- Structural Anomalies of the Kidney
- RENAL AGENESIS
- RENAL HYPOPLASIA
- RENAL DYSPLASIA AND APLASIA
- TUBULOINTERSTITIAL NEPHROPATHIES
- POLYCYSTIC RENAL DISEASE
- RENAL ECTOPIA AND FUSION
- DUPLEX AND SUPERNUMERARY KIDNEYS
- PRIMARY RENAL NEOPLASMS
- Functional Anomalies of the Kidney
Structural Anomalies of the Kidney
Renal agenesis is the complete absence of one or both kidneys. Bilateral renal agenesis is fatal and is a cause of early death in puppies and kittens (). Unilateral renal agenesis is more frequendy observed in puppies and kittens than is bilateral agenesis (). Unilateral renal agenesis may affect either kidney and is usually accompanied by ipsilateral ureteral agenesis. The etiopathogenesis of renal agenesis in dogs and cats is uncertain. A familial predisposition for renal agenesis in beagles, Shetland sheepdogs, and Doberman pinschers supports a genetic basis for the anomaly (Table 17-1). Unilateral renal agenesis may remain clinically silent, provided the contralateral kidney undergoes sufficient compensatory change to maintain normal hemostasis. Clinical findings may include an inability to palpate both kidneys or to detect a kidney by ultrasonography or contrast urography. Because of close associations in the development of the urogenital system, findings of abnormal or absent vas deferens, epididymal tails, or uterine horns at the time of castration or ovariohysterectomy should arouse suspicion of concurrent unilateral renal agenesis. Because unilateral renal agenesis is compatible with normal life, specific therapy is not indicated unless reduced renal function exists.
Hypoplastic kidneys appear as miniature replicas of normal kidneys composed of reduced numbers of histologically normal nephrons (). Renal hypoplasia occurs sporadically in puppies and kittens (). Embryonic pathogenic mechanisms resulting in renal hypoplasia may involve inadequate metanephric blastema, insufficient branching of the ureteric bud, reduced nephron induction, or failure of postnatal renal tubular growth (). Clinical signs, therapy, and prognosis depend on the extent of involvement; unilateral disease may be clinically silent, whereas severe bilateral disease is typically associated with renal failure.
RENAL DYSPLASIA AND APLASIA
Renal dysplasia refers to disorganized parenchy-mal development characterized by segmental or focal areas of immature or anomalous structures in an otherwise normal kidney (). Renal aplasia represents a more severe generalized form of dysplasia that affects the entire kidney. Renal dysplasia has been observed in male and female puppies, but rarely in kittens (see Table Congenital Renal Diseases of Dogs). Renal dysplasia is a familial disorder in the Lhasa apso, Shih Tzu, soft-coated wheaten terrier, and standard poodle (see Table Congenital Renal Diseases of Dogs). In addition a hereditary basis is strongly suspected in keeshonds, chow chows, and miniature schnauzers (see Table Congenital Renal Diseases of Dogs). Renal dysplasia has been associated with in utero inoculation of kitten fetuses with panleukopenia virus and in puppies with canine herpesvirus ().
Puppies with renal dysplasia may appear clinically normal for extended periods before development of signs of chronic renal failure (CRF). The rate at which renal dysplasia progresses to overt renal failure depends on the severity of initial renal lesions and factors resulting in progressive loss of renal functional mass (). Age of onset of clinical signs is variable, ranging from 4 weeks to more than 5 years; however, most cases of chronic renal failure are recognized in puppies younger than 2 years (). Early signs of chronic renal failure are often subtle and may include lethargy, selective appetite, poor haircoat, variable weight loss, nocturia, and mild to moderate polyuria and polydipsia (). Severe dysplasias are associated with signs of advanced chronic renal failure and uremia (anorexia, depression, vomiting, diarrhea, dehydration, halitosis, oral ulceration, pale mucous membranes, and severe weight loss). Abdominal palpation may reveal small, irregularly shaped kidneys. Symmetric enlargement of the maxilla and mandible, bone pain, soft pliable mandibles (“rubber jaw”), and pathologic fractures are occasionally observed in young dogs with renal dysplasia and are indicative of severe renal osteodys trophy.
