Pathophysiology

Urogenital oncologic emergencies are often related to obstruction of the ureter, bladder neck, or urethra, or to hemorrhage from the tumor. Obstructive lesions can be located extramural (intraabdominal, retroperitoneal, or intrapelvic), intramural (renal, ureteral, bladder, or urethral wall), or intraluminal. Extramural obstruction is caused by tumors in various anatomical locations including prostate (adenocarcinoma), rectum or colon (adenocarcinoma), vagina (leiomyoma or fibroma), regional lymph node (lymphoma or metastasis). Intramural and intraluminal obstructions are most often caused by transitional cell carcinoma, renal tumors, and benign proliferations. Serious and life-threatening abdominal hemorrhage and hematuria is often caused by renal tumors from direct extension of the tumor into the peritoneal or renal pelvic space. Renal tumors are usually malignant in the dog and cat, metastasize in up to 50% of cases, and most commonly affect older animals. Primary renal tumors include tubular cell carcinoma, transitional cell carcinoma, fibrosarcoma, hemangiosarcoma, and nephroblastoma in the dog; and lymphoma, renal carcinoma, sarcoma, and nephroblastoma in the cat. Ureteral tumors are rare but can cause hydronephrosis.

Bladder and urethral tumors are more common than renal or ureteral tumors and are most prevalent in female dogs and male cats. Except for rhabdomyosarcoma, bladder tumors affect older animals, and the most common tumor type in dogs and cats is transitional cell carcinoma. Transitional cell carcinomas are highly invasive tumors which grow slowly often in the trigone area and bladder neck. Emergencies associated with bladder and urethral tumors are usually caused by obstruction of the urethra or ureter. These tumors eventually metastasize in 80% of dogs. Common sites include the lung, lumbar lymph nodes, kidney, prostate, and liver.

Benign diseases must also be considered in the differential diagnosis. Chronic and acute renal failure, urinary tract infections, urolithiasis, ureteral strictures, cyclophosphamide-induced cystitis, and neurologic abnormalities could cause similar signs.

Clinical Presentation and Diagnosis

Clinical signs depend on the location and size of the tumor. Renal and ureteral tumors are associated with hematuria, renal enlargement, abdominal pain, anorexia, depression, and weight loss. Physical examination may reveal a large, painful abdominal mass and the diagnosis is confirmed by abdominal radiography, ultrasonography, contrast studies (intravenous pyelogram), renal scintigraphy, CT, or MRI scans. Routine serum chemistry and urinalysis allows evaluation of kidney function. Ultrasonographic guided fine needle aspiration of the tumor facilitates early diagnosis. Dysuria, hematuria, polyuria, pollakiuria, or anuria are observed with lower urinary tract tumors. Neoplasms associated with the bladder and urethra may be palpated by abdominal and rectal examination. Other useful diagnostic procedures include abdominal radiography, ultrasonography, and contrast studies (intravenous pyelogram, double contrast cystogram, retrograde urethrogram). Malignant cells are seldom found in the urine sediment but may be obtained by catheter biopsy or percutaneous fine needle aspiration of prostate and urethra. Direct cystoscopic visualization of the tumor in the bladder or urethra is often possible in female dogs and the diagnosis is confirmed by cystoscopic biopsy.

Surgical Therapy and Aftercare

Surgical therapy depends on the site of obstruction. Unilateral nephrectomy and ureterectomy are indicated for renal tumors if the opposite kidney is functional, and if metastases are not present. Mean survival time after nephrectomy for dogs with renal tubular cell carcinoma was 7 months and for dogs with transitional cell carcinoma it was 11 months.

Surgical excision is the therapy of choice for cystic and urethral transitional cell carcinoma but is often impossible because of tumor location. Partial cystectomy may be successful in tumors not affecting the trigone. The tumor must be excised with a wide margin of normal tissue and the remainder of the bladder wall is inspected. Even after excision of more than 75% of the urinary bladder, function can eventually return to normal or near normal. A modified "cup-patch" cystoplasty can be performed in resections of more than 80% of the bladder. When the trigone is involved, reimplantation of the ureters in the remaining bladder may be necessary. Total cystectomy has been combined with urinary diversion, but postoperative complications have made these salvage procedures less beneficial. Ureterocolonic anastomosis seems to be most successful of the urinary diversion techniques. In general, survival times after surgical excision of bladder and urethral transitional cell carcinoma are limited because of recurrence or metastasis. Temporary relief can also be obtained using an indwelling urinary or prepubic, cystostomy catheter. The placement of cystostomy catheter is relatively simple and is associated with few complications and easy home management. This technique can be used in combination with adjuvant therapies or as palliation. A permanent cystostomy catheter eliminates the need for immediate euthanasia in dogs with advanced bladder and urethral cancer.

Adjuvant radiation or chemotherapy may be indicated, but has been associated with high rate of complications and tumor recurrence. Results of systemic or intravesicular administration of chemotherapy for transitional cell carcinoma have been variable. Partial response or stable disease was seen after intravenous cisplatin therapy in 9 out of 12 dogs. Also, the use of the nonsteroidal antiinflammatory drug piroxicam has been beneficial in obstructive canine transitional cell carcinoma, at least for palliation. Complications after oncologic bladder or urethral surgery include incontinence, postoperative diuresis, pollakiuria ("small bladder syndrome"), and infection. Incontinence is treated with parasympathomimetic drugs (e.g., bethanechol chloride) for partially denervated bladders, adrenergic agonists (e.g., ephedrine) for low pressure incontinence, anticholinergics (e.g., probanthine) for reflex neurogenic bladders, and sympatholytic drugs (e.g., phenoxybenzamine) for urethral spasm. Postobstructive diuresis should be appropriately compensated with intravenous fluid administration. Infection should be treated with antibiotics based on culture and sensitivity results.

Reference

1.  Kirpensteijn J, et al. Vet Clinics of North America [Small Animal] 1995; 25: 207-223