Diuretic Renography in Hydronephrosis: Delayed Tissue Tracer Transit Accompanies Both Functional Decline and Tissue Reorganization

Abstract

The significance of delayed tissue tracer transit (TTT) of 99m Tcmercaptoacetyltriglycine ( 99m Tc-MAG3) has not been systematically evaluated in hydronephrosis. We sought to demonstrate that delayed TTT accompanies both functional decline and histomorphologic restructuring. Methods: Twenty 2-to 3-mo-old piglets with surgically induced partial unilateral ureteral stenosis were examined with magnetic resonance urography (MRU) to evaluate morphology and with 99m Tc-MAG3 diuretic renography (DR) to determine single-kidney function (SKF), evaluate the response to furosemide stimulation (RFS), and assess TTT. All animals had DR and MRU before and after surgery and a third DR after surgery. Piglets were sacrificed after the final DR for renal histology. A total histologic score (THS) was generated. Results: Preoperative DR demonstrated nonobstructive RFS, timely TTT, and balanced SKF in all 20 kidneys. After ureteral ligature, MRU demonstrated pelvic dilatation in all piglets. The postoperative DRs revealed 12 kidneys with delayed TTT in one or both followups. In these 12 kidneys, the SKF declined from 51% 6 4% to 18% 6 14%, and the THS was 9.0 6 4.0. Three kidneys always had timely TTT, balanced SKF, and a THS of 1.8 6 0.3. The contralateral, nonoperated kidneys had timely TTT and a THS of 1.2 6 0.9. Postoperative scintigrams showed that 3 of 8 kidneys (38%) with an obstructive RFS had timely TTT, which demonstrates that TTT and RFS are not equivalent. Conclusion: In hydronephrosis, a delayed TTT of 99m Tc-MAG3 accompanies both functional decline and histomorphologic restructuring in obstruction. According to the literature, a delayed TTT is determined by the filtration fraction of the kidneys and appears to identify an obstruction-mediated upregulated renin-angiotensin system.

Surgical and Non-surgical Follow-up Results of Ureteropelvic Junction Obstruction

“…Britton et al have suggested combined use of diuretic response and TTT parameters in the evaluation of obstruction [13]. Additionally Schlottmann and Murer et al have documented their findings with histologic changes in obstruction [4,14].…”

“…There are also more recent evaluation methods as an adjunct of renography which are tissue transit time (TTT). The delay in TTT is a result of compromised filtration fraction (FF) and reduction of glomerular filtration rate (GFR) [4]. Schlottman et al have indicated that a prolonged TTT requires surgical correction in patients with obstruction whose results have shown that significant functional decline can be predicted by delayed TTT in patients with obstruction [4].…”

“…The delay in TTT is a result of compromised filtration fraction (FF) and reduction of glomerular filtration rate (GFR) [4]. Schlottman et al have indicated that a prolonged TTT requires surgical correction in patients with obstruction whose results have shown that significant functional decline can be predicted by delayed TTT in patients with obstruction [4]. Britton et al have suggested combined use of diuretic response and TTT parameters in the evaluation of obstruction [13].…”

“…Another study indicated that despite successful surgery the diuretic response may not necessarily improve [2]. There is a new parameter called 'tissue tracer transit' which is a more discriminative parameter instead of diuretic response or differential renal function estimation in determination of necessity of surgery [3,4].…”

The predictive value of the renogram

“…The lack of cases in this series is, according to the authors, explained by the fact that the surgeons are of the opinion that kidneys with prolonged cortical transit should be operated upon. The only objective data provided by Schlotmann et al [20] and supporting that view is an experimental study on total or subtotal obstruction which is unlikely to reflect the partial obstruction existing in PUJ stenosis [21].…”