Urinary Tract Trauma
The kidneys are well protected by the
rib cage, vertebrae, and lumbar muscles and therefore are not easily damaged by blunt
trauma. Possible types of renal injury include avulsion of the renal artery or vein
resulting in massive blood loss or tearing of the renal pelvis or avulsion of a ureter
allowing urine to accumulate in the retroperitoneal space or abdomen. The most common
clinical sign of renal injury following blunt trauma is hematuria, either gross or
microscopic. Hematuria can lead to formation of a blood clot in the renal pelvis,
obstructing urine flow and leading to acute renal failure.
A diagnosis of renal trauma is made based upon history and
physical or laboratory evidence of hematuria, anemia if blood loss is severe, and serum
chemistries compatible with uremia (increased BUN, creatinine, phosphorus and potassium).
Contrast studies (intravenous
pyelogram = IVP) or ultrasound may be used to evaluate for the presence of urine
leakage.
The patient may need stabilization in the form of shock
therapy prior to performing diagnostics. If renal injury is severe and unilateral, a
nephrectomy may be necessary.
Trauma to the ureters is rare.
Avulsion of the ureter at the renal pelvis may occur resulting in urine leakage, first
into the retroperitoneal space, then into the peritoneal cavity.
Iatrogenic trauma to the ureter may occur during
ovariohysterectomy with accidental ligation. If the animal has normal renal function, you
may not see signs as there remains 50% renal function. If this mistake is recognized,
attempts should be made to restore patency to the ureter by removal of the ligature or by
resection and anastamosis of the ureter. Ureteral ligation results in accumulation of
urine in the kidney which will result in
hydronephrosis.
Eventually the kidney will become a shell of renal tissue surrounding a fluid filled
structure. The hydronephrotic kidney may be identified years later as an incidental
finding.
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The bladder is much more susceptible
to injury by blunt trauma than are the kidneys. The bladder may also rupture spontaneously
if the urethra is obstructed, for example by a calculus.
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Animals may still void urine
with a ruptured bladder as the ruptured site may temporarily be sealed by omentum although
most animals with a ruptured bladder are anuric. Animals with pelvic or
caudal abdominal
trauma are at greatest risk for rupture of the bladder or urethra. Both the bladder and
urethra are also at risk for injury during repair of orthopedic injuries of the pelvis.
The most common clinical signs associated with bladder rupture are
the presence of an enlarged tender abdomen and signs of postrenal uremia (depression,
vomiting, etc.). Hyperkalemia may result in life threatening cardiac arthymmias .
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Diagnosis of a ruptured bladder can be made by
abdominocentesis, positive contrast cystography or ultrasound. The fluid obtained by
abdominocentesis is a mixture of urine, blood and fluids which were drawn to the
peritoneal cavity by the osmotic effects of urine solutes. Therefore the fluid may not
look or smell like urine. If the creatinine concentration in the abdominal fluid exceeds
the concentration in blood, the fluid is likely urine. Creatinine is a fairly small
molecule so it will equilibrate across the two fluid compartments (blood and abdominal
fluids) so the presence of a creatinine concentration in the abdominal fluid equal to that
of blood does not rule out that the fluid is urine.
The patient must be stabilized with fluid therapy and
supportive measures to temporarily
reverse the toxic
effects of hyperkalemia on the myocardium prior to surgical repair of the bladder.
The urethra can be ruptured by
abdominal trauma, bite wounds, urethral obstruction with calculi or improper
catheterization. Unstable pelvic fractures may lacerate the urethra. Rupture of the pelvic
urethra results in urine leakage into the abdomen while a rupture of the distal urethra
results in extravasation of urine into soft tissues in the perineal region. Urethral
rupture can be confirmed with a positive contrast urethrogram. The urinary catheter must
be carefully placed to avoid further tearing of the urethra. Small tears may heal without
surgical intervention if a urinary catheter can be placed beyond the tear to act as a
stent around which the urethra will heal. If the urethral tear is not repairable a
urethrostomy must be performed proximal to the tear.
Last Edited: Jul 26, 2007 12:58 PM
