Bovine Urolithiasis

Chapter 19
Bovine Urolithiasis


Katharine M. Simpson1 and Robert N. Streeter2


1 College of Veterinary Medicine, Ohio State University, Columbus, Ohio, USA


2 Department of Veterinary Clinical Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, Oklahoma, USA


Introduction


Obstructive urolithiasis is a costly and challenging disorder of male ruminants that can be associated with significant morbidity and mortality in affected animals and can have devastating effects on breeding soundness in bulls. The variety of clinical presentations and diverse classes of livestock affected allow for many treatment options. The most appropriate means of therapy will depend on the location and duration of obstruction, intended purpose of the animal, and economic considerations.


Pathophysiology


Uroliths are composed of an organic matrix or nidus combined with mineral salts.1,2 Initially, soluble minerals precipitate into an insoluble crystallized matrix, and ultimately form calculi.3 The composition and concentration of minerals available to contribute to urolith formation are a product of diet, environment, and management. Inflammatory, cellular, or necrotic debris may provide a nidus for calculi development,4 but is uncommon in ruminants.


High-concentrate diets often contain low calcium to phosphorus ratios and frequently result in phosphatic calculi (calcium, ammonium, magnesium),3 most commonly struvite.5 Feedlot and show animals on grain-based rations are therefore at risk.3,4 Pastured cattle grazing western grasses with high levels of silica are at risk of developing silicate uroliths, even after they have stopped consuming the offending forages. Oxalate- and carbonate-containing calculi are less commonly encountered in bovines.3


Inadequate water intake also predisposes to development of urolithiasis. Clinical disease may be precipitated by decreased water availability or consumption, and a seasonal influence has been reported.6 In the winter, decreased voluntary intake or frozen water sources may be problematic.4 Dehydration following high ambient temperatures and lack of available palatable water sources may occur in the summer, particularly in drought conditions.3


Normal pH of ruminant urine is 7 or greater, a physiologic factor that can contribute to calculogenesis as some types of uroliths precipitate in alkaline urine (struvite, calcium phosphate, calcium carbonate).3 Urine pH does not appear to affect silicate calculi.1,3


Both steers and intact bulls are predisposed to urinary obstruction from urolithiasis because of their long and relatively narrow urethra compared with females. Castration at an early age results in a decreased urethral diameter2,7 and increased likelihood of obstructive urolithiasis; steers 8–12 months old are reported to be at highest risk of clinical disease.4 Delaying castration until the animal is at least 6 months of age is therefore recommended by some authors,2,4,7 but welfare concerns regarding late castration should be taken into consideration before implementing this practice. In cattle, urinary obstruction most commonly occurs at or near the sigmoid flexure, although more proximal obstructions are occasionally seen. Multiple uroliths and cystoliths may be present, particularly with phosphatic calculi.3,8 Silica-containing uroliths are usually singular.3 Ureteroliths and nephroliths can also occur but may be less common in cattle than small ruminants; however, one report in grass-fed dairy cows describes ultrasonographic detection of renal calculi in 63% of pastured cattle and 93% of cows in tie stalls in Japan.9


While the prevalence of obstructive urolithiasis is relatively low in mature breeding bulls,4 urothelial injury secondary to obstruction or surgical treatment can be catastrophic to breeding soundness in these animals. Additionally, erection failure from vascular obstruction of the corpus cavernosum following obstructive urolithiasis has been reported in ruminants.10


Clinical findings


Clinical signs vary depending on the stage of the disease process. Frequent posturing to urinate, tail swishing, dysuria, stranguria, hematuria, and partial to complete anuria may be present initially. Blood or calculi are sometimes visible on the preputial hairs (Figure 19.1). Careful palpation of the penis immediately caudal to the scrotum or its remnant may reveal the location of large urethral calculi. Pain may be elicited when the site of obstruction is palpated, but is not consistent. Nonspecific signs including decreased appetite to complete anorexia, hypodipsia, depression, and lethargy may also be apparent or reported by the owner.

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Figure 19.1 Urethral calculi visible on preputial hairs.


