Read the German translation: Herausfordernde Fälle in Innerer Medizin 1 und 2

This session will include case discussions focusing on challenging cases in internal medicine. One specific topic which will be covered is ureteral obstruction in cats.

Introduction

Diseases of the urinary tract of cats can be localized in the renal pelvis, the ureters, the bladder, or the urethra. Bladder diseases are the most prevalent urinary tract diseases in cats. In recent years an increase of diseases of the upper urinary tract were observed, specifically diseases of the ureters. The upper urinary tract is difficult to access and therefore diseases of this part of the urinary tract are challenging in terms of diagnosis and therapy. They are often seen together with decreased kidney function.

Diseases of the ureters include congenital abnormalities like ectopic ureters, as well as acquired damage caused by trauma, inflammation and obstruction. The most common cause of ureteral obstruction is ureteroliths. However, ureters also can be obstructed when no stones are present or when the stones passed through the ureter into the bladder causing damage to the ureter. The ureters might no longer be patent because of strictures, blood clots, inflammatory debris or oedematous thickening of the ureteral mucous membrane.

Ureteroliths

The frequency of ureteroliths, often seen in conjunction with renal insufficiency, is increasing.¹ The cause for this increase is not known. Still, hypercalcemia and feeding acidified diets are discussed as possible causes. 70% of nephro- and ureteroliths in cats are composed of calcium oxalate.² Ureteroliths tend to develop in middle-aged to older cats (median 7 years). Still, even very young cats can suffer from ureteroliths. No sex predilection occurs.³

Symptoms

Symptoms are commonly unspecific and often mild. Dysuria, abdominal pain, anorexia, vomiting, and apathy may occur. Obvious signs of an acute uremia are seen when both ureters are obstructed. Even if only the ureter of one side has ureteroliths, 76% of the cats show azotemia, which indicates a decreased function of the contralateral kidney.

Associated with ureteral obstructions the so called "big kidney, small kidney" phenomenon is often seen. The average length, width and thickness of cat kidneys are 41 mm, 29 mm, and 23 mm respectively. In the ventro-dorsal projection on radiographs the kidneys measure 1.9 to 2.6 times the length of the 2. lumbar vertebra, in uncastrated cats they measure 2.1 to 3.2 times this length. Basically, differences in kidney size are seen if one kidney is small and the other normal or big or if one kidney is normal and the other big. Oftentimes the small kidney represents an end stage kidney and the size of the other kidney is increased due to compensatory increase in function. The destruction of the small kidney can be due to stones which obstructed the ureter for some time and then passed into the bladder, while leaving permanent damage in the respective kidney. This is often not recognized as long as the big kidney functions normal. As soon as the big kidney is damaged too azotemia might develop.

Diagnosis

Ureteroliths were only seen in 90% of cases when radiography and ultrasound were used in combination.³ On radiographs alone only 81% of the stones were diagnosed. Superimposition of intestines, small stones, or radiolucent stones could be an explanation for this low detection rate with radiography. Contrast computed tomography or antegrade contrast pyelography might provide better results.

In case of an acute uremia or an acute worsening of a chronic uremia it is often not obvious which kidney has more functional tissue and therefore it is not clear on which side a possible surgical intervention would make sense. This is particularly true when both kidneys have a dilated pelvis and both ureters are dilated. Measuring the glomerular filtration rate of each kidney would be ideal for these emergency cases. However, modalities like scintigraphy which are capable to measure the glomerular filtration rate of each kidney separately are not readily available in general practice.

Therapy

Preferably cats with ureteral obstructions are treated medically, until it is clear that the stone, several stones or other obstructive material do not leave the ureter and get into the bladder or back to the renal pelvis or that a possible swelling of the ureter is not decreasing. As supportive therapy infusions and analgesics are given. Spasmolytic and anti-inflammatory medications are added; however, no study has proven efficacy of such drugs in cats for this purpose. If the ureters remain not-patent surgical interventions are needed. Procedures performed in these cases are ureterotomy, partial ureterectomy, ureteroneocystostomy, ureteroureterostomy, and nephrectomy. Recently the use of ureteral stenting was described.⁴ To stabilize the patient before any intervention hemodialysis might be needed.

Prognosis

Cats which were treated medically and survived the first month had a survival rate of 66% after 12 months in one study.⁵ Perioperative complications occurred in 31% of the cats which were treated surgically. Cats which were treated surgically and survived the first month had a survival rate of 91% after 12 months. Recurrence rates for death seem to be high. Ureteroliths recurrence occurred in 40% of the cats after 2 to 88 months (median 13 months).

References

1.  Kyles, et al. In: Bonagura JD, Twedt DC, (Eds) Kirk's Current Veterinary Therapy XIV 2009; 931.

2.  Osborne, et al. Vet Clin Small Anim 2008; 39: 183.

3.  Kyles, et al. J Am Vet Med Assoc 2005; 226: 932

4.  Berent, et al. J Vet Intern Med 2009; 23: 688.

5.  Kyles, et al. J Am Vet Med Assoc. 2005; 226: 937.