THE CT NEPHROGRAM - IMPLICATIONS FOR EVALUATION OF URINARY-TRACT DISEASE

The urographic nephrogram is an important indicator of underlying func tional and structural renal disease. With expansions in use of cross-s ectional imaging, the computed tomographic (CT) nephrogram (ie, contra st material enhancement within the renal parenchyma) has assumed a gre ater role in the evaluation of urinary tract disorders. Both quantitat ive and qualitative nephrographic abnormalities are well demonstrated by CT, including global or segmental absence or persistence of the nep hrogram, slowed temporal progression, striated pattern, and rim patter n. Global absence is nearly always unilateral and is most often seen w ith blunt abdominal trauma with renal pedicle injury. Segmental absenc e is attributable to focal renal infarction, most Likely due to arteri al emboli. Global persistence, which is much more common than segmenta l persistence, may be unilateral (caused by renal artery stenosis, ren al vein thrombosis, or urinary tract obstruction) or bilateral (due to systemic hypotension, intratubular obstruction, or abnormalities in t ubular function). Striated nephrograms may be unilateral or bilateral and are caused by ureteric obstruction, acute pyelonephritis, contusio n, renal vein thrombosis, tubular obstruction, hypotension, and autoso mal recessive polycystic kidney disease. The rim pattern is most often associated with renal infarction and occasionally with acute tubular necrosis and renal vein thrombosis. Careful evaluation of the CT nephr ogram is an integral pan of the abdominal CT examination.