RENOMEGALY IN DOGS AND CATS .1. DIFFERENTIAL DIAGNOSES

Detection of renomegaly is important because, when combined with other clinical information (such as signalment and history), it provides a narrow list of differential diagnoses. Clinicians who are familiar wit h the potential causes of renomegaly can often quickly arrive at a def initive diagnosis with the aid of radiographic, ultrasonographic, cyto logic, or histopathologic information. Renomegaly is caused by various pathophysiologic processes, such as infiltration of the renal parench yma by inflammatory or neoplastic cells, alteration of renal structure by developmental disorders or renal insult, and distortion of the col lecting system secondary to urinary tract obstruction. In this review, the causes are grouped into several categories for ease of discussion : renomegaly caused by diffuse renal parenchymal disorders, such as ac ute renal failure, amyloidosis, renal lymphoma, pyogranulomatous nephr itis secondary to feline infectious peritonitis, and renal hypertrophy ; renomegaly caused by focal or multifocal parenchymal disorders, such as polycystic kidney disease and primary or metastatic renal neoplasi a; renomegaly caused by subcapsular and perirenal disorders, such as p erinephric pseudocysts and subcapsular and perirenal hematomas and abs cesses; and renomegaly caused by collecting system disorders, such as hydronephrosis and acute bacterial pyelonephritis. Part II of this rev iew will focus on the diagnostic approach to patients with renomegaly.