Subtle obstructive uropathy resulting from encasement of the ureters by tumor

The diagnosis of obstructive uropathy may be difficult in the occasional case in which there is little or no dilatation of the collecting system. A case is presented in which anuric renal failure resulted from encasement of the ureters by tumor. The excretory urogram revealed a delayed pyelogram and a dense nephrogram with minimal dilatation of the collecting systems. The combination of a dense nephrogram and delayed pyelogram should raise the possibility of obstruction, regardless of the appearance of the collecting systems.