Acute urinary obstruction can result in colic signs including bruxism, stretching, treading the hind feet, or kicking at the abdomen. Cattle with acute urethral obstruction may display urethral pulsations ventral to the anus without concurrent urination; these may be palpable per rectum along with a distended urinary bladder. Signs of colic or dysuria typically resolve following urethral or urinary bladder rupture, and clinical improvement may be seen initially followed by signs consistent with uremia.11 Rupture of the urinary tract usually occurs within 48 hours of complete obstruction.


Ruptured urethra results in peri-penile subcutaneous swelling that is cool to the touch and pits on digital pressure; this can extend from the base of the scrotum cranially to involve the entire ventrum (Figure 19.2). If left untreated, necrosis of the affected tissues occurs followed by sloughing.12 Bilateral ventral abdominal distension with a fluid wave on ballottement is suggestive of ruptured urinary bladder11 and resultant uroabdomen. Rectal examination usually reveals a small, partially filled urinary bladder.13 Intact males more commonly rupture the bladder rather than the urethra because of a more substantial tunica albuginea; scrotal hydrocele may result from uroabdomen. Cattle with ruptured urinary bladders can survive for 2 weeks or more following cystorrhexis.14 Although rare in ruminants, ureteral calculi may be palpable per rectum.15

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Figure 19.2 Subcutaneous peri-penile swelling typically extends from the base of the scrotum cranially and involves the entire ventrum.


Diagnostics


A presumptive diagnosis can usually be made based on history and physical examination findings, including palpation of the penis and rectal examination when possible. If urine can be obtained, urinalysis with examination of sediment should be performed to confirm the diagnosis. Hematuria, proteinuria, and alkalinuria are expected findings. Crystalluria is variably present; determination of crystal type assists with formulation of a treatment plan and prognosis. Concurrent bacterial cystitis or pyelonephritis can contribute to the development of urolithiasis and should be ruled out. In valuable animals, a serum biochemistry profile is recommended and may reveal azotemia, hyperphosphatemia, hypocalcemia, or metabolic acidosis.14 Hyponatremia and hypochloremia are usually present following urinary bladder rupture14,16 but hyperkalemia is not common in cattle.14,17


Transcutaneous and transrectal ultrasonography are useful for assessing the integrity of the urinary tract, the location of obstructing uroliths and the presence of cystoliths, ureteroliths, or nephroliths in the proximal urinary tract, and for indicating the existence of uroabdomen, hydroureter or hydronephrosis. Peri-penile edema may suggest early urethral rupture and signify a lower prognosis. Ultrasonography of bovine urinary tract disorders has recently been reviewed.18 If uroabdomen is suspected, abdominocentesis and comparison of abdominal fluid creatinine to serum creatinine should be performed. A ratio of 2 : 1 or greater confirms uroabdomen.11,19


If uroliths can be acquired, analysis allows determination of calculi type; although not immediately available, this information can guide management strategies to minimize likelihood of recurrence and to prevent additional cases in the herd. In the short-term, placing one or two uroliths in an acidifying agent to establish whether they will dissolve allows the clinician to determine if chemolysis would be an effective adjunctive therapy. Survey or contrast radiography is unlikely to be diagnostic unless the patient is a young calf. However, urethroscopy may be useful for assessing the location of the obstruction, extent of urothelial damage and presence and location of strictures, and for providing additional avenues of treatment.


Treatment


When formulating a treatment plan in cases of obstructive urolithiasis, the clinician should take into consideration the intended use of the animal, integrity of the urinary tract, location of the obstruction or obstructions, and economic constraints. If severe electrolyte, acid–base, or fluid imbalances exist, these should be corrected prior to sedation or anesthesia. Analgesia and antimicrobial and anti-inflammatory drugs are indicated. Meat withdrawal times and degree of renal compromise should be considered prior to drug administration. In cases where the urinary tract is still intact, caution should be exercised during restraint as fractious or struggling animals are at risk of urinary bladder rupture.


