1. Pediatric Surgery Department, Complejo Asistencial Universitario de León, León, Castilla y León, Spain
2. Pathology Department, Hospital Universitario de Navarra, Pamplona, Navarra, Spain
3. Pathology Department, Hospital General Río Carrión, Palencia, Navarra, Spain
4. Pediatric Surgery Department, Hospital Universitario de Navarra, Pamplona, Navarra, Spain