CT and ultrasonography of acute renal abnormalities.

Computed tomography and ultrasonography are important in the evaluation of patients with acute renal abnormalities, either as adjuncts or, less commonly, as alternatives to excretory urography. Ultrasonography has become the imaging procedure of choice in evaluation of acute renal failure. Detection of obstructive uropathy by ultrasonography is very accurate, although the potential pitfalls of minimal dilatation obstructive uropathy, false absence of caliectasis in dehydrated patients, and peripelvic cysts simulating hydronephrosis should be considered. Both CT and ultrasonography have improved our ability to define specific causes of intrinsic or extrinsic renal or ureteral obstructing lesions, including tumor, inflammatory masses, and calculi. Renal infections and infarctions also have characteristic appearances on CT and ultrasonography, though ultrasonography is somewhat limited by its inability to reliably demonstrate gas-containing or small abscesses, and its inability to provide functional information about the concentrating capacity of regional areas of the kidney.