title: Percent improvement in renal pelvis antero-posterior diameter (PI-APD): Prospective validation and further exploration of cut-off values that predict success after pediatric pyeloplasty supporting safe monitoring with ultrasound alone.
abstract: BACKGROUND
  Renograms are frequently obtained post-pyeloplasty in patients with residual hydronephrosis to confirm adequate drainage. Recent evidence suggests that percent improvement in antero-posterior diameter (PI-APD) ≥38 is predictive of success. We sought to further explore PI-APD ranges that would allow identification of patients who would benefit from ultrasound (US) monitoring alone vs. post-operative renal scan, and those more likely to develop recurrent ureteropelvic junction obstruction (rUPJO).
  
  
  METHODS
  A single-center prospectively-collected pyeloplasty database (2008-2015) was queried (n = 151). Only patients with both pre- and post-operative APD measurements were included (n = 138). PI-APD was divided into 3 categories: <20%; 20-39%; ≥40%. The following variables were collected post-operatively: patients monitored with US alone, renogram and US, rUPJO and minimal or resolved hydronephrosis (SFU ≤2; UTD ≤1; APD ≤15 mm).
  
  
  RESULTS
  Mean age at first and last follow-up were 4.8 (median 4.0; range 0-60) months and 26.6 (median 20.5; range 1-77) months, respectively. Of 138 patients, 84 (61%) had US alone, 54 (39%) had a renogram and US post-operatively, and 6 (4%) developed rUPJO. Of 84 patients who had US alone, 71 (84%; p < 0.01) demonstrated ≥40% PI-APD. Of 54 patients with renogram and US 46 (85%; p < 0.01) had ≥40 PI-APD. Of the 6 patients who developed rUPJO, all were in the <20 PI-APD group (100%; p < 0.01). Resolution of hydronephrosis according to SFU, UTD and APD occurred in 96/138 (70%), 89/138 (64%) and 113/138 (82%) patients respectively. Of these, 87 (91%), 81 (91%), and 108 (95%) occurred in >40% PI-APD group.
  
  
  CONCLUSIONS
  ≥40% PI-APD at the first post-operative visit strongly predicts pyeloplasty success, as up to 82% of these patients showed resolved hydronephrosis and 61% underwent non-invasive monitoring by US alone. Our data suggests that up to 85% of renograms may have been unnecessary. Finally, <20% PI-APD permitted identification of all rUPJO cases. Stratification of patients based in PI-APD is a promising strategy for further minimizing radiation exposure while safely detecting children at risk for rUPJO.
authors.affiliation: McMaster Children's Hospital, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Rickard
authors.affiliation: McMaster Children's Hospital, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada; McMaster University, Division of Urology, Department of Surgery, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada; McMaster Pediatric Surgery Research Collaborative, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada. Electronic address: braga@mcmaster.ca.
authors.forename: L H
authors.initials: LH
authors.lastname: Braga
authors.affiliation: McMaster University, Division of Urology, Department of Surgery, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada.
authors.forename: J-P
authors.initials: JP
authors.lastname: Oliveria
authors.affiliation: Dalhousie University, 6299 South Street, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Romao
authors.affiliation: McMaster Children's Hospital, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada; McMaster University, Division of Urology, Department of Surgery, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Demaria
authors.affiliation: The Hospital for Sick Children, Division of Urology, 555 University Ave, Toronto, ON M5G 1X8, Canada.
authors.forename: A J
authors.initials: AJ
authors.lastname: Lorenzo
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D006869:Hydronephrosis / Q000209:etiology / Q000601:surgery; D007223:Infant; D007682:Kidney Pelvis / Q000033:anatomy & histology* / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008991:Monitoring, Physiologic; D009929:Organ Size; D011182:Postoperative Care; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011866:Radioisotope Renography; D016896:Treatment Outcome; D014463:Ultrasonography; D014517:Ureteral Obstruction / Q000150:complications / Q000000981:diagnostic imaging* / Q000601:surgery*; D013520:Urologic Surgical Procedures / Q000379:methods
keywords: Children; Post-operative; Pyeloplasty; Renal scan; Ureteropelvic junction obstruction