Bladder, Urethra and Ureters
Equine urolithiasis
Urolithiasis
Horses tend to have a single stone in the bladder. The presenting complaint is hematuria, generally associated with exercise. It is rare for the stone to move more distally than the pelvic urethra. However, if the stone does lodge in the urethra, those horses can develop ruptured bladders. Many horses with bladder stones do have nephroliths, as well.
Bladder stone removal may be accomplished through the urethra (standing) or via cystotomy (general anesthesia). Gradual urethral sphincter dilation and/or sphincterotomy can allow stone removal in mares. Stones in males are often removed via perineal urethrotomy or, less commonly, via a perirectal incision. In both cases, stones may need to be broken up prior to standing removal. Other options include stone buster lasers, laparoscopy and lithotripsy. Standing removal is most common and can be done in the field with proper facilities (stocks are advisable).
Laparocystotomy
Removal of stones via cystotomy under general anesthesia is considered by many to be the procedure of choice. This method allows intact stone removal, culture of the bladder wall, and removal of all stone debris. Leaving stone debris can lead to future obstruction and/or stone formation. However, bladder access is difficult in adult horses and is occasionally impossible. General anesthesia and laparotomy is also the most expensive option with the longest associated recovery period.
Laparoscopic cystotomy
This method of removal has been reported. It does require experience with laparoscopy and specialized instrumentation. The stone needs to be caught in a bag and it is difficult to close the bladder with inverting sutures that don’t penetrate the lumen. Having suture penetrate the lumen predisposes to more stone formation and unhappy client. It is possible to remove stones up to 6-8cm in diameter using this method.
Perineal urethrostomy (males)
Stone removal is performed in the standing animal under epidural anesthesia. Access to the stone is obtained through the PU. The stone is manipulated per rectum and removed via the PU using a grabbing forceps (lithotrite or other). In some instances the stone must be broken up to allow removal. Fragments of stone are often left behind and need to be flushed out to minimize the risk of stone recurrence. Trauma to the rectum, urethra, and testicles (if present) is possible.
Pararectal cystotomy (Gokel’s operation)
This procedure is not often used but may be an economical approach for removing large cystic calculi. It has been recently suggested to be a useful method with lower risks than PU’s. Vet Surg 39:654-659, 2010
Electrohydraulic lithotripsy
Lithotripsy is performed via a PU. The bladder is emptied and the calculus identified via cystoscopy. The lithotripsy probe or lithotrite is passed into the bladder via the urethrostomy and electrical current applied to fragment calculus. The pieces of calculus are removed manually or by lavage. Regular shockwave machines have also been used to do lithotripsy via a special handpiece.
Laser treatment
Pulsed dye or “stone-buster” lasers are used to vaporize stones and allow them to be flushed out. The laser is inserted via a PU. The laser creates a plasma layer at the surface of the stone and the stone disintegrates. These lasers require a fluid medium to work and this can be tiresome in the standing horse (takes a lot of time just to maintain a fluid bath). Lasers can be rented from human hospitals or laser supply organizations. Not much advantage over standing procedures. (Holmium : YAG lasers are cheaper– $500/day vs $1500/day–and work in people but don’t work on many equine stones. These work via a photothermal mechanism.)
Manual removal ± sphincterotomy (females)
Mares aren’t as prone to stones but they do occur. Most can be removed standing.
Method :
- gradually dilate sphincter by inserting one finger, then two, etc
- if need more room, incise sphincter on dorsal and cranial aspect by inserting a blade into the urethra and cutting from inside the urethra out into the vestibule/vagina
- grab stone with lithotrite, using hand in rectum to manipulate stone
- may need to crush large calculi prior to removal
- follow with copious lavage (can use endoscope to see if all debris removed)
- close sphincter (if cut) with monofilament absorbable suture material
Sabulous urolithiasis
This is more a collection of sediment than a true stone. Sabulous uroliths develop due to abnormal bladder emptying. These are poorly responsive to medical or surgical treatment.
Urethral calculi
Urethral calculi are frequently associated with bladder rupture unless a PU is performed. Stones are typically found in the proximal urethra and removal is as for a bladder stone. Distal stones may be removed with a similar incision over the stone or just proximal to it. The procedure is performed under GA in dorsal recumbency. A tourniquet may be applied to assist with hemostasis, particularly with penile stones. The incision is made in through the CSP into the urethra (identified by a urinary catheter). Grasping forceps are used to remove the stone. The surgery site is closed with 3-0 absorbable suture if in the sheath due to the risk of adhesion formation. Other sites may be best left open due to tissue trauma and contamination.
Nephroliths
Removal of nephroliths can be performed via nephrectomy or nephrotomy but is uncommon (these are not usually a clinical problem until hydronephrosis and renal failure). Percutaneous removal has been reported in people. Using fluoroscopy or ultrasonography, a needle is placed through the flank into the kidney. A small guidewire is placed through the needle. The tract is progressively dilated to 24Fr to accommodate a nephroscope. Smaller calculi are removed using forceps or a basket. Larger calculi are fragmented using lithotripsy. The nephrostomy tube is left in place for 3 days.
Ureteral calculi
Ureteral calculi are rare and can cause intensive pain. They may be palpable per rectum just cranial to the brim of the pelvis. Most horses will have renal failure at the time of diagnosis. Pyelograpy, ultrasound, endoscopy (go up the ureter) or scintigraphy can be useful in the diagnosis. Surgical removal can be performed via a paralumbar incision. An alternative is to pass a Dormia basket stone dislodger retrograde from the ureteral orifice. The dislodger is guided by digital palpation into the ureteral orifice and then guided beyond the calculus by a second person palpating per rectum. The basket is opened and retracted to snare the stone. Slow gentle traction is used for removal.
Management for recurrence
Once a stone former, always a stone former”
- recommend biannual examinations to check for stones
- stones are much easier to remove if small and “immature” (not fully calcified)
- it is easiest to detect stones with an empty bladder (catheterize bladder if necessary)
- combine rectal palpation/ ultrasound
- should ultrasound kidneys if cystic calculi found (we may not treat nephroliths but can detect hydronephrosis)
- increase water consumption and urine output
- feed salt (cattle fed salt at 1-2% of ration decreases incidence of stones)
- decrease calcium in diet
- acidifying diets may help dissolve or prevent stones
- it has been extremely difficult to acidify urine in herbivores
- acidic urine may not affect formation of stones in horses (unknown)
- ascorbic acid = oral Vit C; 4000 mg po q12h
- potassium magnesium aspartate 2500 mg po q 12h
- latest : DCAB diets may help – SoyChlor is a ruminant feed additive that does acidify urine in horses
- we don’t know the effects of this diet on equine bone yet but the diet is used to stimulate osteoporosis in sheep
- appears to increase excretion of calcium so probably NOT a good idea in horses
