Quantifying Severe Functional Asymmetry and Superior Pole Cortical Loss in Pediatric Hydronephrosis: A 99mTc-DMSA Scintigraphy and Hybrid SPECT/CT Observational Analytic Study

Abstract

Background: Pediatric hydronephrosis presents a clinical dilemma regarding conservative monitoring versus surgical intervention. Ultrasonography visualizes pelvicalyceal distension but cannot quantify functioning nephron mass.

Objective: To investigate the analytical utility of technetium-99m dimercaptosuccinic acid (99mTc-DMSA) planar scintigraphy and hybrid SPECT/CT in unmasking severe functional cortical loss in a child with moderate anatomical hydronephrosis.

Methods: An observational analytic investigation was conducted in a 5-year-old girl with right hydronephrosis, history of congenital hypospadias repaired via four surgeries, and recurrent urinary tract infections (UTIs). Diagnostic evaluation combined renal ultrasonography with 99mTc-DMSA cortical scintigraphy (70.3 MBq intravenous) and hybrid SPECT/CT acquired 3 hours post-injection. Split differential renal function (DRF) was calculated using background-subtracted geometric mean: GM = √(Count_POST × Count_ANT). Objective causality assessment utilized Bradford Hill criteria and WHO-UMC frameworks.

Results: Ultrasonography demonstrated Society for Fetal Urology (SFU) Grade II right hydronephrosis (pelvic diameter 11.8 mm) with preserved parenchymal thickness (8.2 mm). Conversely, 99mTc-DMSA scintigraphy exposed severe functional collapse. Geometric mean DRF was 20.03% (count index 284) in the right kidney versus 79.97% (count index 1,130) in the left kidney (asymmetry ratio 3.99:1). Hybrid SPECT/CT verified 74.6% volumetric parenchymal contraction (18.4 cm³ right vs. 72.6 cm³ left) with transmural cortical loss and faint tracer uptake localized to the right superior pole. Causal modeling linked iterative pyelonephritis and high-pressure reflux to irreversible polar scarring, averting observational delay.

Conclusion: Technetium-99m DMSA scintigraphy with SPECT/CT resolves critical anatomical-functional discordance, revealing end-stage cortical compromise concealed by moderate ultrasonographic dilatation to guide nephron-sparing triage in pediatric uropathy.