Medical treatment


In cases of acute urethral obstruction, relaxation of the retractor penis muscles may allow extrusion of calculi by straightening the sigmoid flexure. This may be accomplished by local anesthetic blockade via a pudendal or ischial penile nerve block.20 Phenothiazine tranquilizers may decrease urethral spasm21 or induce relaxation of the retractor penis muscles,22,23 allowing the calculi to pass. The α2-adrenergic agonists including xylazine are not recommended due to marked diuretic effects.


If penile extrusion can be accomplished with these procedures, retrograde urethral catheterization can be attempted. This is more easily done standing in mature bulls rather than castrated or prepubertal animals and may be hastened by massage per rectum. Infusion of a small volume of lidocaine may be used to decrease urethral spasm following successful catheterization. Gentle urohydropulsion can be used to attempt to dislodge calculi; this may be facilitated by having an assistant manually occlude the pelvic urethra during hydropulsion to maximize urethral expansion at the level of the obstructing urolith. In our experience hydropulsion in cattle is usually unsuccessful, likely due to the relative chronicity of most cases when presented and the resultant periurethral swelling and necrosis. Multiple or forceful attempts at either catheterization or hydropulsion should be avoided due to the risk of urothelial trauma or rupture and resultant stricture or fistula formation, respectively. If the obstruction is not rapidly relieved, surgical intervention is necessary.


Surgical treatment


Acute urethral obstruction in salvage animals


In a commercial or salvage animal, perineal urethrostomy is the most cost-effective method of reestablishing urinary patency. This surgery can be performed low (immediately caudal to the sigmoid flexure) or high (ventral to the rectum at the level of the tuber ischii). It is of paramount importance that the procedure be performed proximal to the level of the urethral obstruction. Careful palpation along the penis may reveal the location of the obstruction; alternatively, ultrasonography is very useful in determining the site of obstruction. The choice of technique is generally determined by the size of the animal and the length of time before the animal is marketable.


Perineal urethrostomy

In young or lightweight animals, a low perineal urethrostomy with penile amputation is commonly performed as it is a more permanent technique that allows for resolution of azotemia and continued growth of the animal prior to slaughter. This is sometimes referred to as “penile transposition” and various methods of performing this technique have been described.13,15,24,25


Surgery can be performed standing with caudal epidural anesthesia and local infiltration of lidocaine, or in dorsal recumbency with lumbosacral epidural and heavy sedation or general anesthesia. The region from the scrotum to the anus is aseptically prepared. A 10–15 cm incision is made on the midline immediately caudal to the scrotum and extended through the fascia between the semimembranosus muscles.15 The paired retractor penis muscles are encountered and can be misidentified as the penis. The penis is grasped and elevated to the level of the skin with a combination of blunt dissection and traction, and the retractor penis muscles may be retracted or be ligated proximally and removed. The dorsal vessels of the penis are ligated, and penile amputation is performed 5 cm distal to the dorsal apex of the skin incision.13 The penis distal to the amputation may be removed or left in place. Removal of the distal penis is facilitated in cases of urethral rupture with subsequent peri-penile tissue necrosis and its removal eliminates a potential source of infection.25 In cases involving an obstructed but not ruptured urethra, sharp dissection of the preputial attachments is required to extirpate the distal penis. If the distal penis is to be left in place, the dorsal penile artery and vein should be reflected from the penile stump rather than ligated. The stump is sutured to the skin using nonabsorbable monofilament suture material in a horizontal mattress pattern through the corpus cavernosum, taking care not to incorporate the urethra. The penis should not be rotated when it is exteriorized and secured to the skin so that the urethra remains on the dorsal surface.15 Spatulation of the urethra is optional. If elected, the urethra is incised to the apex of the skin incision, and the urethral mucosa and tunica albuginea are sutured to the skin using 2-0 monofilament suture in a simple continuous or interrupted pattern. Depending on the procedure, the skin is routinely closed distal and/or proximal to the urethrostomy. In animals that will not be salvaged for several months, amputation and removal of the penis with urethral spatulation affords better apposition of the urethral mucosa to the skin15 and is ideal for decreasing the likelihood and rapidity of stricture formation.


