Equine Urogenital Injuries Study Guide

Overview and Clinical Importance

Urogenital injuries represent a critical category of equine disorders commonly tested on the NAVLE. These conditions range from life-threatening emergencies in neonatal foals (ruptured bladder) to chronic management challenges in adult horses (urolithiasis). Understanding the pathophysiology, clinical presentation, diagnostic approach, and treatment options is essential for any veterinarian working with horses.

This study guide covers the NAVLE-relevant urogenital injuries including: ruptured bladder in neonates, urolithiasis (urinary calculi), urethral injuries and defects, and parturition-related urinary tract trauma in mares. Each topic emphasizes diagnosis, treatment, prognosis, and high-yield facts for examination success.

Section 1: Uroperitoneum in Neonatal Foals

Definition and Etiology

Uroperitoneum is defined as urine accumulation in the peritoneal cavity secondary to a defect in the urinary tract. In foals, this most commonly results from rupture of the dorsal bladder wall (73% of cases), urachus (22% of cases), or rarely the ureters (5% of cases).

Causes of Uroperitoneum in Foals

Clinical Signs

Foals with uroperitoneum typically appear normal at birth but develop progressive clinical signs within 24-72 hours:

• Lethargy and depression - progressive decline in mentation
• Tachycardia and tachypnea - from hypovolemia and metabolic derangements
• Abdominal distension - fluid wave on ballottement
• Stranguria - frequent attempts to urinate (often mistaken for meconium impaction)
• Scrotal enlargement in colts - urine accumulation through vaginal tunic
• Neurological deficits - due to severe hyponatremia

Diagnosis

Exam Focus: The diagnostic gold standard is comparing peritoneal fluid creatinine to serum creatinine. A ratio greater than 2:1 confirms uroperitoneum. Remember the classic electrolyte triad: hyperKalemia, hypoNatremia, hypoCHLORemia.

Memory Aid - "FOAL RUPTURE": Fluid (abdominal distension), Often males, Azotemia, Lethargy - RUPTURE = Ratio (Cr peritoneal greater than 2x serum), Urination attempts, Potassium HIGH, Tachycardia, Ultrasound confirms, REpair surgically, Electrolyte correction first!

Treatment

Pre-operative Stabilization (CRITICAL)

NEVER proceed to surgery until electrolyte abnormalities are corrected! Hyperkalemia can cause fatal arrhythmias during anesthesia.

• IV Fluid Therapy: 0.9% NaCl (avoid potassium-containing fluids!)
• Abdominal Drainage: Decompresses abdomen and removes urine
• Urinary Catheterization: Prevents further urine accumulation
• Monitor ECG: Watch for peaked T waves, widened QRS, absent P waves

Surgical Repair

Surgical correction via ventral midline laparotomy is the treatment of choice. The defect is identified, edges debrided if necessary, and closed with a double-layer inverting pattern using absorbable suture. Mucosal penetration should be avoided to prevent future calculi formation.

Prognosis

Section 2: Urolithiasis in Horses

Overview and Epidemiology

Urolithiasis has a low prevalence in horses (0.11% of hospital admissions) but causes significant morbidity when present. The condition is more common in males, particularly geldings, due to their longer, less distensible urethra. No breed predisposition has been established. Most affected horses are adults between 7-15 years old.

Urolith Location and Composition

Stone Types

Clinical Signs

The hallmark sign of cystic calculi is hematuria associated with exercise - this is virtually pathognomonic. Additional signs include:

• Dysuria and stranguria - straining to urinate
• Pollakiuria - frequent urination of small amounts
• Urine scalding - dermatitis on hindlimbs from dribbling
• Prolonged penile protrusion
• Colic - especially with urethral obstruction

Diagnosis

• Rectal palpation: Cystic calculi often palpable in empty bladder
• Transrectal ultrasound: Hyperechoic structure with acoustic shadowing
• Cystoscopy: Direct visualization; assess bladder mucosa
• Urinalysis: Hematuria, pyuria; culture for secondary infection
• Ultrasound kidneys: Always check for concurrent nephrolithiasis

Treatment Options

Prevention of Recurrence

Recurrence is common (up to 41% in some studies). Prevention strategies include:

• Dietary modification: Reduce calcium intake; avoid high-alfalfa diets
• Increase water intake: Add salt to diet; ensure fresh water access
• Urine acidification: Ammonium chloride (50-200 mg/kg PO daily) or ammonium sulfate

Section 3: Urethral Defects and Injuries

Urethral Defects Causing Hematuria

Urethral defects (rents) are tears in the urethral mucosa that communicate with the corpus spongiosum penis. They occur at the dorsal convex surface of the urethra at the level of the ischial arch. The cause is believed to be high pressure in the corpus spongiosum during terminal urination (geldings) or ejaculation (stallions).

Diagnosis: Urethroscopy reveals a linear defect on the dorsal convex surface of the urethra at the ischial arch.

Treatment:

• Some cases heal spontaneously with sexual rest
• Temporary subischial urethrostomy: Diverts urine flow, allows healing
• Corpus spongiotomy: Incision into corpus spongiosum without entering urethra

Exam Focus: The timing of hematuria is diagnostic! Hematuria at the END of urination suggests a urethral rent (blood is expelled during terminal contractions). Hematuria THROUGHOUT urination suggests bladder pathology. Quarter Horses may be predisposed.

Section 4: Parturition-Related Urinary Tract Injuries in Mares

Bladder Rupture in Mares

Bladder rupture in postpartum mares is rare (estimated incidence 1:10,000 births) but represents a life-threatening emergency. It occurs due to direct trauma during foaling or compression between the foal and pelvic brim. The bladder may rupture immediately or become necrotic and perforate days later.

Clinical Presentation

Signs typically appear 36-72 hours post-foaling:

• Lethargy, decreased appetite
• Mild to moderate colic
• Tachycardia, tachypnea
• Decreased GI sounds
• May or may not continue urinating normally

Key Point: Same electrolyte abnormalities as foals (hyperkalemia, hyponatremia, hypochloremia, azotemia). Diagnosis and treatment principles are similar.

Surgical Approaches

• Ventral midline celiotomy: Standard approach for ventral/cranial tears
• Standing urethral approach: For caudal/dorsal tears; bladder everted through urethra
• Laparoscopic repair: Minimally invasive option in select cases

Other Urogenital Injuries Associated with Parturition

Section 5: Congenital Urinary Tract Anomalies

Ectopic Ureters

Ectopic ureter is the most common congenital anomaly of the equine urinary tract. The ureter inserts distal to the trigone, typically into the vagina, vestibule, or urethra rather than the bladder. Fillies are more commonly diagnosed (92% of cases), likely because incontinence is easier to detect in females.

Clinical Signs

• Continuous or intermittent urinary incontinence from birth
• Urine scalding of perineum and hindlimbs
• Normal urination may also occur (especially if unilateral)
• Colts may be asymptomatic due to retrograde bladder filling

Diagnosis

• Cystoscopy: Gold standard - visualizes abnormal ureteral orifice location
• CT with contrast: For young/small horses; traces ureteral course
• IV urography: Often unsuccessful in horses due to contrast dilution

Treatment

• Unilateral ectopia: Nephrectomy (most common) or ureteroneocystostomy
• Bilateral ectopia: Ureteroneocystostomy; more challenging prognosis

Summary: Key Differentiating Features