Table Congenital Renal Diseases of Dogs
|Breed Predilection||Disorder||Inheritance||Sex Predilection||Typical Age At Diagnosis||Signs And Symptoms|
|Abyssinian cat||Amyloidosis||Unknown||None||1-5 y||Proteinuria, CRF|
|Basenji||Fanconi-like syndrome||Unknown||None||1-7 y||PU, glucosuria, ARF|
|Basset hound||Cystinuria||Unknown||M||Incidental||Cystine crystalluria, uroliths|
|Polycystic kidneys||Auto recessive||None||<2 y||Renomegaly, CRF|
|Amyloidosis||Unknown||None||5-11 y||Proteinuria, CRF|
|Glomerulopathy||Unknown||None||<9 y||Proteinuria, CRF|
|Bedlington terrier||Dysplasia||Unknown||None||<2 y||CRF|
|Bernese mountain dog||Glomerulopathy||Auto recessive||F>M||2-7 y||Proteinuria, CRF, NS|
|Cystinuria||Unknown||M||Incidental||Cystine crystalluria, uroliths|
|Hyperuricuria||Unknown||M||Incidental||Urate crystalluria, uroliths|
|Glomerulopathy||Auto dominant||None||1-8 y||Proteinuria, CRF|
|Polycystic kidneys||Auto dominant||None||<2 y||Renomegaly, CRF|
|Cairn terrier||Polycystic kidneys||Auto recessive||None||<1 y||Renomegaly, CRF|
|Cocker spaniel||Glomerulopathy*||Unknown||None||<2 y||Proteinuria, CRF|
|Cystinuria||Unknown||M||Incidental||Cystine crystalluria, uroliths|
|Xanthinuria||Unknown||None||Incidental||Xanthine crystalluria, uroliths|
|Hyperuricuria||Auto recessive||None||Incidental||Urate crystalluria, uroliths|
|Glomerulopathy||Unknown||None||<6 y||Proteinuria, CRF, NS|
|English cocker spaniel||Glomerulopathy||Auto recessive||None||<2 y||Proteinuria, CRF|
|English foxhound||Amyloidosis||Unknown||None||<9 y||Proteinuria, CRF|
|German shepherd||Cystadenocarcinomas||Auto dominant*||None||5-11 y||Renomegaly, hematuria, CRF|
|Irish terrier||Cystinuria||Auto recessive||M||Incidental||Cystine crystalluria, uroliths|
|Lhasa apso||Dysplasia||Unknown||None||<5 y||CRF|
|Miniature schnauzer||Dysplasia||Unknown||None||<3 y||CRF|
|Newfoundland||Cystinuria||Auto recessive||None||Incidental||Cystine crystalluria, uroliths|
|Norwegian elkhound||Tubulointerstitial nephropathy||Unknown||None||<5 y||CRF|
|Oriental short-haired cat||Amyloidosis||Unknown||None||<5 y||CRF|
|Rottweiler||Glomerulopathy||Unknown||None||<1 y||Proteinuria, CRF|
|Samoyed||Glomerulopathy||X-linked dominant||M > F||<1 y||Proteinuria, CRF|
|Shar-pei||Amyloidosis||Unknown||None||1-6 y||Proteinuria, chronic renal failure NS|
|Shetland sheepdog||Unilateral agenesis||Unknown||None||Incidental||Asymptomatic|
|Shih Tzu||Dysplasia||Auto recessive||None||<9 y||CRF|
|Soft-coated wheaten terrier||Dysplasia||Auto recessive||None||<3 y||CRF|
|Glomerulopathy||Unknown||None||2-11 y||Proteinuria, CRF, NS|
|Standard poodle||Dysplasia||Unknown||None||<1 y||CRF|
|Tibetan spaniel||Hyperoxaluria||Unknown||None||<1 y||ARF|
|Welsh corgi||Telangiectasia||Unknown||None||2-8 y||Hematuria, renal pain|
|West Highland white terrier||Polycystic kidneys||Auto recessive*||None||<1 y||Renomegaly, CRF|
|Nephroblastoma||Unknown||None||<11 y||Renomegaly, hematuria|
|Nephrogenic diabetes insipidus||Unknown||None||<2 y||PU|
ARF = acute renal failure; auto = autosomal; chronic renal failure = chronic renal failure; F = female; M = male; NR = not reported; NS = nephrotic syndrome; PU = polyuria.
