RENOMEGALY IN DOGS AND CATS .2. DIAGNOSTIC-APPROACH

Renomegaly is an important clinical finding in small animal patients, not only because it provides a fairly narrow list of differential diag noses but also because it is easily investigated using minimally invas ive imaging techniques and fine-needle aspiration. Kidney enlargement may result from various pathophysiologic processes, such as infiltrati on of the renal parenchyma by inflammatory or neoplastic cells, altera tion of renal structure by developmental disorders or renal insult, an d distortion of the collection system secondary to urinary tract obstr uction. For ease of discussion, causes of renomegaly can be grouped in to several categories - diffuse parenchymal disorders, such as acute r enal failure, amyloidosis, renal lymphoma, pyogranulomatous nephritis secondary to FIP, and renal hypertrophy; focal or multifocal parenchym al disorders, such as polycystic kidney disease and primary or metasta tic renal neoplasia; subcapsular and perirenal disorders, such as peri nephritic pseudocysts and subcapsular hematomas; and collecting system disorders, such as hydronephrosis and bacterial pyelonephritis. The d iagnostic approach to renomegaly is straightforward. When enlargement of one or both kidneys is identified during physical or radiographic e xamination, a list of differential diagnosis is formulated based on si gnalment, clinical signs, laboratory abnormalities, and survey radiogr aphic findings. This is followed by specific evaluation of the kidneys using contrast radiography or ultrasonography, which provides a more complete assessment of the renal parenchyma and collecting system. In some patients, ultrasonography or contrast radiography may provide a d efinitive diagnosis. In others, fine-needle aspiration or needle core biopsy of the kidney is required to obtain a definitive diagnosis.