Intrarenal backflow during retrograde pyelography with graded intrapelvic pressure. A radiologic study.

Intrarenal backflow (IRB)--a form of pyelorenal backflow where contrast material appears in the renal parenchyma during retrograde pyelography--seems to be the same phenomenon as intrarenal reflux (IRR), sometimes observed during micturating cystography in children or animals with vesicoureteral reflux. Retrograde pyelography experiments were performed on baby pigs to study the relationship between renal pelvic pressure and IRB. Intrapelvic pressure was raised to 30-35 mm Hg (moderate) or 70-75 mm Hg (high) for 5 minutes. IRB developed in only four of 12 kidneys at moderate pressure but in all six kidneys at high pressure. Similar experiments were conducted on kidneys which had been rendered temporarily ischemic prior to retrograde pyelography. Twenty-seven kidneys were so studied 30 minutes after a 30- or 60-minute period of ischemia. With moderate and high pressure retrograde pyelography, all kidneys developed IRB. The most intense and widespread IRB occurred after 60 minutes of ischemia and at high pressure. IRB localized to the upper pole most frequently but was also observed in other portions of the kidney. The effect of IRB upon renal blood flow (RBF) was determined with electromagnetic flow probes during the same experiments. IRB caused a 16% mean decrease in RBF at moderate pressures and a 57% mean decrease in RBF at high pressures and was independent of preceding ischemia. It is concluded that both raised intrapelvic pressure and preceding renal ischemia are important factors determining the degree of IRB during retrograde pyelography and that backflow itself causes decreased RBF.