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

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.

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.

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.

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