When obstructive urolithiasis occurs in goats, surgical intervention may be needed

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Obstructive urolithiasis is a common, painful, and life-threatening problem affecting male goats. Typical presentations include complete or partial urethral obstruction. The patient is observed to posture, strain to urinate, vocalize, and might have a diminished appetite with prolonged recumbence. The severity of the patient’s distress and pain is often related to the extent of obstruction. Complete urethral obstruction may progress to urethral rupture or bladder tearing with uroabdomen. These sequelae are evidenced by subcutaneous urine pooling or abdominal distension, usually accompanied by lethargy and increased discomfort.

Diagnostics

When obstructive urolithiasis is suspected, bloodwork should evaluate packed cell volume/total solids (PCV/ TS), lactate, creatinine, and electrolyte balance. Although caudal abdominal palpation can confirm a distended bladder and localize pain in small goats, abdominal ultrasound is useful in identifying echogenic kidney, bladder, and urethral calculi; defining the bladder diameter; recognizing free peritoneal fluid; and locating urethral distension. Although examination and ultrasound can confirm the diagnosis, radiography provides a global, localizing view of radiopaque calculi. When urethral obstruction is suspected and radiopaque calculi are not observed, CT scan is useful for evaluating the obstruction.

Treatment

Patients with complete urethral obstruction benefit from placement of a temporary percutaneous bladder catheter (Bonanno suprapubic bladder drainage catheter) for bladder decompression, pain relief, and systemic stabilization. Intravenous fluid resuscitation should be provided to hypovolemic or azotemic patients, and fluid diuresis can be helpful in partially obstructed patients to encourage clearance of calculi. Hyperkalemia is an indication for treatment with a combination of calcium, dextrose, and insulin. Analgesia should be provided with consideration to the patient’s renal health. Although most elevations in creatinine represent a postrenal azotemia, nonsteroidal anti-inflammatory drugs are avoided until the patient’s creatinine has normalized.

In cases of acute partial obstruction, medical treatment with analgesics, urine acidifying agents, and supportive fluid supplementation can occasionally be successful. Chronic partial obstruction might result in urethral and bladder injury that prolongs or complicates the patient’s recovery.

The decision for surgical intervention is based on the location and extent of obstruction, duration of partial obstruction, and systemic health. Anatomic features of the goat urinary tract that amplify the problematic nature of the long, narrow male urethra include the vermiform appendage (VA), and sigmoid flexure. Urethral diverticulum, a urinary tract condition in goats, also affects the urethra. Additionally, young animals or those castrated at an early age can have a vermiform appendage adhered to the free penis and folded caudally at an acute angle.

Figure 1. Penis exteriorized for excision of the vermiform appendage.

The first line of surgical intervention is excision of the vermiform appendage. Sedation, local anesthesia, or epidural administration, along with rumping or lateral positioning with the hind limbs pulled cranially, can facilitate exteriorization and transection of the VA. Allis forceps and dry gauze sponges are useful implements for grasping the preputial lamina or penis (Figure 1). Although VA excision might resolve the obstruction, the presence of cystoliths frequently contributes to rapid recurrence of urethral obstruction.

Figure 2. Urethrotomy for removal of numerous calcium carbonate ureteroliths.

A tube cystotomy, sometimes in combination with a urethrotomy, is the major surgical treatment for obstructive urolithiasis. Key aspects of this procedure include thorough removal of cystoliths and urethral hydropulsion to relieve or identify an unresolving obstruction. The urethral diverticulum usually prevents retrograde catheterization of the bladder and can trap calculi retropulsed from the distal urethra. Although the sigmoid flexure straightens when the penis is exteriorized, it is a common location for urethral obstruction. Large, numerous, or tightly packed calculi are unlikely to dislodge without a urethrotomy or lithotripsy. Careful palpation, localization with urinary catheters passed retrograde and normograde, and imaging (eg, ultrasound, radiographs) can confirm the site of persistent obstruction for planning a urethrotomy. A urethrotomy can be performed by isolating the penis and making a midline incision over the calculus of concern, or over a red rubber urinary catheter (Figure 2). A large-gauge Foley catheter should be selected as the indwelling cystotomy tube to limit the risk of catheter obstruction from clots and fibrin. It is secured through the body wall into the bladder with a saline inflated balloon (Figure 3). Postoperatively, a patent urethra and body wall adhesion should be confirmed prior to Foley catheter removal.

Figure 3. A Foley catheter is inserted through the body wall and into the bladder, where it is secured by saline inflation of the balloon and a purse-string suture in the bladder.

Patients presenting repeatedly for obstructive urolithiasis that have extensive urethral obstruction or that have developed distal urethral injury could be candidates for a perineal urethrostomy (PU). The urethra is spatulated below the anus to decrease urethral length and increase the luminal diameter at its exit. Hemorrhage is the major intraoperative risk during dissection of the penis, so the procedure is facilitated by electrocautery and suction. Careful apposition of the mucosa and skin can decrease the risk of stoma stricture. Another common complication, urine scald, can be avoided or treated by crescent-shaped skin excision and advancement flaps abaxial to the PU. This technique removes redundant tissue that impedes the urine trajectory in obese goats.

Procedures like bladder marsupialization or vesicopreputial anastomosis could also be appropriate for goats with recurrent obstructive urolithiasis; however, stoma stricture and ascending cystitis are complications of both. Additionally, serious risk of profound urine scald accompanies bladder marsupialization. These procedures are end-stage treatments as reversal is unlikely to be feasible or functional.

Regardless of treatment, retrieval and lab submission of uroliths for identification can be beneficial in guiding management recommendations in collaboration with a nutritionist. Goats should be carefully monitored to allow early intervention in case of recurrence.

Rebecca C. McOnie, DVM, DACVS-LA, is an American College of Veterinary Surgeons board- certified large animal veterinary surgeon and clinical instructor at Cornell University College of Veterinary Medicine in Ithaca, New York. She attends to horses and various farm animal species, working with students and resident trainees. She enjoys sports and exploring the outdoors.