Urinary obstruction

• Cause: urolithiasis, mass, prostatic disease, pyelonephritis, proliferative urethritis, iatrogenic ligation of ureters during spay, stricture, dyssynergia.
• Signs: dysuria, stranguria, hematuria, lethargy, anorexia, signs of renal disease, abdominal pain.
• Diagnosis: signs, urinalysis, imaging.
• Treatment: catheterize, balloon dilation, stenting or surgically remove urethral obstructions; medical treatment, ureteral stents, subcutaneous ureteral bypass devices or surgery for ureteral obstruction.
• Prognosis: dependent on underlying cause:
  • Neoplasia (grave).
  • Urolithiasis, urethritis, dyssynergia, prostatic disease (good if treatment initiated promptly).

• Dysuria Dysuria investigation, hematuria Hematuria, stranguria or tenesmus for urethral obstruction.
• Abdominal pain, turbid urine, hematuria, signs of post-renal renal failure for ureteral obstruction, especially if bilateral. 

• Anuria.

• Signs associated with urinary tract rupture Bladder: trauma rupture.
• Post-renal azotemia Azotemia.

• Breed-related risk for urolithiasis: Dalmatian Dalmatian with urates, English Bulldog Bulldog with cysteine. 

• Reflex dyssynergia Dyssynergia most commonly occurs in large and giant-breed male dogs.

• Intraluminal: urolithiasis Urolithiasis; pyelonephrosis.
• Intramural:
  • Tumors of ureter Ureter: neoplasia (rare).
  • Tumors of urethra, ie TCC Urethra: neoplasia.
  • Tumors of bladder neck Bladder: neoplasia.
  • Proliferative urethritis.
  • Stricture from previous trauma/surgery.
• Extramural:
  • Abdominal tumors.
  • Trauma - ligation during ovariohysterectomy Ovariohysterectomy.
  • Uterine stump infections Pyometra.
  • Prostatic disease, eg neoplasia Prostate: neoplasia, abscess Prostate: abscessation.
• Functional: 
  • Spinal disease. 
  • Reflex dyssynergia. 

General

• Male dogs more frequently obstruct secondary to urolithiasis.
• Struvite urolithiasis and proliferative urethritis most commonly associated with infection.

• Urethral neoplasia is more common in female dogs.
• Specific breed disposition, eg Dalmatian/urate, for urolithiasis.
• Reflex dyssynergia most commonly occurs in large and giant-breed male dogs. 

• Urethral obstruction Urethra: obstruction commonly occurs in dogs as a result of urolithiasis, neoplasia or trauma.
• Acute urethral obstruction is seen most commonly in male dogs due to obstruction by calculi lodged at the base of the os penis.

• Prolonged ureteric obstruction Ureter: urolithiasis (>7 days in experimental studies) → dilation of proximal segment and hydronephrosis Hydronephrosis / hydroureter , eg correction of obstruction at 4 weeks: renal function 25% of normal.
• If obstruction is relieved within 7 days - little permanent damage in experimental studies.
• Complete urethral obstruction can result in hydroureter, hydronephrosis, and bladder rupture → azotemia, hyperkalemia, acidosis.

• Days.
• Correction of ureter obstruction within 7 days: little permanent damage.
• Complete urethral obstruction results in death in 3-5 days.

• The presenting clinical signs and pathophysiology depend on the site, degree, and duration of obstruction.
• Complete obstruction results in life threatening uremia Uremia, and may progress to rupture of the urinary tract.

• Stranguria.
• Pollakiuria.
• Hematuria.

• In severe cases the owner may report:
  • Vomiting.
  • Lethargy.
  • Anorexia.

• Urethral obstruction: large bladder - unable to express.

• May be able to palpate uroliths, masses or pelvic fractures, per rectum.
• Collapse, hypothermia, bradycardia, abdominal pain, or ventricular tachycardia secondary to hyperkalemia Hyperkalemia.

Radiography 

• Abdominal radiography Radiography: abdomen : some uroliths    may be seen on plain films.
• Neoplasia   (if normal   ).
• Prostatomegaly . 

Contrast radiography

• Excretory urography to evaluate kidneys and ureters Radiography: intravenous urography.
• Positive contrast urethography and double contrast urethography are best for evaluating lower urinary tract Radiography: double contrast cystography.

2-D Ultrasonography

• Useful to detect cystic calculi masses in the bladder Ultrasonography: bladder and urinary tract.
• To assess the prostate in small dogs.
• To evaluate hydronephrosis, hydroureter.

Computed tomography

• High definition of lesions. 
• Possibility to perform CT urography.

• The following may be present:
  • Hydronephrosis.
  • Hydroureter.
  • Secondary urinary tract infection Cystitis.
  • Bladder distension or rupture.
  • Prostatic disease.
  • A complete examination of urethra is required, may need opening along its full length through the prostate and penis in the male.
• Check for:
  • Calculi     .
  • Prostatic hyperplasia Prostate: benign hyperplasia and hypertrophy or neoplasia Prostate: neoplasia.
  • Cystitis.
  • Space occupying lesions in the pelvic cavity.
  • Perineal hernia (bladder malposition) Bladder: herniation.
  • Neoplasia      .
  • Malposition of kidneys (pelvic).
  • Iatrogenic (ligation of ureters during ovariohysterectomy).
  • Strictures.

