Neoplasia of the urinary tract

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Urinary bladder with calculus

Urinary bladder with tumour

Radiograph of a bladder injected with radiographic dye. The top right of the bladder oval is obscured, because of a “filling defect:” A transitional cell carcinoma is taking up that space in the bladder, preventing the dye from “filling up” the entire space

Introduction

Although inflammatory diseases of the bladder or cystoliths are far more common causes of dysuria and stranguria, tumours of the urinary tract should be considered as a differential diagnosis for cats presenting with signs of haematuria, stranguria, dysuria and tenesmus. Tumours of the feline urinary tract may originate from tissues of epithelial, mesenchymal or haematopoietic origin. The urothelium is at risk for developing malignant transformation because mucosa is in regular contact with carcinogenic agents that have been concentrated in the urine, then retained for long periods. Chronic inflammatory disease, carcinogens, viruses, drug metabolites, and parasites have been implicated as risk factors for the development of bladder neoplasia in human beings and dogs. Specific risk factors for the development of lower urinary tract neoplasia have not been identified in cats. Lower urinary tract tumours have been reported in the bladder, urethra, prostate (in males) and vagina (females). Tumours occur more commonly in the bladder than other anatomical locations within the lower urinary tract. Unlike dogs, tumours appear to occur more commonly in the body of the bladder than in the trigone or urethra.

Pathophysiology

Urinary tract obstruction is an emergent medical condition that can result in electrolyte and acid-base disorders, in addition to accumulation of toxic metabolites. Postrenal obstructive uraemia can develop within the first 24 hrs after obstruction. Concurrent and ensuing dehydration, metabolic acidosis, hyperkalemia, hyperphosphatemia and hypercalcaemia can further destabilise the obstructed cat. Death can occur within 3-6 days of obstruction if inappropriate therapies are not administered. After resolution of obstruction, post-obstructive diuresis develops because of the inability of the distal renal tubules to modulate water and sodium balance. Micturition dysfunction can result from decreased elasticity of the bladder, neuromuscular damage in the bladder wall, and urethral spasm. In some cases, renal failure may develop as a result of increased intrarenal pressure, electrolyte abnormalities, dehydration-related renal ischaemia, and damage caused by cytokines, As in dogs, tumours located in the trigone or neck of the bladder can cause ureteral or urethral obstruction.

Clinical signs

Clinical signs of lower urinary tract neoplasia are often present for some weeks to months before progression to obstruction. Clinical signs result from the loss of volume capacity, decreased wall compliance, and functional or mechanical outflow obstruction. Because they are often indistinguishable from signs of other, more common causes of feline lower urinary tract disease, clinical signs of lower urinary tract neoplasia often are treated symptomatically, sometimes with apparent success, before the more ominous signs of obstruction is apparent. Clinical signs of lower urinary tract neoplasia include haematuria, dysuria, stranguria, pollakiuria, tenesmus, and constipation. Clinical signs of urinary tract obstruction include anorexia, vomiting, weakness, bradycardia, enlarged urinary bladder, ascites (resulting from uroperitoneum), dehydration and coma.

Differential diagnosis

Common differential diagnoses include interstitial cystitis, urolithiasis and less commonly, bacterial infections and neoplasia.

Diagnosis

Cytology of urine sediment occasionally allows identification of malignant neoplasia cells. Care should be taken not to overinterpret cytological findings of malignancy in the face of moderate to severe inflammation. Sonography is an important non-invasive method of evaluating the kidneys, ureters, urinary bladder, proximal urethra and sublumbar lymph nodes for the presence of a mass effect. Sonography also aids in the detection of hydroureter and hydronephrosis resulting from obstruction of tumours in the trigone region. In some instances, such as in pictures above, contrast radiography contrast urethrocystography or cystography may be used to identify a bladder or urethral mass.

Treatment

Palliative treatment is the mainstay of therapy in these cases, focussing on pain relief, control of inflammation and secondary infection. Surgical debulking is indicated in some cases although response is not always rewarding in the long term. Chemotherapy is a viable adjunct to palliative care in younger patients.

References

1. © August, JR (2006) Consultations in Feline Internal Medicine, Vol 5. Elsevier Saunders