences include obstruction, ulceration, cystitis, urethritis, nephritis, hydronephrosis and rupture of the bladder or urethra.
• Predisposing factors include bacterial infection, alterations in pH of the urine, heredity, sex, species and decreased water intake.

Types of uroliths

Struvite

• most common urolith in small animals
• commonly associated with infection by urease producing organisms such as Staphylococcus or Proteus
• more common in females due to increased susceptibility to urinary tract infections
• formation enhanced by the presence of alkaline urine

Calcium oxalate

• form due to supersaturation of urine with calcium
• often have spine-like projections

Urate

• Dalmations predisposed

Cystine

• occurs with cystinuria

Calcium carbonate

• occurs in horses

Silica

• occurs in pastured ruminants
• development of may be related to diet

Definitions

Urolithiasis - the presence of calculi, or uroliths, in the urinary passages.
Urolith (calculus, stone) - polycrystalline concretion of precipitated urinary solutes, urinary proteins and proteinaceous debris.