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Basics ⬇

Basics

Definition

One or both kidneys are abnormally large as detected by abdominal palpation or diagnostic imaging.

Pathophysiology

The kidneys may become abnormally large because of abnormal cellular infiltration (e.g., inflammation, infection, and neoplasia), urinary tract obstruction, acute tubular necrosis, or development of renal cysts or pseudocysts.

Systems Affected

  • Endocrine/Metabolic-metabolic acidosis due to decreased elimination of acid by kidneys and inability to reclaim bicarbonate
  • Gastrointestinal-inappetence, vomiting, diarrhea, or melena due to gastrointestinal irritation or ulceration in patients with uremia
  • Hemic/Lymphatic/Immune-anemia due to blood loss or decreased red blood cell survival in patients with uremia; increased susceptibility to infections due to immune dysfunction in patients with uremia, and impaired production of erythropoietin
  • Hepatobiliary-bilateral renomegaly may occur in patients with portosystemic shunts.
  • Nervous-depression and lethargy associated with effect of uremic toxins on central nervous system.
  • Renal/Urologic-one or both kidneys are abnormally large.
  • Respiratory-tachypnea or respiratory distress due to uremic pneumonitis or compensatory response for metabolic acidosis

Signalment

  • Cat and dog
  • Polycystic kidney disease, a cause of renomegaly, occurs in several breeds of dogs (bull terrier, cairn terrier, and West Highland white terrier) and cats (Persian, longhaired cats, others)
  • Mode of inheritance is autosomal dominant in Bull terriers and Persian cats and autosomal recessive in cairn terriers and West Highland white terriers.

Signs

Historical Findings

  • May be asymptomatic, especially if only one kidney is affected
  • Lethargy
  • Loss of appetite
  • Weight loss
  • Vomiting
  • Diarrhea
  • Polyuria and polydipsia
  • Discolored urine
  • Abdominal enlargement
  • Lameness (rarely) because of hypertrophic osteopathy associated with renal neoplasia

Physical Examination Findings

  • Abdominal mass
  • Abdominal pain
  • One or both kidneys palpably large
  • Abdominal enlargement
  • One kidney enlarged; one kidney abnormally small
  • Dehydration
  • Pale mucous membranes
  • Oral ulcers
  • Uremic halitosis

Causes & Risk Factors

Developmental/Acquired Disorders

  • Hydronephrosis-can cause unilateral or bilateral renomegaly in dogs and cats; develops secondary to ureteral obstruction (e.g., urolithiasis, ureteral strictures, and neoplasia at trigone of urinary bladder) and ectopic ureters.
  • Polycystic kidney disease-causes bilateral renomegaly in cats and often leads to chronic kidney disease; more common in Persians and domestic longhair cats.
  • Hematoma-occurs secondarily to trauma; infrequent cause of renomegaly.
  • Compensatory hypertrophy-causes unilateral renomegaly and occurs secondary to abnormality of the other kidney (e.g., renal hypoplasia, renal dysplasia, previous damage or nephrectomy).
  • Perinephric pseudocyst-causes apparent unilateral or bilateral enlargement. Kidney size may be normal, but the subcapsular fluid accumulation makes the kidney appear large on palpation and radiography.

Metabolic

  • Portosystemic shunt, acromegaly
  • Males have larger kidneys than females

Neoplastic

  • Lymphoma-most often occurs in cats and causes bilateral renomegaly; some patients have unilateral renomegaly.
  • Renal carcinoma-most common renal tumor of dogs; often causes unilateral renomegaly; very malignant and rapidly metastatic to distant sites such as lungs.
  • Nephroblastoma-also called Wilms' tumor; a congenital renal tumor that affects young dogs, although it may not be diagnosed until the patient is much older; biologic behavior varies; usually unilateral.
  • Sarcomas-usually cause unilateral renomegaly and behave malignantly.
  • Cystadenocarcinoma-bilateral renal tumor that occurs in German shepherd dogs; often associated with skin lesions (i.e., nodular dermatofibrosis).

