1. Pediatric Surgery Department, Fundación Jiménez Díaz University Hospital, Avenida de los Reyes Católicos, 2, 28040 Madrid, Spain
2. Institute for Health Research IdiPAZ, La Paz University Hospital, 28046 Madrid, Spain
3. Pediatric Surgery Department, Complejo Asistencial Universitario de León, 24071 Castilla y León, Spain
4. Pediatric Surgery Department, Navarra University Hospital, 31008 Pamplona, Spain
5. Pediatric Surgery Department, La Paz University Hospital, 28046 Madrid, Spain
6. Pediatric Surgery Department, Rey Juan Carlos University Hospital, 28933 Móstoles, Spain
7. Pediatric Surgery Department, Toledo University Hospital, 45005 Toledo, Spain
8. Pediatric Surgery Department, Villalba University Hospital, 28400 Villalba, Spain