Successful management of canine uroliths

Key points

• The most plausible explanation for recurrence of calcium oxalate uroliths within days to months following cystotomy is incomplete surgical removal of uroliths during the previous surgery.
• Recurrence of small uroliths in the urinary bladder can be removed non-surgically by voiding urohydropropulsion.
• Most clients lack the training and experience to appropriately collect urine at home. Don’t waste time relying on these inappropriate samples for making accurate medical decisions.
• Dogs at risk for both struvite (and calcium phosphate carbonate) and calcium oxalate uroliths can be successfully managed by modifying the diet to minimize calcium oxalate and by controlling urinary tract infection to minimize struvite.
• Recommendations to prevent urolith recurrence is just a keystroke away. Go to http://www.cvm.umn.edu/depts/minnesotaurolithcenter/home.html. Our Online system provides easy stone submission for analysis, electronic retrieval of results, easy step by step recommendations to assist in urolith management, and videos of procedures including voiding urohydropropulsion. We even have an App for that-MN Urolith, but you will have to register on line for full use.

Uroliths are solid concretions (stones) that form in any portion of the urinary tract. Urolith formation is abnormal because the urinary system is designed to dispose of liquid wastes not solid stones. However, during urolith formation, sustained alterations in urine composition promote supersaturation of one or more substances eliminated in urine that results in their precipitation and subsequent growth. The degree of urine supersaturation is influenced by the renal excretion of crystalloids, the renal excretion of water, urine pH, and other factors that inhibit crystal formation and crystal aggregation. Urolithiasis should not be viewed conceptually as a single disease with a single cause, but rather as a sequela of multiple interacting physiologic and pathologic processes that progressively increase the risk of precipitation of excreted metabolites in urine to form stones. Therefore, detection of urolithiasis is only the beginning of the diagnostic process. Essential to urolith prevention is identification of their composition and the diseases and risk factors underlying their formation, retention and growth. Regardless of the process of urolith formation, uroliths have the potential to disrupt normal urinary tract function. The mere presence of uroliths in the urinary system does not always necessitate their removal; however, those resulting in clinical signs (dysuria, hematuria, urinary tract infection, incontinence, obstruction, or azotemia) should be appropriately managed.

When should urolithiasis be included in your list of differential diagnoses?

Clinical signs associated with urolithiasis vary depending on location of uroliths in the urinary tract and the degree to which uroliths disrupt normal urinary tract function. Hematuria and pollakiuria are common signs of lower urinary tract disease associated with uroliths in the urinary bladder. However, some dogs and cats with urocystoliths are asymptotic. Uroliths lodged in the urethra may cause more severe and persistent dysuria. Urethroliths resulting in complete urethral obstruction may present with life threatening post-renal azotemia.
Most patients with kidney stones are asymptotic or present for persistent hematuria. Complete unilateral ureteral obstruction can also be asymptotic if the contralateral kidney has sufficient function to maintain serum biochemical homeostasis. Nonspecific pain is inconsistently reported in patients with ureteroliths.

What tests are essential for detection of urolithiasis?

Abdominal palpation is not a reliable method of urolith detection. For example, in one study of 30 episodes of urocystolithiasis in cats, stones were detected by palpation in only 3 (10%). Likewise, it is not possible to detect uroliths located in the renal pelvis by palpation through the abdominal wall. Therefore, radiographic (survey or CT) or ultrasonographic evaluation of the urinary tract is required to detect uroliths consistently.
The primary objective of radiographic or ultrasonographic evaluation of patients is to verify urolith presence, location, number, size, density and shape. Radiographs should include all portions of the urinary tract. As a reminder, imaging the urethra usually requires taking radiographic views more caudal than for routine abdominal evaluation.
The radiographic or ultrasonographic appearance of uroliths is influenced by urolith size, mineral composition, location, and number. Most uroliths greater than 3mm have varying degrees of radiopacity and therefore can be detected by survey abdominal radiography. Uroliths less than 3mm in size may not be visualized unless very dense. Double contrast cystography can be used to enhance resolution of uroliths. Compared to radiographic density of soft tissue, uroliths composed of magnesium ammonium phosphate, calcium oxalate; calcium phosphate, silica, and cystine are often radiopaque. Those composed of urate and cystine are usually radiolucent, and are often not detected by survey radiography unless they are larger.
However, crystalluria is not synonymous with urolith formation. Crystalluria can be observed in patients without uroliths, and absent in patients with uroliths.

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