Infectious/Inflammatory

  • Amyloidosis.
  • Leptospirosis (dogs).
  • Feline infectious peritonitis.
  • Feline leukemia virus infection predisposes cats to development of renal lymphoma.
  • Acute kidney injury.
  • Renal abscess-localized abscess within renal parenchyma usually causes unilateral renomegaly in dogs and cats.

Toxic

  • Ethylene glycol toxicosis-can cause bilateral renomegaly secondary to renal tubular swelling and renal infiltration by calcium oxalate crystals.
  • Other toxins that cause acute renal injury (e.g., grapes/raisins, lilies).

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Must distinguish from other abdominal masses.
  • Confirmation may require diagnostic imaging procedures or exploratory celiotomy.

CBC/Biochemistry/Urinalysis

  • Azotemia, hyperphosphatemia, and inappropriately low urine-concentrating capacity.
  • Leukocytosis-infectious, inflammatory, and neoplastic causes of renomegaly.
  • Nonregenerative anemia-chronic kidney disease or inflammatory disorders.
  • Hyperglobulinemia-infectious or inflammatory disorders (e.g., feline infectious peritonitis).
  • Hematuria and proteinuria-renal neoplasia.
  • Polycythemia and extreme leukocytosis rarely accompany some renal neoplasms.
  • Neoplastic cells rarely observed in urine of patients with renal neoplasia.

Other Laboratory Tests

  • Test cats for feline leukemia virus infection if renal lymphoma is suspected.
  • Perform serum protein electrophoresis to distinguish between polyclonal and monoclonal hyperglobulinemia.
  • Evaluate paired titers for Leptospira spp. 2–3 weeks apart in dogs with suspected leptospirosis.

Imaging

Radiographic Findings

  • Survey abdominal radiographs indicated to confirm renomegaly and identify potential causes of ureteral obstruction (e.g., radiopaque ureteroliths).
  • Enlarged kidneys on the ventrodorsal view are >3 or 3.5 times the length of the second lumbar vertebra in cats or dogs, respectively.
  • Excretory urography or CT to confirm presence of renomegaly, hydronephrosis, and space-occupying masses of the kidneys.
  • Antegrade pyelography may be needed to exclude ureteral obstruction in some cats.
  • Thoracic radiography indicated to detect metastases in patients with renal neoplasia.

Ultrasonographic Findings

  • Helps distinguish between causes of renomegaly including polycystic kidney disease, perinephric pseudocysts, hydronephrosis, neoplasia, abscess, and subcapsular hematoma.
  • Acute inflammation (e.g., leptospirosis, ethylene glycol toxicosis) may be associated with increased cortical echogenicity, perinephric effusion, or a medullary band of increased echogenicity.

Diagnostic Procedures

  • Cytologic examination of fine-needle aspirate can confirm presence of renal cyst, abscess, and/or neoplasia (lymphoma). Due to potential for “seeding” of neoplastic cells in the abdominal wall, fine-needle aspiration should be avoided if other renal tumors (e.g., renal carcinoma) are suspected.
  • If no definitive diagnosis is made by cytologic evaluation of renal aspirates, renal biopsy may be indicated.

Treatment ⬆ ⬇

Treatment

Medications ⬆ ⬇

Medications

Drug(s)

Vary with the cause

Contraindications/Possible Interactions

Avoid nephrotoxic drugs.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Perform physical examination and weigh patient to assess hydration status.
  • Other tests (CBC, serum chemistries, urinalysis, blood pressure measurements) are indicated depending on the underlying cause and presence of other conditions (e.g., anemia, azotemia, hypertension, proteinuria).

Possible Complications

  • Chronic kidney disease, depending on underlying cause of renomegaly.
  • Paraneoplastic syndromes associated with renal tumors that produce hormone-like substances.

Miscellaneous ⬆

Miscellaneous

Zoonotic Potential

Leptospirosis can be spread by contact with infected urine.

Suggested Reading

Cuypers MD, Grooters AM, Williams J, et al. Renomegaly in dogs and cats. Part I: Differential diagnosis. Compend Contin Educ Pract Vet 1997, 19:1019–1033.

Authors Cathy E. Langston and Allyson C. Berent

Consulting Editor Carl A. Osborne

Acknowledgment The authors and editors acknowledge the prior contribution of S. Dru Forrester.