• Anuria may also be due to intrinsic renal disease, eg acute tubular necrosis, so examine kidneys carefully and fix samples for histology.
• Chronic unilateral urinary obstruction may cause renal atrophy. Contralateral kidney may show compensatory hypertrophy.
• Secondary infection of hydronephrotic kidney causes pyonephrosis (pus-filled dilated kidney).

• Depends on the cause.
• Urinary obstruction causes:
  • Tubular atrophy.
  • Apoptosis.
  • Interstitial edema.
  • Fibrosis.
  • Dilation of proximal convoluted tubules.
• There may be inflammation if secondary infection has occurred.

• Glomeruli often persist among fibrous remains of cortex.
• Proliferative urethritis was associated with lymphocytic-plasmacytic, or neutrophilic inflammation and was frequently associated with positive fluorescence in situ hybridization (FISH) results. 

• For cause of obstruction - see etiology (intraluminal, intramural, extramural, functional).
• For dysuria/stranguria other than above:
  • Constipation.
  • Perineal hernia.
  • Inflammation/urethrospasm from prolonged or traumatic catheterization.
  • Urinary tract rupture.
  • Behavioral.

Treatment should involve

• Relief of obstruction/decompression of bladder for urethral obstruction:
  • Catheterization.
  • Cystocentesis Cystocentesis. This could be associated with risks of urinary bladder rupture. 
  • Emergency surgery, eg tube cystotomy Cystotomy Cystostomy: tube/urethrotomy Urethrotomy.
• Relief of obstruction/decompression of ureteral obstruction: 
  • Medical treatment with pain relief, muscle relaxants Muscle relaxant: overview. 
  • Emergency surgery.
• Evaluation and treatment of:
  • Metabolic acidosis Acid base imbalance.
  • Hyperkalemia.
  • Dehydration.
• Definitive diagnosis and treatment of underlying cause.

Intraluminal

• See also urolithiasis Ureter: urolithiasis.

Intramural

• See also neoplasia of ureter Ureter: neoplasia.

• After relief of the obstruction the patient should be monitored for:
  • Adequate urine production (>1 ml/kg/h).
  • PCV Hematology: packed cell volume /TS Blood biochemistry: total protein /K+ Blood biochemistry: potassium/creatinine Blood biochemistry: creatinine/BUN Blood biochemistry: urea to monitor resolution of initial metabolic derangements (patients may become hypokalemic and have a post-obstructive diuresis).
  • ECG if previous cardiac problems.

Treatment

• Chemotherapy for neoplasia.
• Antibiotics for proven urinary tract infections, pyelonephritis Kidney: pyelonephritis. May be needed for proliferative urethritis. 
• Muscle relaxants (eg prazosin Prazosin, terazosin, phenoxybenzamine Phenoxybenzamine), pain reliefs (eg opioids) for ureteral obstruction and dyssynergia. 
• Surgical or chemical castration for prostatic diseases. 
• Balloon dilation or stenting have been described for benign or malignant urethral obstruction. 
• Ureteral stenting or subcutaneous ureteral bypass devices have been used in patients with ureteral obstructions. 
• Surgery may be necessary for some causes.

Monitoring

• Monitor for recurrence uroliths (following cystotomy for uroliths). Preventive urinary diets may be recommended. 
• Monitor for subsequent stricture using excretory urography, ultrasonography, at 4 and 8 weeks (for trauma to ureter or calculi in ureter).

• Complete obstruction of the urethra usually results in death in 3-5 days without treatment.
• Ureteroliths can pass without surgical intervention.
• In experimental studies: <7 days obstruction ureter: little permanent damage.
• >7 days obstruction ureter: permanent kidney damage likely, eg 25% renal fuction after 4 weeks.
• Chronic obstruction ureter: may lead to ureteral rupture/urine leakage/retroperitonitis. See also trauma of ureter Ureter: trauma.

• Adequate urine production with resolution of uremia, electrolyte abnormalities, and underlying cause.

• Rupture of urinary tract due to aggressive catheterization or neglect of obstructed patient.
• Stricture of the ureter or urethra as previous site of trauma, surgery, calculi.
• Inability to control the cause. 
• Secondary urinary tract infection. 

Refereed papers

• Recent references from PubMed and VetMedResource.
• Caywood D D, Osbourne C A (1986) Surgical removal of canine uroliths. Vet Clin North Am Small Anim Pract 16 (2), 389-407 PubMed.
• Osbourne C A, Polzin D J (1986) Non-surgical management of canine obstructive urolithopathy. Vet Clin North Am Small Anim Pract 16 (2), 333-347 ScienceDirect.
• Ibrahim A, Musa B, Zein M (1984) Changes in urinary pH and glomerular filtration rate in partially obstructed canine kidney. J Urol 131 (1), 143-145 PubMed.

Other sources of information

• Stone E A (1992) Urologic Surgery of the Dog and Cat. Philadelphia: Lea & Febiger.