Minimizing pseudo-recurrent urolithiasis

Case scenario: A 4-year-old male neutered Dalmatian with a history of ammonium urate urolithiasis was admitted to a veterinary hospital because of clinical signs presumed to be related to obstruction of the urethra caused with uroliths.

DIAGNOTES

The owner had observed the dog unsuccessfully straining to void urine for the past 24 hours. Survey and contrast radiography confirmed the presence of numerous uroliths in the lumen of the urethra and urinary bladder (Figure 1). Using retrograde urohydropropulsion, the urethroliths were returned to the urinary bladder by the emergency staff. As the dog was not azotemic and was otherwise healthy, a cystotomy was performed, and more than 100 uroliths were removed. Analysis of the uroliths revealed that they were composed of 100-percent ammonium urate.

Figure 1: Double contrast cystogram of the dog described in Figure 1. There are three uroliths in the bladder lumen.

At the time the dog was released from the hospital, the owners were advised that a management protocol designed to minimize risk factors associated with ammonium urate uroliths should be seriously considered. This encompassed using a high-moisture (canned) diet designed to restrict purines and to promote formation of dilute alkaline urine (Prescription Diet Canine u/d, Hill's Pet Nutrition).

Twelve days later, the dog was returned to the hospital for removal of abdominal skin sutures. According to the owner, the dog was pollakiuric for the first week following surgery. For the past two to three days, he was dysuric and voided an abnormally small stream of urine.

Jody P. Lulich

Palpation of the dog's urethra per rectum revealed at least two uroliths causing partial urethral outflow obstruction. Follow-up contrast radiography confirmed that three uroliths were present in the urethra. Because the uroliths were smooth, they were readily repulsed into the urinary bladder by retrograde urohydropropulsion. Double contrast cystography revealed that three uroliths were in the bladder lumen at that time (Figure 2). The three uroliths were approximately 0.5 cm in diameter.

Figure 2: Retrograde positive contrast urethrocystogram of a 4-year-old male Dalmatian illustrating numerous ammonium urate uroliths in the bladder and urethra.

This prompted the owners to ask whether or not the stones had reformed during the 12-day post-surgical interval. Unfortunately, postoperative radiographs were not evaluated immediately following the cystotomy to determine if all of the stones had been removed. Study of the biological behavior of urate urolithiasis in Dalmatians indicates that recurrence of uroliths in this patient within the 12-day period following surgery is highly improbable. In our opinion, failure to remove all the uroliths by cystotomy was a medical mistake (e.g. an iatrogenic complication).

Carl A. Osborne

Understanding the cause

How common is pseudorecurrent urolithiasis? Several years ago, we performed a retrospective study of cystotomies performed to remove uroliths from 37 dogs and 29 cats in our veterinary teaching hospital (Lulich J, Osborne C, et al. Incomplete Removal of Canine and Feline Urocystoliths by Cystotomy. J Vet Int Med; 7: 124, 1993). Incomplete removal of uroliths was documented and revealed incomplete removal in eight dogs and four cats. The observation that uroliths were detected in the lower urinary tract following cystotomy in 20 percent of cats and 14 percent of dogs in a teaching hospital with board-certified surgeons on the staff emphasizes an inherent risk associated with this procedure. In our experience, based on consultations with our colleagues in private practice, incomplete removal of uroliths occurs much more frequently than is recognized.

Why? Because radiography of the urinary tract immediately following surgery has not been a standard practice. A common theme is discovery of remaining uroliths several weeks or months following surgery when patients are re-evaluated because of persistent or recurrent signs of lower urinary tract disease. In this situation, delayed detection of uroliths is often erroneously attributed to recurrence (pseudo-recurrence). This, in turn, may result in inappropriate prognostic and therapeutic recommendations.

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Consider the options

How can pseudorecurrent urolithiasis be minimized?

One should consider the following procedures.

• 1. When discussing the option of surgery to remove uroliths from the lower urinary tract, clients should be informed that even in the hands of experienced surgeons, there is a risk that not all uroliths will be removed. Therefore, appropriate radiographs will be evaluated following surgery. Clients also should be informed of the consequences of incomplete removal of uroliths, and the benefits and risks of therapeutic strategies available to manage this complication.

• 2. Uroliths often migrate to lower portions of the urinary tract. Therefore, if several days have elapsed between the date of diagnostic radiography and/or ultrasonography and the date of surgery scheduled to remove the uroliths, the number and location of stones should be re-evaluated by appropriate imaging methods just prior to surgery.

• 3. Appropriate caution should be taken to remove all uroliths from the bladder lumen, bladder neck and urethra. When possible, the number of uroliths removed from the lower urinary tract should be compared with the number of uroliths detected by radiography, ultrasonography or via cystoscopy. Uroliths may be removed with the aid of spoons, forceps, gauze sponges or suction devices. The lumen of the bladder and bladder neck should be explored with a finger to detect remaining uroliths.

In addition, the bladder lumen should be flushed with an isotonic solution to remove subvisual uroliths. Uroliths that have passed into the urethral lumen may be flushed back into the bladder lumen by injecting appropriate quantities of physiological saline through a catheter placed in the external urethral orifice. The external urethral orifice should be occluded around the catheter to facilitate flushing of the urethroliths back into the bladder lumen. If the distal urethra is not occluded, fluid may flow around small urethroliths without moving them into the bladder lumen. This will result in incomplete removal of uroliths.

If retrograde flushing techniques are used to flush urethroliths into the bladder with the aid of a catheter inserted into the distal urethral orifice, appropriate caution must be used to minimize retrograde flushing of bacteria that normally colonize the mucosa of the distal urethra and genital tract into the urinary bladder and surgical site. Inserting a flexible catheter through its lumen via the urinary bladder also may enhance patency of the urethra. Injection of an isotonic solution through the catheter may force uroliths out of the distal urethral orifice. In some cases, it may be of value to check for uroliths by digital palpation of the urethra per rectum. Appropriate precaution should be used to avoid contamination of the surgical site.

• 4. Especially when multiple uroliths are detected prior to cystotomy, re-evaluate the urinary tract radiographically immediately following surgery. Immediate detection of uroliths that were inadvertently left in the urinary tract is of great importance. If they obstruct the urethra before the cystotomy incision heals, life-threatening complications may develop.

If uroliths remaining in the lower urinary tract following surgery are first detected by radiography or ultrasonography several weeks following surgery, it may be erroneously assumed that the patient is highly predisposed to recurrent urolithiasis.

Dr. Osborne, a diplomate of the American College of Veterinary Internal Medicine, is professor of medicine in the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.

Dr. Lulich, a diplomate of the American College of Veterinary Internal Medicine, is a professor in the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.