** No specific breed association has been identified.
Laboratory findings with renal dysplasia reflect changes associated with chronic renal failure and typically include azotemia, hyperphosphatemia, metabolic acidosis, and normocytic normochromic nonregenerative anemia (Polzin and Osborne, 1995b). Serum calcium concentrations may be decreased, normal, or increased. Typically, serum calcium concentrations are normal to decreased in animals with CRF; however, some puppies develop hypercalcemia (DiBartola et al, 1983). Urinalysis usually reveals an inappropriately low urine specific gravity, an inactive urine sediment, and occasional mild to moderate pro-teinuria. A diagnosis of renal dysplasia is based on breed and clinical and laboratory findings (Table Problem-Specific Database for Renal Failure in Immature Dogs). A definitive diagnosis of renal dys-plasia depends on identification of primary dysplastic lesions by microscopic evaluation of renal tissues obtained by biopsy or necropsy. Primary lesions suggestive of renal dysplasia include (1) fetal or immature glomeruli and/or tubules, (2) persistent mesenchyme, (3) persistent metanephric ducts, (4) atypical tubular epithelium, and (5) dysontogenic metaplasia ().
Table Problem-Specific Database for Renal Failure in Immature Dogs
- Medical history
- Note age, sex, and breed
- Note duration of signs
- Note potential exposure to nephrotoxins, infectious agents, or drugs
- Note previous illness, injury, surgery, or anesthetic episode
- Note concurrent illness in siblings
- Physical examination
- Determine hydration status
- Examine oral cavity for liberations, loose or missing teeth, enlargement of maxillary tissues, and pallor of mucous membranes
- Palpate kidneys for number and changes in size, shape, position, consistency, and pain
- Palpate urinary bladder for size, shape, consistency, and position
- Palpate urethra per rectum
III. Complete urinalysis
IV Quantitative urine culture (preferably collected by cystocentesis)
- Complete blood count
- Serum biochemistries
- Urea nitrogen and creatinine concentration
- Sodium, potassium, and chloride concentrations
- Calcium and phosphorus concentrations
- Bicarbonate or total carbon dioxide concentrations
- Total protein and albumin concentrations
VII. Survey abdominal radiographs
- Kidneys — size, shape, location, number
- Uroliths — location, number, character
- Urinary bladders — size, shape, location
VIII. Fundic examination
- Renal ultrasonography
- Excretory urography
- Blood pressure determination
- Serum parathormone and ionized calcium concentrations
- Renal biopsy
Renal dysplasia is an irreversible and often progressive disorder for which there is no specific therapy. Clinical and pathologic consequences of renal failure may, however, be minimized by supportive and symptomatic therapies designed to correct fluid, electrolytes, acid-base, endocrine, and nutritional imbalances. Therapeutic strategies for the management of chronic renal failure include the following: (1) ameliorate clinical signs of uremia; (2) correct fluid, electrolyte, and acid-base abnormalities; (3) minimize endocrine and hematologic disturbances; (4) provide adequate nutritional support; (5) modify progression of renal dysfunction; and (6) avoid conditions that exacerbate or promote progressive renal dysfunction. Recommendations regarding therapy should be individualized for each puppy ().
Because chronic renal failure associated with renal dysplasia is often progressive, serial clinical and laboratory evaluations are helpful for effective long-term management. Because moderate protein restriction is of benefit to uremic dogs and cats and may have potential long-term benefits with respect to renal hemodynamics, proteinuria, renal growth, and phosphate retention, it is logical to recommend feeding reduced-protein diets (). Optimal daily protein requirements for puppies and kittens with chronic renal failure are not known. Therefore, serial determinations of serum albumin concentration and body weight should be performed to monitor for malnutrition and hypoalbuminemia.
Hyperphosphatemia is a major factor promoting development of renal secondary hyperparathyroidism and progressive decline of renal function in dogs and cats with chronic renal failure (). A goal of medical therapy is to normalize serum phosphorus concentrations (). In early stages of CRF, hyperphosphatemia may be controlled by dietary phosphorus restriction alone. In advanced CRF, control of serum phosphorus concentrations may require administration of oral intestinal phosphate-binding agents. Serum phosphorus concentrations should be monitored regularly to evaluate therapeutic efficacy of dietary phosphate restriction and intestinal phosphate binders.
