Calcium oxalate urolithiasis
Calcium oxalate uroliths are commonly found in both dogs and cats. In dogs, hypercalciuria predisposes to calcium oxalate urolith formation and may occur due to excessive intestinal absorption of calcium (absorptive calciuria), impaired renal reabsorption of calcium (renal leak calciuria), or hypercalcaemia (resorptive calciuria). Calcium oxalate uroliths tend to be radiodense, often rough and round or oval in shape and are not pH sensitive.
Calcium phosphate urolithiasis
Calcium phosphate uroliths are uncommon in both dogs and cats but where they occur the most common forms are hydroxyapatite and brushite. These uroliths are very radiodense, smooth and round or faceted. With the exception of brushite, they are less soluble in alkaline urine. Conditions resulting in hypercalciuria will predispose to their formation. Calcium phosphate is more commonly found as a minor component of struvite or calcium oxalate uroliths.
Cystinuria occurs as a result of an inherited defect in cystine transport in the renal tubules. Cystinuria predisposes to cystine urolithiasis. Most cystine uroliths are relatively radiolucent, smooth and oval and are more likely to form in acid urine. They represent 1-3% of canine uroliths in the USA, but the incidence varies geographically, being higher in other parts of the world. They are relatively uncommon in cats.
A congenital anomaly involving one or both ureters. There is failure of the affected ureter to terminate in the trigone region of the bladder, opening instead into the urethra, vagina or uterus. Continuous or intermittent urinary incontinence may be seen as a result, usually in the juvenile bitch. Urinary incontinence is less commonly associated with ectopic ureters in the male because of the longer length of the urethra and stronger urethral sphincter.
Familial renal disease
Familial diseases include those that occur in related individuals with a greater frequency than chance alone would allow. Familial renal disease should be suspected whenever chronic renal failure occurs in an immature or young animal. If chronic renal failure develops before physical maturity, stunting will develop. Familial renal diseases vary in clinical signs and pathology depending on the breed:
• Glomerular basement membrane disorder: the main lesion in this condition is a thickening and splitting of the glomerular basement membrane, usually resulting in early-onset proteinuria and leading to renal failure.
• Periglomerular fibrosis: periglomerular fibrosis progresses to generalised interstitial fibrosis and results in renal failure.
• Membranoproliferative glomerulonephritis: glomerulonephritis results from the presence of immune complexes in the glomerular capillary walls, leading to glomerular damage. Glomerulonephritis may be classified histologically as membranous, proliferative or membranoproliferative. In most cases there is significant proteinuria leading to hypoalbuminaemia which, if severe, is manifest as peripheral oedema or ascites (nephrotic syndrome). The condition may progress to renal failure.
• Renal amyloidosis: see site.
• Renal dysplasia: the term renal dysplasia refers to conditions where there is disorganised development of the renal parenchyma resulting in the persistence of structures inappropriate to the stage of development, e.g. immature glomeruli.
Fanconi’s syndrome results from renal tubular dysfunction resulting in abnormal reabsorption of many solutes including glucose, amino acids and phosphate. Low blood levels of the solutes involved may result. All cases are polyuric and polydipsic. The condition may progress to acute renal failure or pyelonephritis.
See under Neurological conditions.
See under Reproductive conditions.
Polycystic kidney disease
In this disorder, large portions of the renal parenchyma are replaced by multiple cysts. Both kidneys are generally involved and in some cases cysts are found in the liver as well. Kidneys may be palpably enlarged and irregular, and the diagnosis can be confirmed by ultrasound. The condition progresses to renal failure. Renal cysts may also be seen in cases of renal dysplasia or neoplasia.
Primary renal glucosuria
See Renal glucosuria.
Reactive systemic amyloidosis
See Renal amyloidosis.
Amyloidosis results from the deposition of an insoluble fibrillar protein (amyloid) in a variety of organs, resulting in their dysfunction. Reactive systemic amyloidosis is a systemic syndrome which is familial in the Abyssinian cat and Shar Pei dog, in which amyloid deposition can be found in many organs. Amyloid deposits in the kidney lead to progressive renal dysfunction. In most cases there is glomerular involvement, resulting in moderate to severe proteinuria and sometimes nephrotic syndrome. In most breeds, renal amyloidosis is seen in older dogs; however, in the Shar Pei dog and Abyssinian cat it is seen at an earlier age.
This is a condition of bilateral and multifocal primary renal neoplasia which is seen primarily in the German Shepherd Dog. Cases present at 5-11 years of age with anorexia, weight loss and polydipsia. The renal condition is associated with generalised cutaneous nodules (nodular dermatofibrosis) and, in females, with multiple uterine leiomyomas.
Glucosuria with normal blood glucose levels is uncommon in dogs and cats. It indicates tubular dysfunction and may be seen as part of Fanconi’s syndrome, familial renal conditions or as an isolated defect with normal renal function (primary renal glucosuria).
Abnormal development of blood vessels leads to the formation of cavernous spaces filled with blood clots which appear macroscopically as red or black nodules in the kidney and sometimes in other tissues. Affected individuals present with marked haematuria.
See under Neurological conditions.
Silica uroliths are uncommon. They have a characteristic jackstone appearance, are relatively radiodense and are less soluble in acid urine. There may be a link between dietary ingredients (notably corn gluten feed and soybean hulls) and silica urolith formation. A higher prevalence in large-breed dogs may be explained by the tendency to feed dry diets containing large quantities of plant ingredients such as these.
Struvite (magnesium ammonium phosphate) urolithiasis
Struvite uroliths are relatively common in cats and dogs. They are generally radiodense, smooth, round or faceted stones. Alkaline urine and (in dogs) urinary tract infection with urease-producing bacteria favour their formation.
Unilateral renal agenesis
Congenital absence of one kidney. Often an incidental finding, but individuals are predisposed to renal failure if the remaining kidney becomes compromised.
Ammonium urate, sodium urate, calcium urate and uric acid uroliths are relatively radiolucent and usually found as multiple, small, smooth, round or oval stones of brown-green colour.
They tend to form more in acid urine and where there is concurrent infection with urease producing bacteria. Dalmatians are predisposed to the development of urate uroliths because of a reduced capacity to convert uric acid to allantoin in the liver, leading to high levels of urinary uric acid excretion. Animals with hepatic portal vascular anomalies are predisposed to ammonium urate uroliths, owing to the reduced hepatic ability to convert ammonia to urea and uric acid to allantoin. This leads to increased urinary excretion of these substances.
Prolapse of the urethral mucosa through the external urethral orifice may occur in young male dogs. Brachycephalic breeds may be predisposed.
Urethral sphincter mechanism incompetence
A weak urinary sphincter allows urine leakage, usually when the animal is relaxed and lying down. The condition is the most common cause of urinary incontinence in the adult dog and is most commonly diagnosed in neutered females of medium to large breeds. In many cases, the condition is responsive to reproductive hormone administration.
An uncommon condition in which a fistula connects the lumen of the urethra with the lumen of the large bowel. Most cases are congenital but the condition may be acquired secondary to trauma or neoplasia. Affected animals may pass urine via both the anus and the penis or vulva, and are predisposed to urinary tract infection.
The formation of stones (uroliths) anywhere within the urinary tract.