Renal enlargement is usually detected by physical examination or by abdominal radiography or by ultrasonography. A quick rule of thumb is that the kidney lenght on abdominal radiographs should be approximately equivalent to 2.5 to 3.0 times the lenght of the second lumbar vertebra in cats and 2.5 to 3.5 times length of the second lumbar vertebra in dogs.
Enlarged kidneys with a normal shape can be caused by edema, acute inflammation, diffusely infiltrating neoplastic disease, unilateral compensatory hypertrophy, trauma (intracapsular hemorrhage), or hydronephrosis. Enlarged, abnormally shaped kidneys may be caused by renal neoplasia, cysts, abscesses, hydronephrosis, or hematomas.
Ultrasonography and intravenous urography can be used to further define kidney shape and reveal internal details. Ultrasonography is particularly useful for evaluating enlarged kidneys associated with fluid accumulation (e.g., hydronephrosis, abscesses, and perirenal and parenchymal cysts), and can also be used to guide fine-needle aspiration or needle biopsy of the affected kidney.
Kidney biopsy is often necessary to confirm the cause of the renomegaly; however, biopsy is contraindicated if only one kidney is present or if a bleeding disorder, hydronephrosis, a cyst, or an abscess is suspected.
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