Sigmoid (S-shaped) cross-fused renal ectopia associated with calculus in a 3-year-old child: A case report and literature review.

Sigmoid (S-shaped) crossed-fused renal ectopia is a rare congenital anomaly, infrequently complicated by urolithiasis. We report a 3-year-old male child presenting with abdominal pain, diarrhea, and intermittent fever, previously diagnosed with a renal stone. Imaging revealed a 13-mm pelvic stone in the lower ectopic kidney with moderate hydronephrosis; laboratory tests were normal. The patient underwent open nephrolithotomy via a right modified Gibson incision, achieving complete stone removal through a small avascular parenchymal incision. Recovery was uneventful, and stone composition analysis showed mixed calcium oxalate and calcium phosphate stone. Careful imaging and individualized surgical planning are essential in complex renal anatomy.