Congenital renal diseases affecting predominantly the glomerulus have been described in young Bernese mountain dogs, English cocker spaniels, Samoyeds, Doberman pinschers, bull terriers, cocker spaniels, and Rottweilers. Proteinuria is the hallmark of glomerular disease. Although severe proteinuria may be associated with the nephrotic syndrome (i.e., proteinuria, hypoalbuminemia, hypercholesterolemia, and edema), most puppies and kittens with congenital glomerulopathies develop signs of advanced CRF. As functional and morphologic abnormalities of the glomeruli induce secondary changes in renal tubules, interstitium, and blood vessels, clinical manifestations of generalized renal dysfunction and renal failure supervene ().
Samoyed hereditary glomerulopatby is a genetic disorder of Samoyeds resulting from inheritance of an abnormal X-linked dominant gene (). The inherited defect results in alteration of type IV collagen molecules that are major components of the glomerular capillary basement membrane (). Hereditary glomerulopathy of Samoyeds affects both male and female dogs; however, males are affected more frequently (). Affected male dogs develop persistent proteinuria and, occasionally, microscopic hematuria as early as 2 to 4 months of age. Most affected male dogs develop signs of chronic renal failure and uremia; death due to end-stage chronic renal failure occurs between 8 and 16 months of age. Affected female dogs have milder clinical signs and are less likely to progress to overt renal failure (). Affected females may have mild proteinuria that persists for several years before clinical signs of chronic renal failure develop in middle or older age. In affected males, kidneys are reduced in size. Microscopic lesions are characterized by primary membranoproliferative glomerulonephri-tis progressing to glomerulosclerosis. Ultrastructurally, multilaminar splitting of the lamina densa of glomerular capillary basement membranes is evident as early as 1 month of age and often precedes development of microscopic abnormalities ().
Bull terrier hereditary nephritis is a genetic disorder of bull terriers characterized by ultra-structural abnormalities of the glomerular capillary basement membrane similar to those observed in Samoyed hereditary glomerulopathy (). Unlike the disorder in Samoyeds, hereditary nephritis of bull terriers appears to be inherited as an autosomal dominant gene (). In addition, both male and female bull terriers appear to be affected with equal frequency and have similar clinical features (). Affected terriers usually die from chronic renal failure between 10 months and 9 years of age. Kidneys are usually small with finely irregular cortical surfaces. Lesions observed by microscopy include reduced numbers of glomeruli, glomerular tuft atrophy, tubular dilation, corticomedullary fibrosis, mineralization of Bowman’s capsule and renal tubules, and variable interstitial mononuclear cell infiltration. Extensive thickening and splitting of the basement membranes of glomerular capillaries, Bowman’s capsule, and renal tubules are observed by electronic microscopy.
Doberman pinscher familial glomerulonephritis has been described in related Doberman pinschers (). Clinical signs of chronic renal failure are first observed between 6 weeks and 8 years of age. No sex predilection is apparent; however, males appear to be affected earlier (average age 20 months) than females (average age 31 months) (). Urinalyses typically reveal persistent marked proteinuria and variable glucosuria. Most, but not all, animals affected with familial glomerulonephritis develop clinical signs and laboratory abnormalities consistent with CRF. Dogs with advanced disease often die or are euthanized between 6 months and 9 years of age. Five of 20 female Dobermans with hereditary nephritis had concurrent unilateral renal and ureteral aplasia (). Kidneys are usually normal or slightly small in size and have an irregularly pitted surface (). Microscopic lesions are suggestive of a primary membranoproliferative glomerulonephritis and accompanied by variable degrees of tubulointerstitial disease (). Renal lesions include glomerular sclerosis, cystic glomerular atrophy, atrophy and dilatation of renal tubules, interstitial mononuclear cell infiltration, fibrosis, and mineralization and hyperplasia of collecting duct epithelium. Glomerular ultrastructural lesions are characterized by multifocal irregular thickening of the glomerular basement membrane or diffuse thickening of the glomerular basement membrane zone (). The pathogenic mechanisms involved in Doberman familial nephritis and mode of inheritance are unknown. Variability in clinical course and rate of progression may be indicative of different degrees of gene expression or, conversely, factors that potentiate heritable renal defects. Immunofluorescent studies have identified immunoglobulins and complement in glomeruli of some affected dogs. These findings appear, however, to be inconsistent features of Doberman familial glomerulonephritis.
