title: Pediatric ureteropelvic junction obstruction: can magnetic resonance urography identify crossing vessels?
abstract: BACKGROUND
  MR Urography (MRU) is an increasingly used imaging modality for the evaluation of pediatric genitourinary obstruction.
  
  
  OBJECTIVE
  To determine whether pediatric MR urography (MRU) reliably detects crossing vessels in the setting of suspected ureteropelvic junction (UPJ) obstruction. The clinical significance of these vessels was also evaluated.
  
  
  METHODS
  We identified pediatric patients diagnosed with UPJ obstruction by MRU between May 2009 and June 2014. MRU studies were evaluated by two pediatric radiologists for the presence or absence of crossing vessels. Ancillary imaging findings such as laterality, parenchymal thinning/scarring, trapped fluid in the proximal ureter, and presence of renal parenchymal edema were also evaluated. Imaging findings were compared to surgical findings. We used the Mann-Whitney U test to compare continuous data and the Fisher exact test to compare proportions.
  
  
  RESULTS
  Twenty-four of 25 (96%) UPJ obstructions identified by MRU were surgically confirmed. MRU identified crossing vessels in 10 of these cases, with 9 cases confirmed intraoperatively (κ = 0.92 [95% CI: 0.75, 1.0]). Crossing vessels were determined to be the primary cause of UPJ obstruction in 7/9 children intraoperatively, while in two children the vessels were deemed incidental and noncontributory to the urinary tract obstruction. There was no significant difference in age or the proportions of ancillary findings when comparing children without and with obstructing vessels.
  
  
  CONCLUSIONS
  MRU allows detection of crossing vessels in pediatric UPJ obstruction. Although these vessels are the primary cause of obstruction in some children, they are incidental and non-contributory in others. Our study failed to convincingly identify any significant predictors (e.g., age or presence of renal parenchymal edema) that indicate when a crossing vessel is the primary cause of obstruction.
authors.affiliation: Department of Radiology, University of Michigan Health System, Section of Pediatric Radiology, Mott Children's Hospital, 1540 E. Hospital Drive, Ann Arbor, MI, 48109, USA. pkushal@med.umich.edu.
authors.forename: Kushal R
authors.identifier: http://orcid.org/0000-0002-7394-2715
authors.initials: KR
authors.lastname: Parikh
authors.affiliation: Department of Radiology, University of Texas Southwestern, Dallas, TX, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Hammer
authors.affiliation: Department of Radiology, University of Michigan Health System, Section of Pediatric Radiology, Mott Children's Hospital, 1540 E. Hospital Drive, Ann Arbor, MI, 48109, USA.
authors.forename: Kate H
authors.initials: KH
authors.lastname: Kraft
authors.affiliation: Department of Radiology, University of Michigan Health System, Section of Pediatric Radiology, Mott Children's Hospital, 1540 E. Hospital Drive, Ann Arbor, MI, 48109, USA.
authors.forename: Vesna
authors.initials: V
authors.lastname: Ivančić
authors.affiliation: Department of Radiology, University of Michigan Health System, Section of Pediatric Radiology, Mott Children's Hospital, 1540 E. Hospital Drive, Ann Arbor, MI, 48109, USA.
authors.forename: Ethan A
authors.initials: EA
authors.lastname: Smith
authors.affiliation: Department of Radiology, University of Michigan Health System, Section of Pediatric Radiology, Mott Children's Hospital, 1540 E. Hospital Drive, Ann Arbor, MI, 48109, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Dillman
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003287:Contrast Media; D005260:Female; D005682:Gadolinium; D006571:Heterocyclic Compounds; D006801:Humans; D007089:Image Enhancement; D021621:Imaging, Three-Dimensional; D007223:Infant; D008279:Magnetic Resonance Imaging; D008297:Male; D009942:Organometallic Compounds; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014513:Ureter / Q000098:blood supply* / Q000473:pathology*; D014517:Ureteral Obstruction / Q000473:pathology*
chemical_list: D003287:Contrast Media; D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; C062402:gadoteridol; D005682:Gadolinium
keywords: Children; Crossing vessel; Magnetic resonance urography; Ureteropelvic junction obstruction