Evaluating the Resolution of Hydronephrosis Following Pyeloplasty for Ureteropelvic Junction Obstruction in the Adult Population

Objective: Patients with ureteropelvic junction obstruction (UPJO) present with varying degrees of hydronephrosis preoperatively and many heal with persistent hydronephrosis postoperatively despite a successful pyeloplasty, the significance of which is poorly understood. The study aims to illustrate the natural history of pre- and post-pyeloplasty hydronephrosis and determine whether degree of hydronephrosis is predictive of pyeloplasty failure in the adult population. Methods: We retrospectively reviewed patients 18+ years old who underwent robotic pyeloplasty for UPJO with available imaging at our institution in 2014–2024. Hydronephrosis categories were obtained from radiology reports: none (Group 1), mild (2), moderate (3), and severe (4). Anteroposterior diameter (APD) of renal pelvis was measured in mid-transverse view. Failure was defined as radiographically confirmed UPJO recurrence requiring intervention. p < 0.05 was considered statistically significant. Results: One hundred and ten patients were included, with pyeloplasty at median age of 52 years and pain as presentation in 66%. Median follow-up was 22 months. 8 patients had a failed pyeloplasty at median 5 months. 34% of patients had persistent hydronephrosis (88% in failure group vs 29% in success). Median time to maximal APD decrease was 9 months (4 months for preoperative Group 1, 9 months for Group 2, 16 months for Group 3, and 10 months for Group 4, p = 0.3). Conversion to Group 1 postoperatively was 92% for preoperative Group 2, 67% for Group 3, and 54% for Group 4. Postoperative, not preoperative, degree of hydronephrosis was associated with pyeloplasty failure ( p = 0.002 vs 0.564). Conclusion: Persistent hydronephrosis is common, affecting one-third of patients long-term despite successful pyeloplasty. Imaging surveillance of postoperative hydronephrosis remains valuable, as its severity is associated with pyeloplasty failure, with most failures becoming evident within 5 months. Patients should be counseled on the expected timeline of hydronephrosis resolution to avoid unnecessary anxiety and workups.