Familial nephropathy of English cocker spaniels was first described as bilateral renal cortical hyperplasia (). Subsequent investigations, however, suggest that familial nephropathy of English cocker spaniels may be considered a primary glomerulopathy (). The disorder appears to be transmitted as an autosomal recessive trait (). Clinical signs of chronic renal failure and uremia typically develop between 6 months to 2 years of age. There appears to be no sex predilection. Urinalyses consistently reveal moderate to severe proteinuria and occasional glucosuria and hematuria. Kidneys are usually normal to small in size with a mild to moderate decrease in cortical thickness (). Microscopic findings in more advanced cases include mesangial thickening, glomerular and periglomerular fibrosis, glomerular obsolescence, diffuse interstitial fibrosis, mild to moderate interstitial mononuclear cell infiltrates, tubular dilation, and mineralization of tubular basement membranes. Ultrastructural lesions are characterized by extensive thickening, multilaminar splitting, and fragmentation of the glomerular basement membrane ().
Rottweiler atrophic glomerulopathy was described in four related Rottweilers and appears to be distinct from other canine hereditary glomerulopathies (). Affected dogs develop clinical signs of chronic renal failure and uremia between 6 months and 1 year of age. Both male and female dogs are affected. Urinalysis typically reveals isosthenuria and moderate to severe proteinuria. Kidneys are usually moderately enlarged. Microscopic lesions are characterized by severe, diffuse global, atrophic membranous glomerulopathy with secondary degenerative changes. The familial nature of this disorder is suggestive of a genetic disorder; however, confirmation of this hypothesis requires further investigation.
A diagnosis of familial glomerulopathy is based on breed, age of onset of clinical signs, and laboratory abnormalities. Despite the presence of moderate to severe proteinuria, hypoal-buminemia and clinical signs consistent with the nephrotic syndrome are uncommonly observed in puppies with familial glomerular disease. A definitive diagnosis is based on microscopic evaluation of renal tissues obtained by biopsy or necropsy. The irreversible nature of familial glomerulopathies precludes specific therapy; however, supportive or symptomatic therapy may improve the quality of life and minimize progression of renal dysfunction. Results of studies in young Samoyed dogs with hereditary nephritis suggest that dietary modification may be of benefit to puppies with some types of familial glomerulopathy (). Affected puppies are to be fed a modified diet restricted in protein (14.8% dry matter basis), phosphorus (0.028% dry matter basis), and sodium (0.23% dry matter basis). Although dietary modification did not prevent development of terminal renal failure, it did appear to diminish the severity of glomerular lesions in affected males and carrier females and prolongs survival in affected male dogs.
A noninflammatory tubulointerstitial nephropathy has been identified in related Norwegian elkhounds (). This nephropathy affects both male and female dogs and is characterized by renal failure that varies in severity and rate of progression. The pathologic mechanisms responsible for familial renal disease in Norwegian elkhounds are unknown. Results of histologic, electron microscopic, and immuno-fluorescent studies do not provide evidence of glomerular, vascular, or immune-mediated renal disease (). Based on a strong familial tendency, genetic factors are suspected; however, the mode of inheritance is unknown. Azotemia may be detected in affected puppies as early as 3 months of age; however, some affected dogs may remain nonazotemic for extended periods (). In severely affected dogs, clinical signs and laboratory abnormalities are consistent with chronic renal failure and uremia. Urinalyses typically reveal impaired concentrating ability and occasional glucosuria and proteinuria. Microscopic renal lesions are not observed in affected puppies younger than 25 days (). In advanced disease, kidneys are small, white, and firm, with thin cortices and radial streaks of fibrous connective tissue. Periglomerular fibrosis and parietal epithelial cell hyperplasia and hypertrophy were consistent early morphologic lesions observed by microscopy. As the disease progresses, severe corticomedullary interstitial fibrosis becomes evident. Although no specific treatment will reverse the nephropathy, puppies with advanced disease may benefit from supportive and symptomatic therapy.