In mature animals and bulls, hemorrhage following this procedure may be substantial but can be controlled by placement of a catheter into the urethra that fits securely and compresses the corpus spongiosum. This should be removed in 2–3 days. Low perineal urethrostomy should not be used in animals intended for breeding.


Ischial urethrostomy

In heavier animals that are near salvage weight (≥ 318 kg), high perineal urethrostomy is ideal to allow the uremia to resolve over approximately 30 days until the animal is suitable for slaughter.12 This procedure is done standing with a caudal epidural for local analgesia. The perineal region from the anus to the base of the scrotum is aseptically prepared.3 A 10-cm midline incision is made starting 5 cm below the anus, over the ischial arch.3 The dense layer of fascia overlying the retractor penis muscles is incised and the muscles exposed.3 Blunt dissection between the retractor penis muscles reveals the bulbospongiosus muscle.3 The urethrotomy is made through the bulbospongiosus muscle or just distal to its attachment.15 When performing this surgery, it is critical to ensure the incision into the urethra is made on the midline in the event that bulging of the urethra is not palpable following dissection down to the penis. Hemorrhage from the corpus spongiosum in the region of the urethral diverticulum is expected and may appear excessive to individuals performing this procedure for the first time. Following high perineal urethrostomy, a 20–28 French Foley catheter is advanced into the bladder and sutured in place where it exits the skin. This can be facilitated by inserting a rigid stylet with a slight curve on the end into the lumen of the Foley. The balloon is distended with saline and retracted until it is seated within the bladder trigone. No sutures are placed into the urethra with this technique. A one-way valve utilizing the fingertip of a surgical or examination glove with a slit cut into the end should be affixed to the external end of the catheter to minimize bacterial contamination and air aspiration into the bladder. This surgery can also be utilized in cases where a previous low perineal urethrostomy has strictured or reobstructed.


Following surgery, a section of inner tubing or impervious plastic should be adhered to the skin just ventral to the anus to prevent fecal contamination of the surgical site.


Urethrotomy

Urethrotomy can be used in cases of acute urethral obstruction (without urethral rupture) provided the location of the calculus is identified via palpation, catheterization, or ultrasound. Following caudal epidural anesthesia, aseptic preparation and local infiltration of 2% lidocaine, an incision is made immediately cranial or caudal to the scrotum and the penis is visualized. The urolith is identified and the affected segment of the penis is exteriorized. Towel clamps or tissue forceps may be used to attempt to crush the calculus. Phosphatic calculi tend to be soft and less amenable to fracture.15 If unsuccessful after two attempts, urethrotomy should be performed immediately distal to the obstruction through relatively healthy urothelium. Most authors recommend primary closure of the urethra,13,15,25 usually with 3-0 absorbable swaged-on suture in a simple interrupted pattern. Urethral closure can be facilitated by suturing over a catheter. Routine closure of the subcutaneous tissues and skin are performed. Urethral dehiscence, stricture, and peri-penile adhesions are common following this procedure, particularly if urethral mucosa is devitalized. Postoperative urinary diversion via cystostomy tube or ischial urethrostomy is ideal for reducing the likelihood of dehiscence or fistulation at the urethral incision site. Alternatively, short-term (24–48 hour) postoperative urethral catheterization may be utilized.


Acute urethral obstruction in breeding animals


If medical therapy and hydropulsion are not successful at relieving the urinary obstruction, certain forms of lithotripsy (including Ho:YAG laser,26 extracorporeal shockwave,27 electrohydraulic shockwave28) or basket catheter retrieval29,30 are less invasive methods of resolving obstructive urolithiasis that may be available at referral centers. If these modalities are not available, a number of surgical options exist. Tube cystostomy with or without cystotomy would be considered the ideal surgical treatment in breeding animals. Urethral surgery is ideally avoided in bulls intended for breeding because of the risk of stricture or fistula formation at the incision site or adhesions of the penis if performed distally.


