Radiology, Vol 151, 319-322, Copyright © 1984 by Radiological Society of North America
Urinary obstruction: pitfalls in the use of delayed contrast material washout for diagnosis
JH Newhouse, ES Amis Jr and RC Pfister
Delayed washout of contrast material from the renal collecting system has
been described as a reliable sign of urinary tract obstruction. However,
this finding may appear in the absence of obstruction. Experiments were
performed with cylinders containing meglumine iothalamate, which were
perfused with water and imaged. The effects of (a) varying flow rate, (b)
different volumes of the cylinders, and (c) presence of obstruction on the
rate of contrast material washout were observed. In addition, postoperative
urography and ureteral perfusion studies in 6 patients who had had
ureteropelvic junction obstruction successfully treated by pyeloplasty were
reviewed. In the experiments, it was found that changes in flow rate and
volume of the reservoir affected contrast material washout; however, the
presence of obstruction did not cause a delay in washout. Three of the 6
patients had delayed washout of contrast material on postoperative
urographic studies, although ureteral perfusion studies had excluded
obstruction. Additional mechanisms that may affect the washout of contrast
material are discussed.
