Specialty Spotlight: Management of Cystic and Urethral Calculi

June 23rd, 2025 | Posted in General, Medical Articles

Specialty Spotlight: Management of Cystic and Urethral Calculi

Davida Rausch, DVM, DACVS-SA

Management of Cystic and Urethral Calculi

Cystic (bladder) and urethral calculi (stones) are one of the most common reasons for surgery to be performed on the urinary tract.  Knowledge of common types of stones is needed to guide therapy, know when surgery is indicated, and evaluate for concurrent disease processes.

Struvite Stones
Struvite (magnesium ammonium phosphate) calculi are one of the most common types of stones and account for approximately 40% of all stones in dogs, and nearly 50% in cats.  Struvite stones are radiopaque and easily seen on radiographs.  These stones are associated with urinary tract infections in nearly 90% of canine cases, but rarely in cats.  Medical management and dissolution of stones (dietary) can be considered if this stone type is suspected.  However, surgical removal of the stones should be considered in males if there is concern for urethral obstruction or if clinical signs are severe.  Infection may not fully resolve until all stones are removed from the bladder.  A urine culture may be beneficial to guide antibiotic therapy.

Calcium Oxalate Stones
Calcium-based stones are the other most common type of urinary tract calculi seen.  These stones often have sharp edges, making them very irritating in the bladder and urethra.  Urinary tract infection may still be present secondary to irritation caused by these stones.  Calcium oxalate stones are radiopaque and easily seen on radiographs.  Calcium levels should always be checked in both cats and dogs with suspected calcium oxalate stones, as hypercalcemia can be an underlying cause.  Hypercalcemia may have a variety of causes such as hypercalcemia of malignancy (lymphoma, anal sac tumors), primary hyperparathyroidism, or idiopathic.  Calcium oxalate stones can also frequently form with normal calcium levels.

Urate and Cystine Stones
These types of stones are much less common but require some special considerations.  These stones are reported to be radiolucent (not visible on radiographs); however, with digital imaging now common, visibility of these stones is much better than in the past with film radiographs.  Ultrasound may be needed to identify the presence of these stones.  Remembering the types of stones that are radiolucent may be easier with the pneumonic I Can’t C (cystine) U (urate).

Urate stones may form due to genetic predisposition in certain breeds (Dalmatian, English Bulldog) or due to excess ammonia secondary to portosystemic shunts in both dogs and cats.

Cystine stones most commonly form in intact male dogs, and occasionally in cats.  They are often slightly more radiopaque than urate stones.  If this type of stone is suspected/confirmed in dogs, castration will often prevent recurrence.  Dachshund, Basset Hound, English Bulldog, French Bulldog, Mastiff, and Rottweiler are some of the reported breeds that have a predisposition to developing these stones.

Surgical Treatment
Cystotomy is the most common surgical technique for the removal of calculi.  Both dorsal and ventral cystotomy techniques have been described; however, ventral cystotomy is easier to perform, provides good visualization, and decreases possible iatrogenic trauma to the ureteral openings.  Absorbable monofilament suture material should be used for closure.  Multiple suture patterns (simple interrupted, simple continuous, 2-layer inverting) have all been described with no difference in outcome.  Accurate needle placement through the submucosal layer, however, is critical.  The most concerning complication after cystotomy is uroabdomen, which will often require additional surgery for identification and correction.

Scrotal urethrostomy may be required for male dogs when calculi are causing an obstruction of the urethra, and are unable to be flushed back into the bladder.  For this surgical procedure, castration is performed if the dog is intact, and an incision is made into the scrotal urethra.  The urethral mucosa is then sutured to the skin, creating a new opening for urination.  While other locations for urethrostomy are reported, the scrotal location gives the most consistent and best results.  This procedure is more technically challenging, and referral should be considered if the practitioner is not familiar with the technique.

Perineal urethrostomy is performed in cats with urinary obstruction.  Although other locations for urethrostomy have also been reported in cats, the perineal location provides a consistently good outcome if proper technique is used.

-Davida Rausch, DVM, DACVS-SA

References

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