In a previous paper I1 enumerated the various theories explaining the cause of renal back pressure in cases of hypertrophied prostate, median bar and urethral stricture. I also presented a theory of my own which was based on a large number of roentgen studies made on patients suffering from these different conditions.
My method of examination consisted in first obtaining a cystogram. This was done to determine whether or not reflux occurred. If reflux was absent on both sides, catheters were inserted into the two ureters and sodium iodide was injected. If reflux was present on one side only, a pyelogram was made of the opposite, intact side.
I found that in cases of long standing obstruction in which the patients showed clinical evidence of back pressure there was often no reflux. Pyelography in these instances, however, showed marked dilatation of both ureters and kidney pelves. Even in patients