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

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.

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.

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).

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.