POLYCYSTIC RENAL DISEASE
Polycystic renal disease has been described in several breeds of puppies and kittens (). Polycystic renal disease is characterized by formation of multiple, variable-sized cysts throughout the renal medulla and cortex (). Affected kidneys are enlarged and lobulated and contain multiple fluidfilled epithelial lined cysts ranging in size from 0.5 mm to several centimeters in diameter. Etio-pathologic mechanisms resulting in renal cyst formation are unknown. A strong familial tendency in bull terriers, West Highland white terriers, Cairn terriers, beagles, Persian cats, and domestic long-haired cats suggests a genetic basis for polycystic disease in these species (). Polycystic renal disease in West Highland white terriers, Cairn terriers, and domestic longhaired cats is often associated with concurrent formation of hepatic biliary cysts (). Polycystic renal disease may cause progressive irreversible renal failure as a result of cyst enlargement and compression of adjacent renal parenchyma. Animals often develop abdominal enlargement, renomegaly, and clinical signs and laboratory abnormalities consistent with chronic renal failure and uremia. Radiography, ul-trasonography, and/or exploratory celiotomy and renal biopsy may help differentiate polycystic renal disease from other causes of abdominal mass lesions (i.e., renal ectopia, nonrenal neoplasms, foreign bodies, and pregnancy; Table Table Problem-Specific Database for Abdominal Distention in Immature Dogs). Symptomatic and supportive therapy may be of benefit to animals with renal failure.
Table Problem-Specific Database for Abdominal Distention in Immature Dogs
- Medical history
- Note age, sex, and breed
- Note duration and/or changes in degree of abdominal distention
- Note changes in micturition and/or defecation
- Physical examination
- Auscultate heart and lungs for evidence of heart murmurs, pulmonary edema, or pleural effusions
- Identify peritoneal fluid
- Characterize position, size, shape, consistency, and attachments of abdominal masses
- Palpate liver, spleen, kidneys, urinary bladder, intestinal tract, and genital tract for changes in size, shape, position, and consistency
- Identify and localize abdominal pain
III. Laboratory evaluation
- Complete urinalysis
- Serum chemistry profile
- Complete blood count
- Survey abdominal radiography V Abdominal ultrasonography
- Biopsy — aspiration, punch, or surgical
- Localizing contrast radiographic or ultrasonographic procedures
- Exploratory celiotomy
Renal amyloidosis is characterized by extracellular deposition of amyloid in glomerular capillary walls, glomerular mesangium, and medullary interstitium (). Renal amyloidosis is usually observed in older unrelated dogs; however, familial renal amyloidosis occurs in young related Abyssinian, Oriental short-haired, and Siamese cats and in beagle and Chinese shar-pei dogs (). The condition is usually recognized at 1 to 6 years of age at which time clinical signs and laboratory abnormalities consistent with chronic renal failure and uremia develop. Affected Chinese shar-pei dogs may have a history of intermittent pyrexia and/or swelling of the tibiotarsal joints (so-called “swollen hock disease”). Unlike older animals with nonfamilial renal amyloidosis, severe proteinuria is an inconsistent clinical feature of familial renal amyloidosis in Abyssinian cats and Chinese shar-pei dogs. This disparity most likely reflects differences in the intrarenal location of amyloid deposits. The medullary interstitium is the primary site of amyloid deposition in these breeds. Diagnosis of familial renal amyloidosis is based on breed, clinical signs and laboratory findings consistent with CRF, and demonstration of renal amyloid deposits by microscopy. No therapy is capable of slowing or eliminating renal amyloid deposition. Because renal amyloidosis often results in progressive nephron destruction and deterioration of renal function, symptomatic and supportive therapy may be of benefit.
RENAL ECTOPIA AND FUSION
Renal ectopia (with or without fusion) describes congenital malposition of one or both kidneys. Renal ectopia occurs when the mature kidney fails to reach its normal location or orientation within the abdomen (). Renal fusion represents the congenital union of normally lateralized kidneys. Fused kidneys may assume a variety of shapes; horseshoe kidneys are symmetrically fused along the medial border of either pole, resulting in a shape resembling that of a horseshoe. Not all cases of renal ectopia involve fusion. The etiopathogenesis of renal ectopia and the relationship of fusion to ectopic kidneys are not understood. Because renal ectopia and fusion do not directly result in damage to renal parenchyma, affected dogs and cats may appear clinically normal. Radiography, ul-trasonography, or exploratory celiotomy may be of value in differentiating renal ectopia from other abdominal masses (see Table Problem-Specific Database for Abdominal Distention in Immature Dogs).
