Assessment of post-pyeloplasty renal drainage in antenatally detected hydronephrosis by 99mTc-L, L-Ethylenedicysteine renal scintigraphy: the importance of delayed imaging.

Objective: Diuretic renal scintigraphy is important in diagnosing pelvi-ureteric junction obstruction (PUJO) in antenatally detected hydronephrotic (ANH) kidneys. Early-phase dynamic renal scintigraphy has several pitfalls contributing to the false interpretation of obstructed drainage, especially after pyeloplasty. This study explores the utility of delayed imaging in ^99mTc-L,L-Ethylenedicysteine (EC) diuretic renal scintigraphy to assess post-pyeloplasty renal drainage in ANH.

Methods: Data from May 2019 to January 2024 was retrospectively studied to identify infants with ANH who underwent surgery for PUJO and pre-and post-surgical assessment of renal drainage using ^99mTc-L,L-EC diuretic renal scintigraphy. Dynamic and post-void static images were analyzed to calculate percentage drainage till 3 h. Pre- and post-operative quantitative parameters were compared. Receiver operator curve analysis was done to calculate the threshold drainage to detect renal obstruction on postvoid images.

Results: In a cohort of 104 patients with a mean age of 10.1 ± 6.5 months (range 2-36 months) at surgery, 106 renal units (bilateral involvement in two patients) were analyzed. There was no significant difference in the sum of obstructive and equivocal curve patterns (105 vs 79, p = 0.06) and T_1/2 values (105 vs 82, p = 0.093) before and after surgery. However, there was a significant difference between the pre-and post-surgery median 3-h percentage drainage (26 vs 80%, p < 0.001). A drainage threshold of less than 59% at 3 h had 93.4% sensitivity and 92.5% specificity to detect obstructive drainage.

Conclusion: Delayed images in diuretic renal scintigraphy are crucial in accurately interpreting post-pyeloplasty drainage patterns and help overcome pitfalls of the dynamic study.