Metabolic and surgical predictors in horseshoe and pelvic ectopic kidneys

Horseshoe kidney (HSK) and pelvic ectopic kidney (PEK) are congenital anomalies linked to impaired urinary drainage and a higher risk of nephrolithiasis. Evidence regarding metabolic profiles and surgical outcomes in these groups remains sparse. This study assessed predictors of postoperative stone clearance and 12-month recurrence in patients with HSK and PEK undergoing endourological procedures intervention.

We conducted a retrospective analysis of 50 consecutive patients with CT-confirmed HSK or PEK treated with retrograde intrarenal surgery (RIRS) or mini-percutaneous nephrolithotomy (mini-PNL) over 12 months. All patients had a standardized 24-hour metabolic evaluation and imaging followup at 1, 6, and 12 months. Outcomes included stone-free status at one month and recurrence at one year. Predictors were assessed using univariable and multivariable logistic regression.

Stone-free status at 1 month was achieved in 62% of patients, with 22% having residual fragments ≥4 mm. Residual burden was strongly associated with recurrence, which occurred in 44% of the cohort. Patients with fragments ≥4 mm had the highest recurrence rate (72.7%), compared with 35.5% among stone-free individuals (p=0.047). Age was independently associated with reduced likelihood of achieving stone-free status (B = -0.069, p=0.011). Higher 24-hour urinary volume was the only biochemical parameter protective against recurrence (OR 0.243, p=0.039). Neither malformation type nor surgical technique significantly influenced postoperative outcomes or recurrence. Metabolic abnormalities were frequent but not predictive of stone type or recurrence.

In HSK and PEK, postoperative residual fragments and low urine volume are the main determinants of recurrence, whereas anatomical subtype and surgical approach have limited prognostic value. Strategies focused on complete stone clearance and hydration optimization may improve long-term outcomes in this patient population.