The “Footprint” Sign in Voiding Cystourethrography Indicates Poor Renal Function in Vesicoureteral Reflux: Is It a Pop-Off Mechanism?

Background/Objectives: To assess the “footprint” sign in voiding cystourethrogram (VCUG) for its diagnostic and prognostic significance in indicating a “pop-off” mechanism that may reduce pressure on the contralateral kidney. Methods: A retrospective analysis included patients with a “footprint” sign or high-grade vesicoureteral reflux (VUR) in VCUG. They were categorized into two groups: those with (Group A) and those without (Group B) the “footprint” sign. Results: Among 55 patients (median age 18 months), 18 exhibited the “footprint” sign. Group A had predominantly male patients. Bilateral VUR was less common in Group A (38.9%) compared to Group B (51.4%), though not statistically significant (p-value: 0.385). The “footprint” sign was predominantly associated with the left side (77.8% in Group A). The median differential renal function (DRF) was significantly lower in kidneys with the “footprint” sign (11.5%) compared to those without (44.5%, p-value < 0.001). All patients with a DRF under 20% exhibited the “footprint” sign. Conclusions: The “footprint” sign correlates with poor renal function, suggesting a potential pop-off mechanism protecting the contralateral kidney. Management should prioritize the contralateral kidney with normal function. The “footprint” sign alone in VCUG may suffice to indicate compromised renal function, negating the need for further ipsilateral kidney assessment.