DUPLEX AND SUPERNUMERARY KIDNEYS
The presence of one or more accessory kidneys (supernumerary kidneys) or the presence of an enlarged kidney with two distinct pelves and ureters (duplex kidneys) appear to be uncommon in puppies and has not been reported in kittens (). Most renal and ureteral duplications are asymptomatic; however, if pyelonephritis selectively affects a supernumerary kidney or a portion of the duplex kidney, surgical resection of the diseased moiety is recommended.
PRIMARY RENAL NEOPLASMS
Primary tumors of the kidneys are usually considered disorders of older animals; however, several renal malignancies, including nephroblastoma, lymphoma, carcinoma, and undif-ferentiated sarcoma, have been described in puppies and kittens (). Nephroblastomas (embryonal nephroma, Wilms’ tumor, congenital mixed tumor) occur in puppies younger than 6 months. Nephroblastomas are believed to be congenital tumors arising from the pluripotent metanephric blastema. Nephroblastomas vary markedly in size and usually affect a single kidney; bilateral involvement is rare (). Invasion and compression of adjacent renal parenchyma progressively destroy the affected kidney. Tumors may penetrate the renal capsule and invade local tissue or metastasize to lungs, liver, mesentery, lymph nodes, and bone. Clinical signs associated with nephroblastomas vary with location, size, and duration of the neoplasm.
Nephroblastomas typically are recognized because of signs of persistent or intermittent he-maturia and/or abdominal distention associated with a palpable mass. A diagnosis of primary renal neoplasia is based on physical examination and radiographic and ultrasonic findings (see Table Problem-Specific Database for Abdominal Distention in Immature Dogs). Definitive diagnosis requires microscopic identification of neoplastic cells in tissue samples obtained by biopsy or at the time of necropsy. Therapy has rarely been attempted for dogs with nephroblastoma, presumably due to widespread metastatic disease at the time of diagnosis. Nephrectomy and ureterectomy are recommended for animals with unilateral disease, adequate renal function in the contralateral kidney, and absence of identifiable metastatic disease (). The therapeutic efficacy of adjunctive radiation or chemotherapy in dogs with primary renal neoplasia is unknown. A dog with unilateral nephroblastoma and distant metastases, however, survived over 15 months after treatment with combination therapy utilizing unilateral nephrectomy, local radiation, and periodic administration of actinomycin D ().
Functional Anomalies of the Kidney
Generalized renal tubular dysfunction associated with impaired renal tubular resorption of amino acids, glucose, phosphate, sodium, potassium, and uric acid had been described in basenjis, Norwegian elkhounds, schnauzers, and Shetland sheepdogs (Table Congenital Renal Diseases of Dogs). Fanconi’s syndrome in the basenji dog is familial and is strongly suggestive of a hereditary defect; however, the mode of inheritance is unknown (). Gentamicin-induced acquired Fanconi’s syndrome has been reported in a dog (). The syndrome has not been reported in cats. Clinical signs develop between 1 and 7 years of age in most affected dogs and depend on the severity of renal tubular dysfunction and concomitant renal failure (). Urinalyses typically reveal glucosuria, mild pro-teinuria, and urine specific gravity values of 1.005 to 1.018. Results of serum biochemistries and hemograms are usually normal. Some affected dogs may rapidly develop severe renal failure. Diagnosis of Fanconi’s syndrome is based on breed, clinical signs of polyuria and polydipsia, and laboratory abnormalities of low urine specific gravity, normoglycemic glucosuria, aminoaciduria, nonanion gap metabolic acidosis, and hypokalemia (). Treatment should be individualized for each dog and depends on specific cause, severity of serum biochemical abnormalities, and presence of overt renal failure.
PRIMARY RENAL GLUCOSURIA
Primary renal glucosuria is an isolated hereditary defect in proximal renal tubular resorption of glucose resulting in persistent glucosuria without concurrent hyperglycemia. Primary renal glucosuria has been reported in Scottish terriers, Norwegian elkhounds, and mixed-breed dogs (Table Congenital Renal Diseases of Dogs). Primary renal glucosuria in Norwegian elkhounds appears to be familial; however, the mode of inheritance is unknown. Dogs with primary renal glucosuria are clinically asymptomatic. Laboratory findings include low urine specific gravity and persistent glucosuria in the absence of hyperglycemia. Primary renal glucosuria must be differentiated from other causes of glucosuria (i.e., diabetes mellitus, administration of dextrose-containing fluids, familial nephropathies, Fanconi’s syndrome, acute tubular necrosis, and transient glucosuria due to physiologic stress hyperglycemia).
