Introduction

• Uroperitoneum is presence of free urine in the peritoneal cavity.
• Cause: damage or congenital malformations of the urinary system.
• Signs: depression, abdominal pain and distension.
• Most often seen in young foals, within a week of birth, but can be seen in adult horses and generally follows damage to the urinary system that may be secondary to urolithiasis or foaling.
• Diagnosis: presence of urine in a peritoneal fluid aspirate.
• Treatment: initial stabilization of the patient, followed by surgical repair of the damaged or malformed area.
• Prognosis: guarded. In foals the survival rate is approximately 60%.

Pathogenesis

Etiology

• Most common form is seen in approximately 1% of foals, mainly Thoroughbred males, who rupture their bladders   Bladder: rupture  during the birth process due to the pressure exerted on the bladder (predisposed by long urethra) or as a consequence of urachal leakage secondary to infection of umbilical/urachal structures.
• Approximately 1% of foals with uroperitoneum have it as a result of a congenital malformation of bladder or ureters. The bladder defects are only distinguishable from the ruptured bladder foal   Bladder: rupture  at surgical intervention and are treated surgically.
• Urethral defects can be uni/bilateral and usually involve the proximal one third. Urine accumulates retroperitoneally initially.
• The disease occurs occasionally in adult horses, and is usually seen secondary to either injuries sustained at foaling, or blockage of the urethra with uroliths and consequent bladder rupture   Bladder: rupture  .

Predisposing factors

• Rupture of the bladder   Bladder: rupture  is usually along the dorsal surface where it is weakest in newborn foals.
• Malformation of the bladder or ureters causes problems in young foals.
• In adults predisposing factors are recent foaling with bladder damage, or urolithiasis.

Pathophysiology

• Damage/malformation of the ureters, bladder or urethra results in leakage of urine into the peritoneal cavity.
• This causes a chemical peritonitis, the irritant effects of the urine causing inflammation, given that the urine is sterile. If cystitis   Bladder: cystitis - bacterial  or pyelonephritis is also present a bacterial peritonitis   Abdomen: peritonitis  may result.
• Loss of urine into the peritoneum reduces the amount passed normally.
• Presence of urine in the peritoneum causes increased permeability of the peritoneal membrane, and loss of fluid and cells into the peritoneum.
• Hypovolemia and shock can result.
• Incomplete bladder/ureteral margin allows urine leakage into peritoneum.
• Chemical effect causes inflammation of peritoneum, with consequent partition of fluid into peritoneum.
• Abdominal pain and distension, with straining due to inflammation can result.
• Cardiovascular and circulatory shock can follow.
• Loss of sodium and chloride ions into peritoneum result in hyperkalemia   Blood: biochemistry - potassium  , hypochloremia   Blood: biochemistry - chloride  , hyponatremia   Hyponatremia    Blood: biochemistry - sodium  and metabolic acidosis   Acid-base imbalance  . Hypoglycemia   Hypoglycemia    Blood: biochemistry - glucose  is often common.
• Hyperkalemia may   →   cardiac arrhythmias   Heart: sinus dysrhythmia  .
• Dehydration and septicemia   Foal: neonatal septicemia syndrome  /toxemia may also occur.

Timecourse

• Disease is generally seen in foals within a week of birth. In adults, also, symptoms take from a day to a week from the original injury to come to light.

Diagnosis

Treatment

Outcomes