Stone Between Crossed Paths: Retrograde Intrarenal Surgery for Isthmic Calculus in the Setting of Renal and Gut Malformations

Horseshoe kidney is the most frequent type of renal fusion anomaly, and it often has associated changes in the orientation of the kidneys, anomalous vascular supply, and poor urinary drainage, as well as an increased risk of nephrolithiasis. Horseshoe kidney occurs in conjunction with intestinal malrotation very infrequently, and the anatomical and technical difficulties are significant because of the distorted anatomy of the kidney and the abnormal bowel position; therefore, careful preoperative planning and an individualized surgical strategy are needed for the management of renal calculi in these patients. A 63-year-old man with a six-month history of left loin pain, but no fever, dysuria, hematuria, or evidence of urinary tract infection, was found to have a horseshoe kidney with a 2.4 × 1.2 cm calculus in the renal isthmus on cross-sectional contrast-enhanced CT, as well as intestinal malrotation with abnormal bowel orientation and mesenteric vascular relationships. Given the complicated anatomy and risk of percutaneous access, the patient underwent retrograde intrarenal surgery with flexible ureteroscopy and holmium laser lithotripsy, with successful complete stone clearance and no intraoperative or postoperative complications. This case shows the value of performing an extensive anatomical evaluation before creating a plan tailored to a specific patient when treating patients with multiple congenital malformations. Additionally, this case shows that retrograde intrarenal surgery is a safe and effective way to minimally invasively treat complicated renal calculi inside the kidney when the anatomic space is difficult to access.