Excessive urinary excretion of the amino acid cystine results from a heritable defect in renal tubular transport of cystine and other dibasic amino acids. Cystinuria has been observed in over 60 breeds of dogs and occasionally in cats (). The disorder predominantly affects male dogs, and analyses of pedigrees of Newfoundlands and Irish and Scottish terriers suggest a recessive mode of inheritance (). Cystinuric puppies and kittens have no detectable abnormalities associated with amino acid loss with the exception of formation of cystine uroliths. Although cystinuria represents a risk factor for development of urolithiasis, cystine uroliths are uncommon in puppies and kittens (). Observation of cystine crystals in urine sediment is expected with this disorder ().
Hyperuricuria in Dalmatian dogs is transmitted by a recessive nonsex-linked mode of inheritance (). Etiopathogenic factors responsible for hyperuricuria involve impaired hepatic conversion of uric acid to allantoin by the enzyme uricase and enhanced renal tubular secretion of uric acid (). Although hyperuricuria predisposes affected dogs to urolithiasis, urate uroliths are uncommon in Dalmatian puppies (). A high prevalence of ammonium urate uroliths has been observed in puppies with portal vascular anomalies (). Hyperuricuria may be detected by identification of characteristic uric acid, sodium, or ammonium urate (ammonium biurate) crystals in urine sediment.
Congenital xanthinuria is an uncommon metabolic disorder of puppies and kittens characterized by a deficiency of xanthine oxidase, the hepatic enzyme that catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid. As a consequence, abnormal quantities of xanthine are excreted in the urine as a major end product of purine metabolism. Because xanthine is the least soluble urine purine metabolite, xanthinuria represents a risk factor for xanthine urolithiasis. Congenital xanthinuria and xanthine urolithiasis have been observed in dachshunds and mixed-breed cats (). Because xanthine crystalluria cannot be reliably distinguished from urate crystalluria by routine microscopic urine sediment examination, a diagnosis of xanthinuria is based on detection of xanthine in uroliths analyzed by infrared spectroscopy or x-ray diffraction. Formation of xanthine uroliths in xanthinuric dogs and cats may be minimized by consumption of low-purine diets, alkalization of urine, and eradication or control of urinary tract infections.
Primary hyperoxaluria is an inborn error of metabolism resulting in excessive oxalate production and increased urinary oxalate excretion. Hereditary primary hyperoxaluria has been recognized in domestic short-haired cats and Tibetan spaniels (see Table Congenital Renal Diseases of Dogs). The predominant clinical manifestation of primary hyperoxaluria in puppies and kittens is acute renal failure caused by deposition of calcium oxalate crystals in renal tubules. Affected puppies and kittens usually develop clinical signs of acute renal failure and uremia between 7 weeks and 1 year of age. Renal lesions observed by microscopy include interstitial fibrosis and dilated necrotic proximal tubules containing rosettes of birefringent calcium oxalate crystals. Specific therapy for management of primary hyperoxaluria has not been identified.
NEPHROGENIC DIABETES INSIPIDUS
Congenital nephrogenic diabetes insipidus has been described in puppies and is characterized by severe polyuria and polydipsia (5 to 10 times normal urine volume), nocturia, and poor growth. Urine specific gravity values typically range from 1.002 to 1.004. Diagnosis of congenital nephrogenic diabetes insipidus is based on a history of persistent polyuria and polydipsia, hyposthenuric urine, and lack of response to water deprivation, partial water deprivation, hypotonic saline infusion, and antidiuretic hormone administration. Therapy for congenital nephrogenic diabetes insipidus is limited to strategies designed to reduce the severity of the polyuria and polydipsia. Use of salt-restricted diets and the diuretic chlorothiazide have been reported to reduce the magnitude of polyuria by 20% to 65% in puppies with congenital nephrogenic diabetes insipidus ().
Selections from the book: “Veterinary pediatrics: dogs and cats from birth to six months”. Johnny D. Hoskins. (2001)