Laser lithotripsy

Laser lithotripsy has been successful in establishing urethral patency in a steer, goats, and pot-bellied pigs.26,31 Retrograde passage of an endoscope and laser fiber is possible in standing bulls with pudendal nerve block or in recumbent animals under general anesthesia. Normograde urethroscopy and laser lithotripsy may also be performed through the fistula created by tube cystostomy if the endoscope is long enough. Alternatively, the endoscope can be advanced through an ischial urethrotomy site distally to the level of the calculi.


Laser lithotripsy requires an endoscope with at least one instrument port. We have used a similar technique as previously described.26 Prior to urethroscopy, a catheter extension set can be attached to the instrument port. A needle is used to puncture the rubber port that feeds directly into the instrument channel, and a silica optical fiber is fed into the channel until it is only a few millimeters from the channel exit. The fiber is then connected to a holmium:yttrium–aluminum–garnet (Ho:YAG) laser. A 60-mL syringe filled initially with 1% lidocaine is attached to the extension port to allow for local anesthesia, flushing of urethral debris, and hydropulsion via the same instrument channel that the laser fiber occupies. The fiber is then advanced and visualized until it comes into contact with the urolith; it should be centered directly on the stone (Figure 19.3). The laser is fired in a pulsatile manner, with urethral flushing between firing, until the calculus fractures into fragments small enough to dislodge with hydropulsion or retrieve with a wire basket catheter.32 Calculi that are firmly wedged into the urethra are most amenable to laser lithotripsy because they do not move when contacted by the laser fiber.32 Additionally, calculi with irregular surfaces are reportedly less likely to deflect the laser fiber into the surrounding soft tissues than smooth spherical calculi.32 Clinical experience suggests that previous chemolytic treatment in animals with surgical urinary diversion (tube cystostomy, ischial urethrotomy) results in uroliths with uneven surfaces that fracture readily.

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Figure 19.3 Endoscopic image of urolith within the urethra.


Following lithotripsy in animals with an ischial urethrotomy, the endoscope should be passed to the external urethral orifice and the laser fiber or a long guidewire (~280 cm) advanced past the level of the preputial orifice. An assistant holds this in place as the endoscope is removed from the urethra. A transurethral 8–10 French 150-cm silicone Foley catheter (with the distal 2 mm removed) or sterilized polyethylene tubing (200 cm in an adult13) can then be advanced retrograde to the level of the ischial urethrotomy. The fiber or guidewire is retracted until the end is 2–3 mm distal to the end of the catheter and the catheter is advanced into the bladder. The balloon of the catheter is inflated with saline and the catheter secured to the skin of the ventral abdomen with a Chinese finger cuff ligature. A one-way valve is attached to the external end of the catheter. This is left in place for 7–10 days to allow second-intention healing of the urethra and is particularly important if urothelial compromise is present near the level of the previous obstruction. Laser damage to the urothelium can also result in urethral stricture;32 direct mucosal contact or prolonged firing times should thus be avoided. Careful positioning of the laser fiber, good visualization, and adequate irrigation are essential. Cost of equipment usually limits the use of this technology to referral institutions.


Basket catheter and urolith retrieval

Basket catheter retrieval of uroliths has been used to relieve urinary obstruction in bulls while maintaining reproductive capability.30 The procedure can be done standing or in lateral recumbency with sedation or anesthesia. After exteriorization of the penis, the instrument is passed into the external urethral orifice and advanced beyond the level of the obstruction with gentle probing and rotation. The basket is opened and the catheter withdrawn until the calculus is encompassed within.30 The wire basket is closed and the catheter is removed from the urethra.30 If initially unsuccessful, the process can be repeated. Urethral calculi were easily removed in approximately 55% of male calves, via retrograde catheterization with a 5.5 French 70-cm basket stone dislodger and radiography to determine proper catheter placement.29 Surgery was necessary in the remainder of cases. Alternatively, urethroscopy may facilitate appropriate placement of the wire basket. It is suggested that subsequent inflammation in the region of the sigmoid flexure could lead to penile adhesions, which may be circumvented by continued breeding on a limited basis.30


