Discussion

Occurrence and diagnosis:
Urinary calculi are not common in equids, with a reported prevalence between 0.04 and 0.5% (Laverty et al. 1992). However, most equine practitioners will diagnose urinary calculi more than once over the course of their career. The majority of uroliths are composed of calcium carbonate and can either be spiculated or smooth. Clinical signs typically can include dysuria, haematuria and tenesmus; less frequently complete urinary tract obstruction is observed. Males are more frequently affected likely due to the length and narrow diameter of the urethra. Most uroliths are located in the bladder or urethra; however, uncommonly they are also diagnosed in the kidneys and/or ureters. Diagnosis is made with a combination of transrectal palpation, ultrasound and cystoscopy. Preoperatively it is recommended to identify concurrent issues which may predispose the horse to the development of uroliths, such as pyelonephritis, which can affect prognosis and risk of recurrence (Schott 2002). With that in mind, complete blood count, serum biochemical analysis, renal ultrasound and urinalysis with bacterial culture and sensitivity should be considered.

Treatment:
Surgical removal is the treatment of choice, and options include general anaesthesia and laparocystotomy (Beard 2004), removal through the urethra under epidural anaesthesia (Menendez and Fitch 2012), sphincterotomy (Laverty et al. 1992), pararectal cystotomy (Abuja et al. 2010), laparoscopic cystotomy (Ragle 2002, 2009), laparoscopic assisted cystotomy (Rocken et al. 2006) and lithotripsy (laser or shockwave) (Judy and Galuppo 2002; Grant et al. 2009; Rocken et al. 2012). In mares most small (<5 cm) uroliths can be removed through the urethra with or without a sphincterotomy. Geldings and stallions present more surgical challenges. Determining the best method for surgical removal needs to be assessed on a case by case basis, and factors such as patient compliance, underlying cause, available equipment, urolith size, location and composition need to be taken into consideration. Immediate post operative management will depend on the surgical removal technique, but should include antimicrobials (based on urinary culture results and pharmacokinetics), anti-inflammatory therapy and appropriate incision care. If any urolith fragments remain in situ, bladder lavage needs to be considered, taking into consideration size and location of any performed cystotomy. Possible intraoperative and post operative complications will vary with the surgical technique used, but can include rectal perforation, peritonitis, uroabdomen, urethral trauma with possible stricture, complications with incision healing including infection/dehiscence/herniation, urine pooling and urolith recurrence.

Long-term post operative management:
In my experience, the most common complication following surgical removal is recurrence. Recurrence is most likely related to inherent host factors, incomplete removal of fragments and failure to identify and remove nephroliths/ureteroliths present at the time of surgery. Post operative management with a view to reduce the risk or recurrence of urolithiasis is therefore theoretically important. Management strategies to acidify the urine and dietary manipulation to reduce calcium intake continue to be the mainstay of post operative strategies (Ragle 2009). It should be noted that efficacy of the above strategies remain questionable. Unfortunately there is limited scientific evidence available as to how long these strategies should be maintained and how effective they really are. Regular rechecks to monitor for recurrence should be encouraged as removal of small uroliths is less complicated. Increasing water intake, weight reduction and regular exercise have also been suggested to reduce urolithiasis in horses (Ragle 2009).