Electron beam computerized tomography assessment of in vivo single kidney glomerular filtration rate and tubular dynamics during chronic partial unilateral ureteral obstruction in the pig

Purpose: The assessment of hydronephrosis due to chronic partial ureteral o bstruction is controversial. We determined whether a new radiographic techn ique for assessing kidney function, electron beam computerized tomography ( CT), can detect altered renal physiology due to chronic partial ureteral ob struction. We also compared and contrasted electron beam CT with standard w ell tempered diuretic mercaptoacetyltriglycine (MAG-3) urography. Materials ands Methods: Six pigs underwent creation of unilateral partial u reteral occlusion or sham operation. Three weeks after surgery diuretic enh anced MAG-3 renal scan was done and 48 hours later contrast enhanced electr on beam CT was performed. Results: Mean differential function plus or minus standard error of mean of the obstructed kidney was 5.6% +/- 2.4% on MAG-3 renography. In contrast, electron beam CT revealed significantly preserved mean renal function at 24 .5% +/- 2.7% (p < 0.01). Electron beam CT analysis of tubular function reve aled persistent glomerular filtration and filtrate flow through the proxima l tubules and loop of Henle with a selective decrease in distal tubular flo w, which were findings suggestive of proximal tubular sparing that were not demonstrated by nuclear renography. Conclusions: Renal function on MAG-3 renography is primarily determined by measuring kidney perfusion and tubular secretion of the isotope. In contras t, electron beam CT determines renal function via quantifying the in vivo s ingle kidney glomerular filtration rate and by assessing renal tubular func tion. This study documents that electron beam CT of differential renal func tion is significantly different from that of MAG-3 renography. To our knowl edge which of these 2 radiographic studies is most clinically applicable is unknown to date.