Cystotomy

Cystotomy33 and tube cystostomy34,35 are associated with the best long-term prognosis for survival and reproduction in small ruminants. Urethral surgery and its related complications are avoided, and removal of cystic calculi is facilitated. Disadvantages include the necessity of general anesthesia, cost and duration of surgery, and potential for temporary urethral obstruction from inflammation postoperatively.15


The urinary bladder is exteriorized via a paramedian skin incision adjacent to the prepuce, and either paramedian or midline celiotomy.36 Cystorrhaphy is performed in cases of ruptured bladder. Resection of necrotic regions of the bladder wall may be necessary in cases of rupture following chronic distension. Routine cystotomy is followed by aspiration and lavage of the trigone, bladder neck, and most proximal urethra to dislodge cystoliths. Uroliths adhered to the urinary bladder wall with fibrin or cellular debris can be removed with a soft-edged surgical spoon. Normograde urethral catheterization with an 8–10 French polypropylene catheter and hydropulsion with saline may relieve urethral obstructions but should be done with caution to avoid initiating or exacerbating urethral rupture.34 Retrograde hydropulsion may also be required and can be performed by an assistant; concurrent occlusion of the distal urethra prevents loss of flush solution.36 Occlusion of the proximal urethra by the surgeon maximizes urethral dilation and probability of dislodging uroliths.37 However, excessive time and effort at relieving urethral obstructions via hydropulsion are contraindicated because of the risk of urothelial trauma. If urethral patency is not readily established following cystotomy, tube cystostomy should be performed. The cystotomy is closed in one or two layers with inverting pattern(s) using absorbable suture.36 Celiotomy and skin incisions are routinely closed. Prognosis for survival of cattle undergoing cystotomy and indwelling urethral catheterization is 70%.38


Tube cystostomy

Tube cystostomy provides urinary diversion to allow for relief of urethral spasm and swelling and healing of the urothelium, and offers a direct route for administering chemolytic agents into the urinary bladder15,39,40 (Figure 19.4). Although typically performed with cystotomy, tube cystostomy alone has been successful and shortens the length of the procedure.36 In cattle, this surgery can be performed standing through a laparotomy incision, although optimal access to the urinary bladder is obtained through a ventral celiotomy as previously described. The urinary bladder is visualized and exteriorized. A Foley catheter or similar retention catheter (mare uterine lavage tube, gastrostomy tube) is advanced through the skin via a stab incision opposite the side of the initial skin incision and 3 cm from the prepuce. Use of Carmalt or hemostatic forceps clamped but not locked onto the end of the catheter facilitates placement. The end of the Foley is advanced into the urinary bladder through a stab incision on the cranioventral aspect near the apex; this can be done through a preplaced pursestring suture.15 The balloon is distended with saline to the maximum level recommended. A pursestring suture (if not preplaced) is placed into the seromuscular layer of the urinary bladder around the catheter,15 but should not penetrate the lumen. Tension is placed on the Foley catheter and the urinary bladder is pulled snugly against the abdominal wall.15 Cystopexy to the internal rectus sheath using two to three interrupted sutures can be performed15 if excessive tension is encountered during apposition. Abdominal and skin incisions are routinely closed. A Chinese finger cuff ligature should be placed to secure the Foley catheter to the ventral abdomen, but a pursestring suture should not be placed around the catheter’s exit from the skin, to allow for drainage. A one-way valve is affixed to the end of the catheter. The tube should be left in place for a minimum of 7–10 days. After penile inflammation has subsided, the catheter is intermittently occluded to allow normograde voiding and relief of urethral obstruction. An average of 10–12 days is required for this to occur in small ruminants.34 The tube should remain in place for 24–48 hours following normal urination in the event that reobstruction occurs.15,34

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Figure 19.4 Placement of a Foley catheter in the tube cystotomy procedure.



Courtesy of Rachel Oman.

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Aug 24, 2017 | Posted by in GENERAL | Comments Off on Bovine Urolithiasis

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