Stalking stones: An overview of canine and feline urolithiasis - Veterinary Medicine
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Stalking stones: An overview of canine and feline urolithiasis
Did you know that a new type of urolith has been found in cats? Should you institute preventive therapy if you identify only crystalluria? Is antibiotic therapy automatically warranted in animals with indwelling urinary catheters? This internist revamps your knowledge on diagnosing, treating, and preventing urolithiasis.


VETERINARY MEDICINE



Figure 1A. A lateral abdominal radiograph of a dog examined for the primary complaints of hematuria and dysuria. No uroliths are observed in the urinary tract, including the portion of the urethra that can be seen on the film.
When imaging patients with confirmed urolithiasis or with clinical signs suggestive of urolithiasis, include as much of the urethra as possible since uroliths could be missed (Figures 1A & 1B). Position identification labels and other imaging markers so they do not obscure any part of the urinary tract (Figure 1B).


Figure 1B. A lateral radiograph of the dog from Figure 1A showing the proper positioning of a patient to view the length of the urethra, including the perineal and penile urethra. Note the four radiopaque urethroliths proximal to the os penis (straight arrow). The identification label on the film (curved arrow) may be obscuring a portion of the urethra.
If initial imaging results do not reveal an obvious cause of the patient's clinical signs or are inconclusive, attempt urethral catheterization and perform a retrograde contrast study if necessary. Also, perform a rectal examination to palpate the urethra and rule out other concomitant disorders, such as prostatic disease or urethral neoplasia.


Figure 2. Extending the penis and prepuce away from the body of a sedated or anesthetized cat will facilitate transurethral passage of a urinary catheter.
When catheterizing a patient's urethra, you may note a grating sensation as the catheter moves past small uroliths, or the uroliths may prevent catheter passage. Resistance to catheterization is normal at the base of the os penis and pelvic flexure in male dogs. Successfully catheterizing a male cat typically requires sedation or anesthesia and appropriate extension of the penis away from the patient's body (Figure 2). Occasionally, a urinary catheter may pass by uroliths without indicating their presence, especially when you use a relatively small diameter catheter.


Figure 3. Retrograde positive contrast study in the patient from Figure 1A. Note the filling defects in the urethra where the four uroliths (arrow) seen in Figure 1B are located.
Ruling out urethroliths and, in some cases, urocystoliths may require performing retrograde cystography or urethrography. This imaging technique may also be indicated to help establish the exact location and approximate number of uroliths (Figure 3).

TREATMENT OVERVIEW

If the patient is stable, take steps to determine the likely urolith composition and to develop a treatment plan. If the patient is relatively asymptomatic, monitoring the pet's condition and establishing measures to prevent further urolith formation may be all that is needed.

Relieve urethral obstruction


Antegrade and retrograde urethral urohydropropulsion in male dogs or cats
If the patient is not stable or has a complicating condition or a urethral obstruction, stabilize the patient and resolve the obstruction. Techniques for propulsing urethral uroliths or plugs (macroscopic aggregate of organic matrix and crystals) retrograde into the bladder or antegrade through the urethral orifice are discussed in the boxed text titled "Antegrade and retrograde urethral urohydropropulsion in male dogs or cats."


Placing an indwelling catheter and a connection to a closed urine collection system
If a urethral obstruction cannot be safely resolved in a timely manner, perform cystocentesis to decompress the bladder or place a cystostomy tube to allow a temporary outlet for urine until the obstruction can be eliminated. If the patient is at high risk for reobstruction, has had excessive trauma to the urethra in the process of relieving the obstruction, or has developed an atonic bladder due to prolonged obstruction, place an indwelling urinary catheter with a closed collection system. (See the boxed text titled "Placing an indwelling catheter and a connection to a closed urine collection system.") Avoid placing indwelling urinary catheters indiscriminately because of the increased risk of associated bacterial infection.


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Source: VETERINARY MEDICINE,
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