Richard A. Read, BVSc(Hons), PhD, FACVSc
This lecture deals with urogenital emergencies that fall into the categories of urinary obstruction/leakage and sepsis (prostate in males, pyometra in females).
Urinary Obstruction/Urine Leakage in Dogs
Obstruction to the flow of urine, especially if complete, causes serious metabolic disturbances and has serious consequences for both health and life. Urinary obstruction rapidly leads to urinary retention, and failure to excrete various waste products of cellular metabolism. These waste products are toxic to many cellular processes so illness and death will inevitably follow.
The causes of urine retention include:
Functional obstruction (e.g., with neurological disease)
Intramural obstruction (e.g., tumours, stricture formation)
Hernia entrapment (perineal)
The consequences of urine retention are:
Hyperkalaemia (bradycardia, arrhythmias, death)
Severe soft tissue injury if urine leaks into subcutaneous tissues
The differential diagnosis of urinary obstruction would include:
Bladder wall neoplasia
Neurological disease (UMN)
Working up the Problem
If the patient is straining without success, ask yourself:
1. Is the bladder full or empty?
2. Does the patient continue to strain after voiding successfully?
3. Does the patient exhibit pain while attempting to urinate?
4. Is their any urine flow or is a complete obstruction present?
5. Is the urine discoloured (blood/pus)?
6. Any history of trauma?
7. Any history of previous urinary tract disease or other disease?
If the Bladder is Full
Where is the bladder--normal location?
Perform a cystocentesis to relieve obstruction
Attempt to identify the location of the obstruction:
Pass a urethral catheter to assess level of any obstruction
Perform a retrograde contrast cystourethrogram (CCU)
The usual points of obstruction are bladder neck, prostate, perineal urethra, penile urethra and os penis.
Differential Diagnosis Associated with Various Locations of Urinary Obstruction
1. Bladder full and bladder neck obstruction:
a. Perineal hernia--check bladder position
b. Bladder mass--check urine, ultrasound, CCU
c. Male--prostate--FNAB, prostatic wash, CCU
d. Female--granulomatous urethritis--CCU--catheter biopsy
2. Bladder full and pelvic urethra obstruction:
a. Trauma/pelvic Fracture--history, plain radiography
b. Urethral neoplasia--check urine, ultrasound, CCU
c. Male--prostate--FNAB, prostatic wash, CCU
d. Female--granulomatous urethritis--CCU, catheter biopsy
3. Bladder full and penile urethra obstruction:
a. Trauma/os penis fracture--history, radiographs, catheter
b. Urethral calculus--urinalysis, catheter, radiographs (plain +/- contrast)
4. Bladder empty/straining unproductively due to irritation:
a. Urolithiasis--urinalysis, plain/contrast radiography, ultrasound
b. Cystitis/urethritis--urinalysis, plain/contrast radiography, ultrasound
c. Bladder/urethral neoplasia--check urine, ultrasound, contrast cystourethrogram
d. Granulomatous urethritis--contrast cystourethrogram, catheter biopsy
e. Vaginitis--history, vaginal discharge, speculum examination
f. Bladder rupture--catheter to confirm no urine flow, ultrasound, contrast cystourethrogram, abdominocentesis, fluid urea/creatinine
Functional Obstruction--The Neurological Bladder
If the bladder is full, the patient is not voluntarily voiding urine and there is no physical obstruction to urine flow (check with catheter), the most likely causes are an upper motor neuron neurological disorder (e.g., I/V disc), pain, or reflex dyssynergia.
Management of these cases can be difficult--a dog with multiple pelvic fractures may be unwilling to urinate not only due to pain, but because he/she cannot posture to urinate due to weakness as well as pain.
Upper motor neuron neurological disease results in increased urethral tone to the point where dangerously high pressures can be generated within the bladder as urine continues to accumulate. The bladder attempts to reduce the pressure by stretching but this rapidly leads to poor detrusor tone. Eventually, the bladder lumen pressure rises above that of the urethra and urine will begin to leak out, resulting in wet cage and the appearance of the animal voluntarily voiding urine. This assumption cannot be made unless the bladder is empty and the cage/bedding is wet with urine.
Emergency Workup of the Dysuric Patient
When you are presented with a very distressed patient that is constantly straining to urinate with a full bladder, the first step is to relieve the pressure in the bladder, either by passing a urethral catheter, or if this is not possible, by cystocentesis. Catheterisation provides useful diagnostic information about urethral patency and the site of any obstruction.
The owner should be carefully questioned about the recent history of pattern of urination:
Has the urine flow appeared normal?
Any straining to urinate?
Any change in frequency?
Any urethral discharge?
Any intermittent urination problems?
A thorough examination of the urinary tract should then follow. Because of their close association both anatomically and functionally, the examination will inevitably involve the reproductive tract as well.
Principles of Urethral Surgery
Urethral mucosa is tough and holds sutures well
Handle the mucosa gently and ensure epithelial surfaces are apposed
Monofilament absorbable sutures are preferred
Haemorrhage can be minimised by avoiding the cavernous tissue when suturing
Many absorbable suture materials lose strength rapidly in the presence of urine, particularly if the urine is alkaline. This is especially true of chromic catgut, which should never be used in the urinary tract for this reason. In the presence of bacterial infection in urine, sutures such as polyglactin 910 (Ethicon--Vicryl) and polyglycolic acid (Davis & Geck--Dexon) can lose their strength within 24 hours. Polydioxanone (Ethicon = PDS II) and poliglecaprone (Ethicon--Monocryl) suture materials being monofilament and absorbable appear to be the best suited for urethral surgery.
The benefits/disadvantages of placing a catheter in the urethra to support and protect the site of urethral repair have been a hotly debated point among urologic surgeons for decades. Catheters have been accused of promoting ascending infection and causing fibrosis and stricture, particularly if large sizes are used. Using a catheter to divert urine from the surgical site can probably be better achieved using a cystostomy tube.
Urethral Obstruction Associated with Prostatic Disease
Although dysuria and urine dribbling can be associated with most forms of prostatic disease, urethral obstruction is more commonly associated with prostatic neoplasia than with the other types of prostatic disease.
The most important diagnostic test for detecting prostatic disease is a thorough rectal examination. Ancillary diagnostic tests are then helpful to differentiate between the various types of prostatic disease.
Ancillary diagnostic tests include cytology of FNAB (+/- ultrasound guided, ultrasonography, histopathology of needle biopsy samples (+/- ultrasound guided), radiography--plain and contrast, urinalysis and culture, CBC, biochemistry, electrolytes and exploratory laparotomy.
Prostatic adenocarcinomas usually start as firm nodules within the gland but many are not diagnosed until they have reached a substantial size. Neoplastic prostates tend to adhere to the surrounding tissue, but this characteristic is also a feature of inflammatory prostatic disease. Metastasis occurs early, usually to the iliac, lumbar and pelvic lymph nodes, periprostatic tissue, lung and bladder. Bone metastasis is not common, in contrast to the disease in man in which bony metastases may become evident before the primary tumour has caused any clinical signs.
The primary goal in any case of dysuria is to locate the level of the obstruction. In dogs with complete obstruction to urine flow, relieving the pressure in the system is of paramount importance, followed by attention to the consequences of failure to void urine (uraemia, electrolyte and acid-base disturbances; bladder injury through stretching leading to atony).
Surgery of the urinary tract is demanding in that precise suturing and respect for the tissues are requirements for restoring a patent urethra with a functional diameter.
After care may require urinary diversion, either via a temporary or permanent procedure.